• Aonashi, K., and Coauthors, 2009: GSMaP passive, microwave precipitation retrieval algorithm: Algorithm description and validation. J. Meteor. Soc. Japan, 87A, 119136.

    • Search Google Scholar
    • Export Citation
  • Bao, J., S. Michelson, P. Neiman, F. Ralph, and J. Wilczak, 2006: Interpretation of enhanced integrated water vapor bands associated with extratropical cyclones: Their formation and connection to tropical moisture. Mon. Wea. Rev., 134, 10631080, doi:10.1175/MWR3123.1.

    • Search Google Scholar
    • Export Citation
  • Charney, J., 1955: The use of the primitive equations of motion in numerical prediction. Tellus, 7A, 2226, doi:10.1111/j.2153-3490.1955.tb01138.x.

    • Search Google Scholar
    • Export Citation
  • Dacre, H. F., P. A. Clark, O. Martinez-Alvarado, M. A. Stringer, and D. A. Lavers, 2015: How do atmospheric rivers form? Bull. Amer. Meteor. Soc., 96, 12431255, doi:10.1175/BAMS-D-14-00031.1.

    • Search Google Scholar
    • Export Citation
  • Davis, C. A., and K. A. Emanuel, 1991: Potential vorticity diagnostics of cyclogenesis. Mon. Wea. Rev., 119, 19291953, doi:10.1175/1520-0493(1991)119<1929:PVDOC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Dettinger, M. D., F. M. Ralph, T. Das, P. J. Neiman, and D. R. Cayan, 2011: Atmospheric rivers, floods and the water resources of California. Water, 3, 445478, doi:10.3390/w3020445.

    • Search Google Scholar
    • Export Citation
  • Gimeno, L., R. M. Trigo, P. Ribera, and J. A. Garcia, 2007: Editorial: Special issue on cut-off low systems (COL). Meteor. Atmos. Phys., 96, 12, doi:10.1007/s00703-006-0216-5.

    • Search Google Scholar
    • Export Citation
  • Gimeno, L., R. Nieto, M. Vázquez, and D. A. Lavers, 2014: Atmospheric rivers: A mini-review. Front Earth Sci., 2, doi:10.3389/feart.2014.00002.

    • Search Google Scholar
    • Export Citation
  • Hamada, A., Y. N. Takayabu, C. Liu, and E. J. Zipser, 2015: Weak linkage between the heaviest rainfall and tallest storms. Nat. Commun., 6, 6213, doi:10.1038/ncomms7213.

    • Search Google Scholar
    • Export Citation
  • Hirota, N., Y. N. Takayabu, M. Watanabe, M. Kimoto, and M. Chikira, 2014: Role of convective entrainment in spatial distributions of and temporal variations in precipitation over tropical oceans. J. Climate, 27, 87078723, doi:10.1175/JCLI-D-13-00701.1.

    • Search Google Scholar
    • Export Citation
  • Horinouchi, T., 2014: Influence of upper tropospheric disturbances on the synoptic variability of precipitation and moisture transport over summertime East Asia and the northwestern Pacific. J. Meteor. Soc. Japan, 92, 519541, doi:10.2151/jmsj.2014-602.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., M. E. McIntyre, and A. W. Robertson, 1985: On the use and significance of isentropic potential vorticity maps. Quart. J. Roy. Meteor. Soc., 111, 877946, doi:10.1002/qj.49711147002.

    • Search Google Scholar
    • Export Citation
  • Hu, K., R. Lu, and D. Wang, 2010: Seasonal climatology of cut-off lows and associated precipitation patterns over northeast China. Meteor. Atmos. Phys., 106, 3748, doi:10.1007/s00703-009-0049-0.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., and J. E. Martin, 2005: Tropical plumes and extreme precipitation in subtropical and tropical West Africa. Quart. J. Roy. Meteor. Soc., 131, 23372365, doi:10.1256/qj.04.148.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., H. Wernli, and G. Gläser, 2013: A global climatology of tropical moisture exports. J. Climate, 26, 30313045, doi:10.1175/JCLI-D-12-00401.1.

    • Search Google Scholar
    • Export Citation
  • Kobayashi, S., and Coauthors, 2015: The JRA-55 Reanalysis: General specifications and basic characteristics. J. Meteor. Soc. Japan, 93, 548, doi:10.2151/jmsj.2015-001.

    • Search Google Scholar
    • Export Citation
  • Lavers, D. A., and G. Villarini, 2013: The nexus between atmospheric rivers and extreme precipitation across Europe. Geophys. Res. Lett., 40, 32593264, doi:10.1002/grl.50636.

    • Search Google Scholar
    • Export Citation
  • Lavers, D. A., R. P. Allan, E. F. Wood, G. Villarini, D. J. Brayshaw, and A. J. Wade, 2011: Winter floods in Britain are connected to atmospheric rivers. Geophys. Res. Lett., 38, L23803, doi:10.1029/2011GL049783.

    • Search Google Scholar
    • Export Citation
  • Molekwa, S., C. J. Engelbrecht, and C. J. deW Rautenbach, 2014: Attributes of cut-off low induced rainfall over the Eastern Cape province of South Africa. Theor. Appl. Climatol., 118, 307318, doi:10.1007/s00704-013-1061-3.

    • Search Google Scholar
    • Export Citation
  • Murakami, M., T. Clark, and W. Hall, 1994: Numerical simulations of convective snow clouds over the Sea of Japan; two-dimensional simulations of mixed layer development and convective snow cloud formation. J. Meteor. Soc. Japan, 72, 4362.

    • Search Google Scholar
    • Export Citation
  • Neiman, P. J., F. M. Ralph, G. A. Wick, J. D. Lundquist, and M. D. Dettinger, 2008: Meteorological characteristics and overland precipitation impacts of atmospheric rivers affecting the West Coast of North America based on eight years of SSM/I satellite observations. J. Hydrometeor., 9, 2247, doi:10.1175/2007JHM855.1.

    • Search Google Scholar
    • Export Citation
  • Neiman, P. J., L. J. Schick, F. M. Ralph, M. Hughes, and G. A. Wick, 2011: Flooding in western Washington: The connection to atmospheric rivers. J. Hydrometeor., 12, 13371358, doi:10.1175/2011JHM1358.1.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., and Coauthors, 2005: Climatological features of cutoff low systems in the Northern Hemisphere. J. Climate, 18, 30853103, doi:10.1175/JCLI3386.1.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., and Coauthors, 2007: Analysis of the precipitation and cloudiness associated with COLs occurrence in the Iberian Peninsula. Meteor. Atmos. Phys., 96, 103119, doi:10.1007/s00703-006-0223-6.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., M. Sprenger, H. Wernli, R. Trigo, and L. Gimeno, 2008: Identification and climatology of cut-off lows near the tropopause. Ann. N.Y. Acad. Sci., 1146, 256290, doi:10.1196/annals.1446.016.

    • Search Google Scholar
    • Export Citation
  • Ralph, F. M., P. J. Neiman, and G. A. Wick, 2004: Satellite and CALJET aircraft observations of atmospheric rivers over the eastern North Pacific Ocean during the winter of 1997/98. Mon. Wea. Rev., 132, 17211745, doi:10.1175/1520-0493(2004)132<1721:SACAOO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ralph, F. M., P. J. Neiman, G. A. Wick, S. I. Gutman, M. D. Dettinger, D. R. Cayan, and A. B. White, 2006: Flooding on California’s Russian River: Role of atmospheric rivers. Geophys. Res. Lett., 33, L13801, doi:10.1029/2006GL026689.

    • Search Google Scholar
    • Export Citation
  • Ralph, F. M., P. J. Neiman, G. N. Kiladis, K. Weickmann, and D. W. Reynolds, 2011: A multiscale observational case study of a Pacific atmospheric river exhibiting tropical–extratropical connections and a mesoscale frontal wave. Mon. Wea. Rev., 139, 11691189, doi:10.1175/2010MWR3596.1.

    • Search Google Scholar
    • Export Citation
  • Ramos, A. M., R. M. Trigo, M. L. R. Liberato, and R. Tomé, 2015: Daily precipitation extreme events in the Iberian Peninsula and its association with atmospheric rivers. J. Hydrometeor., 16, 579597, doi:10.1175/JHM-D-14-0103.1.

    • Search Google Scholar
    • Export Citation
  • Rutz, J. J., W. J. Steenburgh, and F. M. Ralph, 2014: Climatological characteristics of atmospheric rivers and their inland penetration over the western United States. Mon. Wea. Rev., 142, 905921, doi:10.1175/MWR-D-13-00168.1.

    • Search Google Scholar
    • Export Citation
  • Sakamoto, K., and M. Takahashi, 2005: Cut off and weakening processes of an upper cold low. J. Meteor. Soc. Japan, 83, 817834, doi:10.2151/jmsj.83.817.

    • Search Google Scholar
    • Export Citation
  • Sato, N., K. Sakamoto, and M. Takahashi, 2005: An air mass with high potential vorticity preceding the formation of the Marcus Convergence Zone. Geophys. Res. Lett., 32, L17801, doi:10.1029/2005GL023572.

    • Search Google Scholar
    • Export Citation
  • Takayabu, Y. N., J. Yokomori, and K. Yoneyama, 2006: A diagnostic study on interactions between atmospheric thermodynamic structure and cumulus convection over the tropical western Pacific Ocean and over the Indochina peninsula. J. Meteor. Soc. Japan, 84, 151169, doi:10.2151/jmsj.84A.151.

    • Search Google Scholar
    • Export Citation
  • Thorpe, A., 1985: Diagnosis of balanced vortex structure using potential vorticity. J. Atmos. Sci., 42, 397406, doi:10.1175/1520-0469(1985)042<0397:DOBVSU>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tsuboki, K., 2008: High-resolution simulations of high-impact weather systems using the cloud-resolving model on the earth simulator. High Resolution Numerical Modelling of the Atmosphere and Ocean, K. Hamilton and W. Ohfuchi, Eds., Springer, 141–156.

  • Tsuboki, K., and Y. Ogura, 1999: A potential vorticity analysis of thunderstorm-related cold lows. Tenki, 46, 453459.

  • Tsuboki, K., and A. Sakakibara, 2002: Large-scale parallel computing of cloud resolving storm simulator. High Performance Computing, H. P. Zima et al., Eds., Lecture Notes in Computer Science, Vol. 2327, Springer, 243–259.

  • Viale, M., and M. N. Nuñez, 2011: Climatology of winter orographic precipitation over the subtropical central Andes and associated synoptic and regional characteristics. J. Hydrometeor., 12, 481507, doi:10.1175/2010JHM1284.1.

    • Search Google Scholar
    • Export Citation
  • Waliser, D. E., and Coauthors, 2012: The “year” of tropical convection (May 2008–April 2010): Climate variability and weather highlights. Bull. Amer. Meteor. Soc., 93, 11891218, doi:10.1175/2011BAMS3095.1.

    • Search Google Scholar
    • Export Citation
  • Zhu, Y., and R. E. Newell, 1998: A proposed algorithm for moisture fluxes from atmospheric rivers. Mon. Wea. Rev., 126, 725735, doi:10.1175/1520-0493(1998)126<0725:APAFMF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • View in gallery

    (a) Time series of precipitation (mm h−1) from JMA gauge measurements in Hiroshima (red bars), from GSMaP on a 0.1° × 0.1° grid of Hiroshima (dashed black line), from GSMaP averaged over the 1.5° × 0.8° box indicated by the pink box in Hiroshima in (b) (solid black line), from the JMA forecast averaged over the 1.5° × 0.8° box (orange lines), and from the Ctl experiment averaged over the 1.5° × 0.8° box (blue line). The scale for the gauge measurement and the GSMaP 0.1° × 0.1° grid is shown on the right of the figure, and that for the GSMaP 1.5° × 0.8° box, the JMA forecast, and the Ctl experiment is shown on the left. (b) Horizontal distribution of precipitation (mm h−1) based on the GSMaP during 1300–2400 UTC 19 Aug 2014. (c) Precipitable water (shading; mm) and horizontal wind at 250 hPa (vectors; m s−1) during 1300–2400 UTC 19 Aug 2014. Contours in (c) show 250-hPa geopotential height of 10 970 m at 1800 UTC 17 Aug (light blue), 18 Aug (blue), and 19 Aug (dark blue). Large-scale atmospheric field variables in (c) were derived from JRA-55 data.

  • View in gallery

    (a),(b) Relative humidity (shading; %) and circulation (vectors; m s−1, hPa h−1) along a cross section from northwest to southeast [shown by the dashed red line in (c)–(f)]. (c)–(f) Humidity (shading; mm) and water vapor flux (vectors; mm m s−1) vertically integrated (c),(d) below 800 and (e),(f) above 800 hPa. The vertical integrations are calculated as and using the lowest seven pressure levels below 800 hPa and the higher nine pressure levels above 800 hPa. (a),(c),(e) The average during 1300–2400 UTC 19 Aug and (b),(d),(f) the climatological average. Hatching in (c),(e) indicates precipitation >1 mm h−1. Variables were obtained from the MSM analysis.

  • View in gallery

    (a) Potential vorticity anomalies at 250 hPa (PVU; 1 PVU = 10−6 K kg−1 m2 s−1) and (b) temperature anomalies along the northwest–southeast cross section, shown by the dashed red line. Inverted dynamical vertical velocity (c) at 600 hPa and (d) along the northwest–southeast cross section (hPa h−1). Hatching indicates unstable regions with stability anomalies <−0.3 × 10−6 m2 Pa−2 s−2 at 600 hPa and the cross section.

  • View in gallery

    (a),(b) Potential vorticity anomalies (PVU), and inverted dynamical vertical velocity (hPa h−1) at (c),(d) 600 hPa and (e),(f) along the northwest to southeast cross section associated with (a),(c),(e) the COL and (b),(d),(f) the trough. Contours in (a),(b) show the factor for extracting the PV associated with the COL and the trough. Hatching indicates unstable regions with stability anomalies <−0.3 × 10−6 m2 Pa−2 s−2 at 600 hPa and the cross section.

  • View in gallery

    Topography used in the model experiments (m).

  • View in gallery

    Results of the Ctl experiment. (a) Precipitation (shading; mm h−1) and surface height of 300 m (brown contours). (b) Relative humidity (shading; %) and circulation (vectors; m s−1, hPa h−1) along the northwest–southeast cross section. Humidity (shading; mm) and water vapor flux (vectors; mm m h−1) vertically integrated (c) below 800 and (d) above 800 hPa. Hatching in (c),(d) indicates the convergence of water vapor flux >1.5 mm h−1. (e) Geopotential height anomalies at 250 hPa.

  • View in gallery

    As in Fig. 6, but for the ClmQfree experiment.

  • View in gallery

    As in Fig. 6, but for the ClmQboundary experiment.

  • View in gallery

    As in Fig. 6, but for the NoCOL experiment.

  • View in gallery

    As in Fig. 6, but for the NoTrough experiment.

  • View in gallery

    As in Fig. 6, but for the NoMountain experiment.

  • View in gallery

    Schematic representation showing the relationship between the precipitation event in Hiroshima (pink cross) and the large-scale atmospheric field. The deep structure of the AR is shown in blue. The COL and its associated dynamical ascent are shown in brown. The trough and its dynamical ascent are shown in red. The color of the bottom map represents surface topography.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 289 273 21
PDF Downloads 266 247 25

Roles of an Atmospheric River and a Cutoff Low in the Extreme Precipitation Event in Hiroshima on 19 August 2014

View More View Less
  • 1 National Institute of Polar Research, and Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan
  • | 2 Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan
  • | 3 Hydrospheric Atmospheric Research Center, Nagoya University, Aichi, Japan
  • | 4 Geosphere Environmental Technology Corporation, Tokyo, Japan
© Get Permissions
Full access

Abstract

Precipitation in excess of 100 mm h−1 in Hiroshima, Japan, on 19 August 2014, caused a flash flood that resulted in 75 deaths and destroyed 330 houses. This study examined the meteorological background of this fatal flood. During this event, considerable filamentary transport of water vapor from the Indochina Peninsula to the Japanese islands occurred, forming a so-called atmospheric river (AR). This AR had a deep structure with an amount of free tropospheric moisture comparable with that of the boundary layer. Furthermore, a cutoff low (COL), detached from the subtropical jet over the central Pacific, moved northwestward to the Japanese islands. Instability associated with the cold core of the COL and dynamical ascent induced in front of it, interacted with the free tropospheric moisture of the AR, which caused the considerable precipitation in Hiroshima. Moreover, the mountains of the Japanese islands played a role in localizing the precipitation in Hiroshima. These roles were separately evaluated on the basis of sensitivity experiments with a cloud-resolving model.

Denotes Open Access content.

Corresponding author address: Nagio Hirota, National Institute of Polar Research, 10-3, Midoricho, Tachikawa, Tokyo 190-8518, Japan. E-mail: nagio@aori.u-tokyo.ac.jp

Abstract

Precipitation in excess of 100 mm h−1 in Hiroshima, Japan, on 19 August 2014, caused a flash flood that resulted in 75 deaths and destroyed 330 houses. This study examined the meteorological background of this fatal flood. During this event, considerable filamentary transport of water vapor from the Indochina Peninsula to the Japanese islands occurred, forming a so-called atmospheric river (AR). This AR had a deep structure with an amount of free tropospheric moisture comparable with that of the boundary layer. Furthermore, a cutoff low (COL), detached from the subtropical jet over the central Pacific, moved northwestward to the Japanese islands. Instability associated with the cold core of the COL and dynamical ascent induced in front of it, interacted with the free tropospheric moisture of the AR, which caused the considerable precipitation in Hiroshima. Moreover, the mountains of the Japanese islands played a role in localizing the precipitation in Hiroshima. These roles were separately evaluated on the basis of sensitivity experiments with a cloud-resolving model.

Denotes Open Access content.

Corresponding author address: Nagio Hirota, National Institute of Polar Research, 10-3, Midoricho, Tachikawa, Tokyo 190-8518, Japan. E-mail: nagio@aori.u-tokyo.ac.jp

1. Introduction

Extreme precipitation of over 100 mm h−1 occurred in Hiroshima, Japan, at around 1800 UTC 19 August 2014. Overall, 75 lives were lost and 330 houses destroyed in the associated landslides, which constituted the worst landslide disaster of the previous 30 years in Japan. As described in section 3, two large-scale atmospheric features played crucial roles in this event: an atmospheric river (AR) and a cutoff low (COL).

Atmospheric rivers are large transient filamentary regions of water vapor that cross the midlatitudes (Zhu and Newell 1998; Ralph et al. 2004; Gimeno et al. 2014). They are typically 300–500 km wide and can extend over several thousand kilometers in length, often occurring within the warm conveyor belt of extratropical cyclones. The moisture associated with ARs can be observed in the boundary layer as well as in the free troposphere (Ralph et al. 2004; Neiman et al. 2008). This deep structure results from local convergence along the cold front of extratropical cyclones and to some extent horizontal transport from the lower latitudes (Bao et al. 2006; Dacre et al. 2015). Several recent studies have highlighted the importance of free tropospheric moisture regarding the rainfall amount of well-organized precipitation systems (e.g., Takayabu et al. 2006; Hirota et al. 2014; Hamada et al. 2015).

Atmospheric rivers can be identified in the midlatitudes over the western and eastern Pacific, Atlantic, and southern Indian Ocean (Waliser et al. 2012; Knippertz et al. 2013). Although their structure is relatively narrow, covering only approximately 10% of Earth’s circumference, they account for over 90% of the total meridional water vapor transport across the midlatitudes at 35°N (Zhu and Newell 1998), suggesting their crucial role in the hydrological cycle. Atmospheric rivers have attracted increasing attention because they are important water resources and are often responsible for severe precipitation and flooding events (e.g., Dettinger et al. 2011). For example, ARs are related with heavy precipitation and flooding events on the western United States (Ralph et al. 2006; Neiman et al. 2008, 2011; Rutz et al. 2014), over the British river basins (Lavers et al. 2011), across western Europe (Lavers and Villarini 2013), in the Iberian Peninsula (Ramos et al. 2015), and over the Andes (Viale and Nunez 2011). Because of their vapor-rich characteristics, ARs can cause extreme precipitation when they encounter orographic lifting and/or synoptic disturbances (Ralph et al. 2006; Neiman et al. 2008, 2011; Lavers et al. 2011; Viale and Nunez 2011; Ralph et al. 2011; Lavers and Villarini 2013; Rutz et al. 2014; Ramos et al. 2015). It is also known that ARs are affected by large-scale atmospheric circulations such as North Atlantic Oscillation (Lavers and Villarini 2013).

COLs are isolated cyclonic vortices in the upper troposphere centered on 300 hPa that are detached from the basic westerly jet streams (Gimeno et al. 2007). They usually move erratically for several days before decaying because of diabatic heating associated with clouds and precipitation (Nieto et al. 2005, 2008). Their structure is characterized by positive potential vorticity (PV) near the tropopause and an underlying cold core within the troposphere (e.g., Sakamoto and Takahashi 2005). Associated with the PV, cyclonic circulation at the upper troposphere penetrates down to the lower troposphere. As air parcels move on the isentropic surfaces, dynamical ascending motions are induced in front of the low pressure systems (Thorpe 1985; Hoskins et al. 1985). COLs are reported as one of the most important factors causing extreme precipitation events when sufficient moisture is available within the lower to midtroposphere in the Iberian Peninsula (Nieto et al. 2007), West Africa (Knippertz and Martin 2005), East Asia (Hu et al. 2010), and South Africa (Molekwa et al. 2014). The dynamical ascent and atmospheric instabilities associated with the cold core trigger and/or enhance precipitation events (Tsuboki and Ogura 1999; Sato et al. 2005; Horinouchi 2014). It has also been shown that the northern-central Pacific is one of the regions most preferred for COL occurrence in summer (Nieto et al. 2008).

This study examined the roles of an AR and a COL in the extreme precipitation event in Hiroshima on 19 August 2014. We performed numerical experiments using a cloud-resolving model to evaluate the quantitative impacts of these factors separately. Special attention was given to the vertical distribution of moisture, which has an influence on the extreme rainfall amount. The model and the data used in this study are described in section 2, the results are provided in section 3, and a discussion and conclusions are stated in section 4.

2. Data and model

We used an hourly precipitation dataset of global satellite mapping of precipitation (GSMaP; Aonashi et al. 2009), version 6. The horizontal resolution of this dataset is 0.1° × 0.1° in latitude and longitude. We also used hourly precipitation data from gauge measurements in Hiroshima (34.55°N, 132.53°E) from the Japan Meteorological Agency (JMA). Atmospheric variables such as horizontal wind velocity, temperature, specific humidity, and surface pressure were obtained from the objective analysis of the mesoscale model (MSM) and the Japanese 55-year Reanalysis Project (JRA-55; Kobayashi et al. 2015); both datasets were produced by JMA. The MSM analysis dataset is based on the JMA forecasting model and used in their weather forecasts. The MSM analysis comprises a 3-hourly dataset with horizontal resolution of 0.125° × 0.1°, which is available just over East Asia (22.4°–47.6°N, 120°–150°E) from 2006, whereas the JRA-55 is a 6-hourly 1.25° × 1.25° gridded dataset over the entire globe from 1958. Merged satellite and in situ global daily sea surface temperature (MGDSST) data, compiled by the JMA, were also used.

In this study, the climatological average was defined as the 2006–14 average of a 30-day running mean calculated for each calendar day, and the anomaly was considered as the deviation from this climatological average. The 2006–14 period may be too short for defining climatology, but the regional analysis of MSM is available only from 2006. Using JRA-55, which is available from 1958, we have confirmed that the differences between the 2006–14 average and the 1958–2014 average are very small compared to the anomalies associated with the event (not shown). Therefore, we consider that the 2006–14 average can be used as “the climatology” in this context without affecting our main conclusions.

Numerical experiments were performed using a nonhydrostatic, compressible equation model called the Cloud-Resolving Storm Simulator (CReSS; Tsuboki and Sakakibara 2002; Tsuboki 2008). The horizontal resolution of this model is 2.5 km, and it has 36 vertical levels. The cloud physical processes are formulated using a bulk method of cold rain considering water vapor, rain, cloud, ice, snow, and graupel (Murakami et al. 1994). The parameterization of the subgrid-scale eddy motions is based on the 1.5-order closure with turbulent kinetic energy.

3. Results

a. Data analyses

First, we describe an overview of the precipitation event and the associated large-scale atmospheric field (Fig. 1). The time series of the precipitation gauge measurement (red bars in Fig. 1a) indicates that the observation site in Hiroshima (34.55°N, 132.53°E) recorded torrential rain with a maximum intensity of >100 mm h−1 at around 1800 UTC 19 August (0300 JST 20 August). This event was reflected in the GSMaP data as a maximum intensity of 70 mm h−1 at around 1700 UTC (dashed black line in Fig. 1a). The difference between the two datasets is a result of their different spatial representations.

Fig. 1.
Fig. 1.

(a) Time series of precipitation (mm h−1) from JMA gauge measurements in Hiroshima (red bars), from GSMaP on a 0.1° × 0.1° grid of Hiroshima (dashed black line), from GSMaP averaged over the 1.5° × 0.8° box indicated by the pink box in Hiroshima in (b) (solid black line), from the JMA forecast averaged over the 1.5° × 0.8° box (orange lines), and from the Ctl experiment averaged over the 1.5° × 0.8° box (blue line). The scale for the gauge measurement and the GSMaP 0.1° × 0.1° grid is shown on the right of the figure, and that for the GSMaP 1.5° × 0.8° box, the JMA forecast, and the Ctl experiment is shown on the left. (b) Horizontal distribution of precipitation (mm h−1) based on the GSMaP during 1300–2400 UTC 19 Aug 2014. (c) Precipitable water (shading; mm) and horizontal wind at 250 hPa (vectors; m s−1) during 1300–2400 UTC 19 Aug 2014. Contours in (c) show 250-hPa geopotential height of 10 970 m at 1800 UTC 17 Aug (light blue), 18 Aug (blue), and 19 Aug (dark blue). Large-scale atmospheric field variables in (c) were derived from JRA-55 data.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

Because this analysis aims to discuss the effects of large-scale factors, the time series of precipitation over a larger domain (a 1.5° × 0.8° box, indicated in pink in Fig. 1b) in Hiroshima is also shown in Fig. 1a (solid black line). Precipitation on 19 August started at around 0600 UTC and reached a maximum intensity of 5.5 mm h−1 at 1700 UTC. The cumulative precipitation for the day in the 1.5° × 0.8° box was about 30 mm. The standard deviation, calculated as the root-mean square of daily precipitation deviations from the climatology using data from 15 to 24 August of 2006–14, was about 9 mm. Therefore, the precipitation amount of 30 mm was about three standard deviations away from the climatological daily precipitation. Note that the JMA regional forecasting system did not predict such heavy precipitation from this event. The orange lines in Fig. 1a show the predicted precipitation over the 1.5° × 0.8° box, initialized at 0900, 1200, 1800, and 2100 UTC 19 August. The predicted precipitation amounts are very small compared with the observations (the precipitation predicted by the global JRA-55 system was also small; not shown).

The spatial distribution of precipitation, averaged from 1300 to 2400 UTC 19 August, is shown in Fig. 1b (hereafter, all figures represent 1300–2400 UTC 19 August unless specified otherwise). In addition to the rainfall peak over Hiroshima, a rainband can be identified over the northern coast of Kyushu (34.5°N, 130°E), and a broader rainy zone extends from the southwest to the northeast between the Korean Peninsula and the Japanese islands.

The large-scale atmospheric field is shown in Fig. 1c. Contours of geopotential height at 250 hPa (Z250) indicate significant deepening of a trough over China toward the time of the rainfall event, and a COL detached from the subtropical jet over the central Pacific moving toward the Japanese islands. A strong southwesterly associated with the trough can be observed from the Indochina Peninsula to Japan, and filamentary humid regions of precipitable water [vertically integrated water vapor from the surface to the top of atmosphere ] greater than 50 mm can be seen forming an AR that lasted for several days.

Figure 2 shows the vertical structure of the AR in comparison with the climatological field. The boundary layer is climatologically humid in this season, while the free troposphere is dry, except for the region in which the AR is located. The vertical cross section from the northwest to the southeast (dashed pink line in Figs. 2c–f) indicates that the humid region associated with the AR extends above 300 hPa (Fig. 2a). To compare the moisture in the boundary layer and the free troposphere quantitatively, we integrated the moisture below 800 hPa [] and above 800 hPa [], as shown in Figs. 2c–f. This dataset has seven pressure levels below 800 hPa and nine pressure levels above 800 hPa. The integrated moisture along the AR is about 30 mm, both in the boundary layer and in the free troposphere. The climatological values of the integrated moisture between Korea and Japan are about 27 mm in the boundary layer and about 20 mm in the free troposphere. Therefore, the effect of the AR on the anomalous moisture amount is very clear in the free troposphere but less so in the boundary layer.

Fig. 2.
Fig. 2.

(a),(b) Relative humidity (shading; %) and circulation (vectors; m s−1, hPa h−1) along a cross section from northwest to southeast [shown by the dashed red line in (c)–(f)]. (c)–(f) Humidity (shading; mm) and water vapor flux (vectors; mm m s−1) vertically integrated (c),(d) below 800 and (e),(f) above 800 hPa. The vertical integrations are calculated as and using the lowest seven pressure levels below 800 hPa and the higher nine pressure levels above 800 hPa. (a),(c),(e) The average during 1300–2400 UTC 19 Aug and (b),(d),(f) the climatological average. Hatching in (c),(e) indicates precipitation >1 mm h−1. Variables were obtained from the MSM analysis.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

The horizontal water vapor flux in Figs. 2c and 2e shows considerable northeastward transport of moisture along the AR in both the free troposphere and the boundary layer, where a strong ascending motion (vectors in Fig. 2a) accompanied by heavy precipitation (hatching in Figs. 2c and 2e) can be identified. Therefore, the anomalous free-tropospheric moisture of the AR is likely to have resulted from both horizontal transport from the lower latitudes and vertical transport, as suggested by Bao et al. (2006). Note that the surface evaporation anomaly along the AR was very small (not shown), and it did not contribute to the precipitable water of the AR.

Next, to examine the large-scale effects of the COL, the piecewise PV inversion technique developed by Davis and Emanuel (1991) was performed. Ertel’s PV is defined as
e1
where θ is potential temperature, is relative vorticity on the isentropic surface, and all other notations are standard. Assuming the hydrostatic balance and that the irrotational wind is much smaller than the nondivergent wind, PV can be written as
e2
where is geopotential, is the streamfunction, and is the Exner function. Applying the assumptions of the small irrotational wind to the divergence equation, the Charney (1955)’s balance equation is derived as
e3
This determines the horizontal velocity that is balanced with the geopotential. Note that this relationship reduces to geostrophic balance if the latitude dependency of f and the nonlinear terms are neglected. These two nonlinear equations in (2) and (3) are linearized in the same manner as Davis and Emanuel (1991) using the climatological field for the basic state:
e4
e5
where is a climatological field variable, is an anomalous field variable, and . Solving the linearized equations for , the balanced dynamical fields for the specified PV anomalies are diagnosed. The dynamical vertical motions can also be diagnosed from the balanced omega equation.

To solve these equations numerically, the standard successive over-relaxation (SOR) method was used, as in Davis and Emanuel (1991). The calculations were performed over East Asia (22.9°–46.9°N, 120.5°–149.5°E) with a horizontal resolution of 0.5° × 0.5° in latitude and longitude. The PV anomalies were evaluated using the MSM dataset, smoothed onto the 0.5° × 0.5° grid. Without this smoothing, balanced solutions cannot be obtained in the SOR calculations, probably because the original MSM gridded data with 0.125° × 0.1° resolution resolve some smaller-scale disturbances that are not balanced. The horizontal and vertical derivatives were evaluated using the centered differences. We applied the free edge boundary conditions except for the eastern edge, where were set to zero. The solid edge boundary condition at the east is also necessary to obtain balanced solutions in our SOR calculations. The effects of the condition on the results were limited because the eastern edge is suitably far from the region of interest around Hiroshima.

The PV anomalies at 250 hPa associated with the event are shown in Fig. 3a. The PV anomalies of the COL to the southeast of Japan and the trough over China can be identified. The vertical cross section of the temperature field shows that the COL is accompanied by a cold core in the troposphere (shading in Fig. 3b). Dry atmospheric stability, calculated as −(R/Cpp)∂(CpT + gZ)/∂p, is significantly decreased below the cold core maximum (stability anomalies less than −0.3 × 10−6 m2 Pa−2 s−2 are hatched in Fig. 3). Figure 3c shows the dynamical vertical motions diagnosed using the inverted dynamical field. The negative omega over the East China Sea and the Korean Peninsula indicates the dynamical ascending motion induced by the PV anomalies. These features are consistent with the typical circulation and thermal structure associated with the PV anomaly near the tropopause (Thorpe 1985; Hoskins et al. 1985).

Fig. 3.
Fig. 3.

(a) Potential vorticity anomalies at 250 hPa (PVU; 1 PVU = 10−6 K kg−1 m2 s−1) and (b) temperature anomalies along the northwest–southeast cross section, shown by the dashed red line. Inverted dynamical vertical velocity (c) at 600 hPa and (d) along the northwest–southeast cross section (hPa h−1). Hatching indicates unstable regions with stability anomalies <−0.3 × 10−6 m2 Pa−2 s−2 at 600 hPa and the cross section.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

The effects of the PV anomalies of the COL and the trough were evaluated separately. Each PV was extracted by multiplying a factor shown by the contours in Figs. 4a and 4b at all vertical levels.

Fig. 4.
Fig. 4.

(a),(b) Potential vorticity anomalies (PVU), and inverted dynamical vertical velocity (hPa h−1) at (c),(d) 600 hPa and (e),(f) along the northwest to southeast cross section associated with (a),(c),(e) the COL and (b),(d),(f) the trough. Contours in (a),(b) show the factor for extracting the PV associated with the COL and the trough. Hatching indicates unstable regions with stability anomalies <−0.3 × 10−6 m2 Pa−2 s−2 at 600 hPa and the cross section.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

To calculate the factor, the longitude and latitude of the location of the COL’s maximum PV anomaly at 250 hPa was determined. The radial distance in degrees from the maximum is given by
e6
and the factor for the COL is calculated as
e7
The factor for the trough is calculated as
e8
e9
Although these formulations are simple and include some empirical parameters, the calculated factors reasonably separated the PV anomalies of the COL and of the trough, as shown in Figs. 4a and 4b.

The dynamical vertical motions induced by the separate PV anomalies are shown in Figs. 4c and 4d, together with the instability anomalies. The large ascending motions over the East China Sea and the Korean Peninsula are induced by both the COL and the trough. The effect of the COL shows a maximum between the Korean Peninsula and the Japanese islands, whereas that of the trough is concentrated more over the Korean Peninsula. The induced 600-hPa omega of the COL is −1.18 hPa h−1 in Hiroshima, which is larger than that of the trough (−0.27 hPa h−1).

In summary, the very deep structure of the AR supplied a considerable amount of moisture to Hiroshima, and the instability, in conjunction with the dynamical ascending motions associated with the COL, appears to have contributed to the precipitation event. The COL with the cold core steepens the lapse rate, which increases the risk of destabilization and enhanced convection. Consistently, the regions of instability and ascending motion, overlapped along the southern edge of the AR, induce the effect of the free tropospheric moisture anomaly to trigger the deep convection. The trough had less impact on the ascending motion in Hiroshima. These large-scale factors, as well as orographic effects, are examined further based on numerical experiments in section 3b.

b. Numerical experiments

From the above analyses, the coexistence of the free tropospheric moisture anomaly associated with the AR and large-scale ascending motion, as well as midtropospheric instability associated with the COL, is suggested to have played an important role in the occurrence of the extreme rainfall event in Hiroshima. As the PV inversion merely diagnoses the large-scale condition for convection, the occurrence of the precipitation event was examined based on numerical experiments.

A series of numerical experiments using a cloud-resolving model was performed (starting at 1200 UTC 18 August until 2400 UTC 19 August) over a 1207.5 km × 817.5 km (483 × 327 grids) domain around Hiroshima. The topography used in the simulations is shown in Fig. 5, which reveals that many 500-m-high mountains are located on the Japanese islands. The initial and boundary conditions were prescribed using the MSM and MGDSST datasets. The configurations of each experiment are summarized in Table 1.

Fig. 5.
Fig. 5.

Topography used in the model experiments (m).

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

Table 1.

Summary of the initial and boundary conditions of the numerical experiments. An entry of “real” indicates the realistic values from 1200 UTC 18 Aug to 2400 UTC 19 Aug 2014. Anomalies of dynamical variables (u, υ, T, Z) associated with the COL and the trough were evaluated using the PV inversion analysis.

Table 1.

The control simulation (Ctl) was performed with realistic initial and boundary conditions. The results averaged from 1300 to 2400 UTC 19 August are shown in Fig. 6. The precipitation maximum in Hiroshima is well reproduced, whereas the rainy zone over the East China Sea is overestimated around 32°N, 129°E compared with the GSMaP observation (Figs. 6a and 1b). The time series of the simulated precipitation in the 1.5° × 0.8° box near Hiroshima is shown by the solid blue line in Fig. 1a. The precipitation starts to increase at around 0600 UTC and it reaches a maximum of 7 mm h−1 at 2100 UTC. The timing of the maximum lags somewhat (by about 5 h) and the precipitation amount is overestimated compared with the observations (solid black line in Fig. 1a). The moisture field is shown in Figs. 6b–d, which indicates that the water vapor transport associated with the AR had a deep structure with similar amounts of water vapor in the free troposphere and in the boundary layer, as found in the observations (Figs. 2a,b and 6c,d). Moisture convergence is also large, both in the boundary layer and in the free troposphere (hatching in Figs. 6c and 6d). The horizontal distribution of precipitation, including the local maximum in Hiroshima, is closer to the convergence in the free troposphere than in the boundary layer, suggesting the importance of the free tropospheric moisture. The COL is located at the southeastern end of the domain, which is strongly influenced by the imposed boundary conditions (Fig. 6e). Although some discrepancies with the observations exist, especially regarding the details of the precipitation distribution and the timing of the precipitation maximum, the experiments are shown to be reasonable for discussing the effects of the large-scale factors. The discrepancies are most likely related to the model cloud physics, which will be examined in future work.

Fig. 6.
Fig. 6.

Results of the Ctl experiment. (a) Precipitation (shading; mm h−1) and surface height of 300 m (brown contours). (b) Relative humidity (shading; %) and circulation (vectors; m s−1, hPa h−1) along the northwest–southeast cross section. Humidity (shading; mm) and water vapor flux (vectors; mm m h−1) vertically integrated (c) below 800 and (d) above 800 hPa. Hatching in (c),(d) indicates the convergence of water vapor flux >1.5 mm h−1. (e) Geopotential height anomalies at 250 hPa.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

To investigate the effect of the AR moisture, with particular attention on its vertical structure, two sensitivity experiments were performed by modifying the moisture field at specific vertical levels in the initial and boundary conditions. The first sensitivity experiment substituted the moisture in the free troposphere above 800 hPa to climatological values, rather than using the realistic values of the event (ClmQfree), and the second experiment substituted the moisture in the boundary layer below 800 hPa to the climatological values (ClmQboundary); the results are shown in Figs. 7 and 8, respectively. The precipitation maximum in Hiroshima has disappeared in ClmQfree but remains in ClmQboundary. The free tropospheric moisture and the moisture convergence are significantly reduced in ClmQfree because the free troposphere is very dry in the climatological field. Conversely, the moisture amount in ClmQboundary has changed little, even in the substituted boundary layer, because the boundary layer is also humid in the climatological field.

Fig. 7.
Fig. 7.

As in Fig. 6, but for the ClmQfree experiment.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

Fig. 8.
Fig. 8.

As in Fig. 6, but for the ClmQboundary experiment.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

Furthermore, sensitivity experiments were performed to evaluate the dynamical effects of the COL and the trough. The anomalies of the dynamical values (temperature, horizontal wind, and geopotential height) associated with the PV anomalies of the COL (NoCOL; Fig. 4a) and the trough (NoTrough; Fig. 4b) were subtracted from the initial and boundary conditions of the Ctl. In the NoCOL experiment, the COL was removed, as shown in Fig. 9e, and the results illustrate that the precipitation maximum over Hiroshima has disappeared (Fig. 9a). However, in the NoTrough experiment, the precipitation near the Korean Peninsula is reduced and the precipitation maximum over Hiroshima is shifted southward (Fig. 10a). These results are consistent with the dynamical forcing evaluated by the PV inversion technique (Fig. 4). The southern part of AR near Hiroshima is related more to the COL, whereas the dynamical ascending motion of the trough is concentrated nearer the Korean Peninsula.

Fig. 9.
Fig. 9.

As in Fig. 6, but for the NoCOL experiment.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

Fig. 10.
Fig. 10.

As in Fig. 6, but for the NoTrough experiment.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

A final sensitivity experiment was performed in which the topography was removed (the land–sea distribution was retained). The results are very similar to that of the Ctl, except that the precipitation maximum in Hiroshima extends farther northeastward (Fig. 11c), indicating that orographic effects on the model precipitation are localized over Hiroshima.

Fig. 11.
Fig. 11.

As in Fig. 6, but for the NoMountain experiment.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

4. Discussion and conclusions

This study investigated the extreme precipitation event that occurred in Hiroshima on 19 August 2014. Figure 12 summarizes the results of the study schematically. It was shown that the AR extending from the Indochina Peninsula to the Japanese islands, and the COL moving northwestward to Hiroshima from the central Pacific, were two important large-scale factors that caused the precipitation event. The AR provided a considerable amount of moisture, not only in the boundary layer but also in the free troposphere. The amount of moisture in the free troposphere was comparable with that in the boundary layer. Compared with the climatological average field, the anomalous moisture was especially apparent in the free troposphere, in contrast to the boundary layer. The COL, accompanying the cold core, caused instability in the middle troposphere and induced dynamical ascent ahead of it. The regions of the instability and ascending motions overlapped on the southern edge of the AR. The instability and ascending motions effectively used the free tropospheric moisture to generate the heavy precipitation of the event. Furthermore, the mountains of the Japanese islands caused the precipitation to be localized around Hiroshima. The numerical experiments reproduced the large precipitation maximum over Hiroshima only when the realistic deep AR moisture, COL, and topography were present in the model. The trough over China induced dynamical ascending motions around the Korean Peninsula. This also had some effect on the locations of both the precipitation maximum in Hiroshima and the rainy zone between the Korean Peninsula and the Japanese islands.

Fig. 12.
Fig. 12.

Schematic representation showing the relationship between the precipitation event in Hiroshima (pink cross) and the large-scale atmospheric field. The deep structure of the AR is shown in blue. The COL and its associated dynamical ascent are shown in brown. The trough and its dynamical ascent are shown in red. The color of the bottom map represents surface topography.

Citation: Monthly Weather Review 144, 3; 10.1175/MWR-D-15-0299.1

It is interesting to note that in the ClmQfree experiment, in which the free tropospheric moisture was reduced, precipitation was largely reduced in the southern part of the AR but it remained in the northern part (Fig. 9a). This suggests that the precipitation in the southern part was more sensitive to the free tropospheric moisture than in the northern part. One possible reason for this is the instability of the middle troposphere associated with the COL (Fig. 3b). As the COL was located to the south of the AR, the instability, dynamical uplift, and free tropospheric moisture could interact more effectively in the southern part. Consistent with this hypothesis, boundary layer convergence contributed largely to the precipitation in the northern part (Figs. 6c and 7c), while the contribution of the free tropospheric moisture convergence was also large in the southern part (Figs. 6d and 8d). Note that the moisture convergence over Hiroshima was very small in the MSM dataset (not shown), which is consistent with the underestimation of the precipitation event by the JMA forecasting system (Fig. 1a).

As this was a case study, it is difficult to discuss why the amount of precipitation of the event was three standard deviations away from the climatological daily precipitation. Some additional analyses indicated that the magnitude of the PV anomaly associated with the COL was more than 3 standard deviations away from the climatological value of the PV at this point, whereas that of the free tropospheric moisture anomaly was about 1.5 standard deviations away from its climatological value. It is considered very rare for such a strong COL to approach so close to the Japanese islands and for the free tropospheric moisture to be so large. Further statistical analyses are planned to investigate the relationship of extreme precipitation events with COLs and ARs.

Acknowledgments

This study was supported by the Green Network of Excellence Program and KAKENHI (15H02132) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and by the Environment Research and Technology Development Fund (2-1503) of the Ministry of the Environment, Japan. We also acknowledge the “Data Integration and Analysis System” fund for National Key Technology from MEXT. The Grid Analysis and Display System was used to plot the figures.

REFERENCES

  • Aonashi, K., and Coauthors, 2009: GSMaP passive, microwave precipitation retrieval algorithm: Algorithm description and validation. J. Meteor. Soc. Japan, 87A, 119136.

    • Search Google Scholar
    • Export Citation
  • Bao, J., S. Michelson, P. Neiman, F. Ralph, and J. Wilczak, 2006: Interpretation of enhanced integrated water vapor bands associated with extratropical cyclones: Their formation and connection to tropical moisture. Mon. Wea. Rev., 134, 10631080, doi:10.1175/MWR3123.1.

    • Search Google Scholar
    • Export Citation
  • Charney, J., 1955: The use of the primitive equations of motion in numerical prediction. Tellus, 7A, 2226, doi:10.1111/j.2153-3490.1955.tb01138.x.

    • Search Google Scholar
    • Export Citation
  • Dacre, H. F., P. A. Clark, O. Martinez-Alvarado, M. A. Stringer, and D. A. Lavers, 2015: How do atmospheric rivers form? Bull. Amer. Meteor. Soc., 96, 12431255, doi:10.1175/BAMS-D-14-00031.1.

    • Search Google Scholar
    • Export Citation
  • Davis, C. A., and K. A. Emanuel, 1991: Potential vorticity diagnostics of cyclogenesis. Mon. Wea. Rev., 119, 19291953, doi:10.1175/1520-0493(1991)119<1929:PVDOC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Dettinger, M. D., F. M. Ralph, T. Das, P. J. Neiman, and D. R. Cayan, 2011: Atmospheric rivers, floods and the water resources of California. Water, 3, 445478, doi:10.3390/w3020445.

    • Search Google Scholar
    • Export Citation
  • Gimeno, L., R. M. Trigo, P. Ribera, and J. A. Garcia, 2007: Editorial: Special issue on cut-off low systems (COL). Meteor. Atmos. Phys., 96, 12, doi:10.1007/s00703-006-0216-5.

    • Search Google Scholar
    • Export Citation
  • Gimeno, L., R. Nieto, M. Vázquez, and D. A. Lavers, 2014: Atmospheric rivers: A mini-review. Front Earth Sci., 2, doi:10.3389/feart.2014.00002.

    • Search Google Scholar
    • Export Citation
  • Hamada, A., Y. N. Takayabu, C. Liu, and E. J. Zipser, 2015: Weak linkage between the heaviest rainfall and tallest storms. Nat. Commun., 6, 6213, doi:10.1038/ncomms7213.

    • Search Google Scholar
    • Export Citation
  • Hirota, N., Y. N. Takayabu, M. Watanabe, M. Kimoto, and M. Chikira, 2014: Role of convective entrainment in spatial distributions of and temporal variations in precipitation over tropical oceans. J. Climate, 27, 87078723, doi:10.1175/JCLI-D-13-00701.1.

    • Search Google Scholar
    • Export Citation
  • Horinouchi, T., 2014: Influence of upper tropospheric disturbances on the synoptic variability of precipitation and moisture transport over summertime East Asia and the northwestern Pacific. J. Meteor. Soc. Japan, 92, 519541, doi:10.2151/jmsj.2014-602.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., M. E. McIntyre, and A. W. Robertson, 1985: On the use and significance of isentropic potential vorticity maps. Quart. J. Roy. Meteor. Soc., 111, 877946, doi:10.1002/qj.49711147002.

    • Search Google Scholar
    • Export Citation
  • Hu, K., R. Lu, and D. Wang, 2010: Seasonal climatology of cut-off lows and associated precipitation patterns over northeast China. Meteor. Atmos. Phys., 106, 3748, doi:10.1007/s00703-009-0049-0.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., and J. E. Martin, 2005: Tropical plumes and extreme precipitation in subtropical and tropical West Africa. Quart. J. Roy. Meteor. Soc., 131, 23372365, doi:10.1256/qj.04.148.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., H. Wernli, and G. Gläser, 2013: A global climatology of tropical moisture exports. J. Climate, 26, 30313045, doi:10.1175/JCLI-D-12-00401.1.

    • Search Google Scholar
    • Export Citation
  • Kobayashi, S., and Coauthors, 2015: The JRA-55 Reanalysis: General specifications and basic characteristics. J. Meteor. Soc. Japan, 93, 548, doi:10.2151/jmsj.2015-001.

    • Search Google Scholar
    • Export Citation
  • Lavers, D. A., and G. Villarini, 2013: The nexus between atmospheric rivers and extreme precipitation across Europe. Geophys. Res. Lett., 40, 32593264, doi:10.1002/grl.50636.

    • Search Google Scholar
    • Export Citation
  • Lavers, D. A., R. P. Allan, E. F. Wood, G. Villarini, D. J. Brayshaw, and A. J. Wade, 2011: Winter floods in Britain are connected to atmospheric rivers. Geophys. Res. Lett., 38, L23803, doi:10.1029/2011GL049783.

    • Search Google Scholar
    • Export Citation
  • Molekwa, S., C. J. Engelbrecht, and C. J. deW Rautenbach, 2014: Attributes of cut-off low induced rainfall over the Eastern Cape province of South Africa. Theor. Appl. Climatol., 118, 307318, doi:10.1007/s00704-013-1061-3.

    • Search Google Scholar
    • Export Citation
  • Murakami, M., T. Clark, and W. Hall, 1994: Numerical simulations of convective snow clouds over the Sea of Japan; two-dimensional simulations of mixed layer development and convective snow cloud formation. J. Meteor. Soc. Japan, 72, 4362.

    • Search Google Scholar
    • Export Citation
  • Neiman, P. J., F. M. Ralph, G. A. Wick, J. D. Lundquist, and M. D. Dettinger, 2008: Meteorological characteristics and overland precipitation impacts of atmospheric rivers affecting the West Coast of North America based on eight years of SSM/I satellite observations. J. Hydrometeor., 9, 2247, doi:10.1175/2007JHM855.1.

    • Search Google Scholar
    • Export Citation
  • Neiman, P. J., L. J. Schick, F. M. Ralph, M. Hughes, and G. A. Wick, 2011: Flooding in western Washington: The connection to atmospheric rivers. J. Hydrometeor., 12, 13371358, doi:10.1175/2011JHM1358.1.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., and Coauthors, 2005: Climatological features of cutoff low systems in the Northern Hemisphere. J. Climate, 18, 30853103, doi:10.1175/JCLI3386.1.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., and Coauthors, 2007: Analysis of the precipitation and cloudiness associated with COLs occurrence in the Iberian Peninsula. Meteor. Atmos. Phys., 96, 103119, doi:10.1007/s00703-006-0223-6.

    • Search Google Scholar
    • Export Citation
  • Nieto, R., M. Sprenger, H. Wernli, R. Trigo, and L. Gimeno, 2008: Identification and climatology of cut-off lows near the tropopause. Ann. N.Y. Acad. Sci., 1146, 256290, doi:10.1196/annals.1446.016.

    • Search Google Scholar
    • Export Citation
  • Ralph, F. M., P. J. Neiman, and G. A. Wick, 2004: Satellite and CALJET aircraft observations of atmospheric rivers over the eastern North Pacific Ocean during the winter of 1997/98. Mon. Wea. Rev., 132, 17211745, doi:10.1175/1520-0493(2004)132<1721:SACAOO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ralph, F. M., P. J. Neiman, G. A. Wick, S. I. Gutman, M. D. Dettinger, D. R. Cayan, and A. B. White, 2006: Flooding on California’s Russian River: Role of atmospheric rivers. Geophys. Res. Lett., 33, L13801, doi:10.1029/2006GL026689.

    • Search Google Scholar
    • Export Citation
  • Ralph, F. M., P. J. Neiman, G. N. Kiladis, K. Weickmann, and D. W. Reynolds, 2011: A multiscale observational case study of a Pacific atmospheric river exhibiting tropical–extratropical connections and a mesoscale frontal wave. Mon. Wea. Rev., 139, 11691189, doi:10.1175/2010MWR3596.1.

    • Search Google Scholar
    • Export Citation
  • Ramos, A. M., R. M. Trigo, M. L. R. Liberato, and R. Tomé, 2015: Daily precipitation extreme events in the Iberian Peninsula and its association with atmospheric rivers. J. Hydrometeor., 16, 579597, doi:10.1175/JHM-D-14-0103.1.

    • Search Google Scholar
    • Export Citation
  • Rutz, J. J., W. J. Steenburgh, and F. M. Ralph, 2014: Climatological characteristics of atmospheric rivers and their inland penetration over the western United States. Mon. Wea. Rev., 142, 905921, doi:10.1175/MWR-D-13-00168.1.

    • Search Google Scholar
    • Export Citation
  • Sakamoto, K., and M. Takahashi, 2005: Cut off and weakening processes of an upper cold low. J. Meteor. Soc. Japan, 83, 817834, doi:10.2151/jmsj.83.817.

    • Search Google Scholar
    • Export Citation
  • Sato, N., K. Sakamoto, and M. Takahashi, 2005: An air mass with high potential vorticity preceding the formation of the Marcus Convergence Zone. Geophys. Res. Lett., 32, L17801, doi:10.1029/2005GL023572.

    • Search Google Scholar
    • Export Citation
  • Takayabu, Y. N., J. Yokomori, and K. Yoneyama, 2006: A diagnostic study on interactions between atmospheric thermodynamic structure and cumulus convection over the tropical western Pacific Ocean and over the Indochina peninsula. J. Meteor. Soc. Japan, 84, 151169, doi:10.2151/jmsj.84A.151.

    • Search Google Scholar
    • Export Citation
  • Thorpe, A., 1985: Diagnosis of balanced vortex structure using potential vorticity. J. Atmos. Sci., 42, 397406, doi:10.1175/1520-0469(1985)042<0397:DOBVSU>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tsuboki, K., 2008: High-resolution simulations of high-impact weather systems using the cloud-resolving model on the earth simulator. High Resolution Numerical Modelling of the Atmosphere and Ocean, K. Hamilton and W. Ohfuchi, Eds., Springer, 141–156.

  • Tsuboki, K., and Y. Ogura, 1999: A potential vorticity analysis of thunderstorm-related cold lows. Tenki, 46, 453459.

  • Tsuboki, K., and A. Sakakibara, 2002: Large-scale parallel computing of cloud resolving storm simulator. High Performance Computing, H. P. Zima et al., Eds., Lecture Notes in Computer Science, Vol. 2327, Springer, 243–259.

  • Viale, M., and M. N. Nuñez, 2011: Climatology of winter orographic precipitation over the subtropical central Andes and associated synoptic and regional characteristics. J. Hydrometeor., 12, 481507, doi:10.1175/2010JHM1284.1.

    • Search Google Scholar
    • Export Citation
  • Waliser, D. E., and Coauthors, 2012: The “year” of tropical convection (May 2008–April 2010): Climate variability and weather highlights. Bull. Amer. Meteor. Soc., 93, 11891218, doi:10.1175/2011BAMS3095.1.

    • Search Google Scholar
    • Export Citation
  • Zhu, Y., and R. E. Newell, 1998: A proposed algorithm for moisture fluxes from atmospheric rivers. Mon. Wea. Rev., 126, 725735, doi:10.1175/1520-0493(1998)126<0725:APAFMF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
Save