Search Results

You are looking at 1 - 10 of 19 items for

  • Author or Editor: Jun Matsumoto x
  • All content x
Clear All Modify Search
Tomoshige Inoue and Jun Matsumoto

Abstract

Interdecadal climate changes occurring during the latter half of August (LA) in central Japan are described, and the associated changes in rainfall, typhoon tracks, and circulation patterns over East Asia and the western North Pacific (WNP) regions are investigated. Since 1984, rates of sunshine and temperature have increased, while rainfall has decreased significantly during LA in central Japan. In contrast, rainfall over the Southwest Islands, northern part of Taiwan, and in the south of the middle and lower reaches of the Yangtze River in China has increased. Changes in the positions and tracks of typhoons are responsible for these changes. Prior to 1983, many typhoons approached the central-western part of Japan during LA, while after 1984, most typhoons were deflected away from Japan and moved northwestward to Taiwan and China. The North Pacific subtropical high during LA extended more westward after 1984, which affected the interdecadal changes in sunshine, temperature, rainfall, and typhoon tracks, not only in central Japan, but also over East Asia and the WNP regions.

Full access
Satoru Yokoi and Jun Matsumoto

Abstract

This paper reveals synoptic-scale atmospheric conditions over the South China Sea (SCS) that cause heavy rainfall in central Vietnam through case study and composite analyses. The heavy rainfall event discussed in this study occurred on 2–3 November 1999. Precipitation in Hue city (central Vietnam) was more than 1800 mm for these 2 days. Two atmospheric disturbances played key roles in this heavy rainfall. First, a cold surge (CS) northerly wind anomaly in the lower troposphere, originating in northern China near 40°N, propagated southward to reach the northern SCS and then lingered there for a couple of days, resulting in stronger-than-usual northeasterly winds continuously blowing into the Indochina Peninsula against the Annam Range. Second, a southerly wind anomaly over the central SCS, associated with a tropical depression–type disturbance (TDD) in southern Vietnam, seemed to prevent the CS from propagating farther southward. Over the northern SCS, the southerly wind anomaly formed a strong low-level convergence in conjunction with the CS northeasterly wind anomaly, and supplied warm and humid tropical air. These conditions induced by the CS and TDD are favorable for the occurrence of the heavy orographic rainfall in central Vietnam. The TDD can be regarded as a result of a Rossby wave response to a large-scale convective anomaly over the Maritime Continent associated with equatorial intraseasonal variability.

Using a 24-yr (1979–2002) reanalysis and surface precipitation datasets, the authors confirm that the coexistence of the CS and TDD is important for the occurrence of heavy precipitation in central Vietnam. In addition, it is observed that CSs without a TDD do not lead to much precipitation.

Full access
Satoru Yokoi, Takehiko Satomura, and Jun Matsumoto

Abstract

With the use of daily rain gauge data observed at 210 stations in the Indochina Peninsula (ICP) for the 26 yr from 1978 to 2003, this paper describes climatological characteristics of 2 types of intraseasonal variations (ISVs): the 30–60-day variation (30–60DV) and the 10–20-day variation (10–20DV). The authors find that these characteristics are quite different from place to place in the ICP.

During the rainy season, variance of the 30–60DV is generally larger in coastal regions than over inland regions and it has two local maxima: one found in the coastal region of Myanmar (CMY) and the other in the southern Laos and central Vietnam region (SLCV). Wavelet analysis reveals that the 30–60DV in the CMY is active throughout the rainy season (May–October) and exhibits the maximum activity in May–June. In addition, its typical time scale shifts from 40 days in the early half of the rainy season to 50 days in the latter half. Cross-correlation analysis reveals that its signal propagates northward. On the other hand, the 30–60DV in the SLCV is active only during July–October, and its signal propagates northwestward.

The largest variance of the 10–20DV is found in the coastal regions of northern and central Vietnam (CNCV), while the variance in other coastal regions is generally smaller than that in inland regions. In contrast to the 30–60DV, the 10–20DV activity varies significantly over the course of the rainy season. The 10–20DV in the inland regions is active in May and September and inactive in July, while that in the CNCV is active during August–November. The 10–20DV exhibits high spatial coherence over most of the ICP, and its signal propagates west-northwestward.

Relationship of the ISV in the ICP with synoptic-scale ISV structures is also discussed.

Full access
Marcelino Q. Villafuerte II and Jun Matsumoto

Abstract

This study investigates the changes in annual and seasonal maximum daily rainfall (RX1day) in Southeast Asia, obtained from gauge-based gridded precipitation data, to address the increasing concerns about climate change in the region. First, the nonparametric Mann–Kendall test was employed to detect significant trends in RX1day. Then, maximum likelihood modeling, which allows the incorporation of covariates in the location parameter of the generalized extreme value (GEV) distribution, was conducted to determine whether the rising global mean temperature, as well as El Niño–Southern Oscillation (ENSO), is influencing extreme rainfall over the region. The findings revealed that annual and seasonal RX1day is significantly increasing in Indochina and east-central Philippines while decreasing in most parts of the Maritime Continent during the past 57 yr (1951–2007). The trends in RX1day were further linked to the rising global mean temperature. It was shown that the location parameter of the GEV—and hence the RX1day on average—has significantly covaried with the annually averaged near-surface global mean temperature anomaly. Such covariation is pronouncedly observed over the regions where significant trends in RX1day were detected. Furthermore, the results demonstrated that, as ENSO develops in July–September, negative covariations between the location parameter of the GEV and the ENSO index, implying a higher (lower) likelihood of extreme rainfall during La Niña (El Niño), were observed over the Maritime Continent. Such conditions progress northward to the regions of Indochina and the Philippines as ENSO approaches its maturity in October–December and then retreat southward as the ENSO weakens in the ensuing seasons.

Full access
Tsing-Chang Chen, Jenq-Dar Tsay, and Jun Matsumoto

Abstract

A northwest–southeast-oriented summer monsoon trough exists between northern Indochina and northwestern Borneo. Ahead of this the South China Sea (SCS) trough is located at a convergent center west of the Philippines, which provides an environment favorable for rain-producing synoptic systems to produce rainfall over this center and form the SCS summer rainfall center. Revealed from the xt diagram for rainfall, this rainfall center is developed by multiple-scale processes involved with the SCS trough (TR), tropical depression (TY), interaction of the SCS trough with the easterly wave/tropical depression (EI), and easterly wave (EW). It is found that 56% of this rainfall center is produced by the SCS trough, while 41% is generated by the other three synoptic systems combined. Apparently, the formation of the SCS summer monsoon rainfall center is contributed to by these four rain-producing synoptic systems from the SCS and the Philippines Sea. The Southeast Asian summer monsoon undergoes an interannual variation and exhibits an east–west-oriented cyclonic (anticyclonic) anomalous circulation centered at the western tropical Pacific east of the Luzon Strait. This circulation change is reflected by the deepening (filling) of the SCS summer monsoon trough, when the monsoon westerlies south of 15°N intensify (weaken). This interannual variation of the monsoon westerlies leads to the interannual variation of the SCS summer monsoon rainfall center to follow the Pacific–Japan oscillation of rainfall. The rainfall amount produced over this rainfall center during the weak monsoon season is about two-thirds of that produced during the strong monsoon season. The rain-production ratio between TR and TY + EI + EW is 60:38 during the strong monsoon season and 47:49 during the weak monsoon season.

Full access
Tsing-Chang Chen, Jenq-Dar Tsay, Jun Matsumoto, and Jordan Alpert

Abstract

After the onset of the Southeast Asian summer monsoon in mid-May, the South China Sea (SCS) trough is deepened by the intensified monsoon westerlies to facilitate the development of a synoptic cyclonic shear flow. This shear flow forms an environment favorable for the SCS tropical storm (TS)/typhoon (TY) genesis triggered by the surge of this monsoon circulation. This genesis mechanism has not been well documented. Seventeen named SCS TS/TY geneses in May over 1979–2016 occurred under the following environmental conditions/processes: 1) with its maximum located south of 15°N, the intensified monsoon westerlies are extended eastward beyond 120°E, 2) the synoptic SCS cyclonic shear flow is developed by the tropical easterlies fed by a northeast Asian cold surge (or a North Pacific cold-air outbreak) and the intensified monsoon westerlies, and 3) SCS TS/TY genesis is triggered by the surge of monsoon flow. The accuracy of the monthly mean forecasts is limited. However, it is found that SCS TS/TY genesis only occurs after the existence of persistent, strong, monsoon westerlies lasting for at least 5 days. Forecasts from the National Centers for Environmental Prediction Global Forecast System (2004–16) and the Global Ensemble Forecast System (1985–2003) cover these 15 SCS TS/TY geneses. The requirements for SCS TS/TY genesis in May described above are met by the 5-day-mean Southeast Asian summer monsoon circulation. Based on a statistical analysis of 5-day forecasts for these TS/TY geneses, a four-step forecast advisory is introduced. The forecasts for SCS TS/TY genesis can be made 3 days prior to occurrence.

Full access
Shin-Ya Ogino, Manabu D. Yamanaka, Shuichi Mori, and Jun Matsumoto

Abstract

Motivated by observational evidence of rainfall concentrations near tropical coastlines with a diurnal cycle, the annual mean precipitation amount was quantified in the tropics (latitudes lower than 37°) obtained as a function of coastal distance and compared between land and ocean sides. The data are from the Tropical Rainfall Measuring Mission (TRMM). Precipitation amount peaks at the coastline and decreases rapidly over a distance of 300 km from the coastline on both sides of the coastline. The precipitation inside the “coastal region” (defined by a distance <300 km from the coastline) accounts for approximately 34% of the total over the entire tropics, while that outside the coastal region accounts for 52% and 14% on the ocean and land sides, respectively. Since the coastal regions are about 29% of the total tropical areas, the precipitation per unit area inside the coastal regions is higher than that outside. Examining the grid number variation in the coastal regions with respect to the annual precipitation amount resulted in the finding that more than 90% of the annual precipitation with the amount of 3500 mm yr−1 or more occurs exclusively in the coastal regions, indicating that precipitation systems unique to coastal regions are needed for producing the highest annual precipitation on Earth.

Full access
Tsing-Chang Chen, Jenq-Dar Tsay, Jun Matsumoto, and Jordan Alpert

Abstract

The peak intensity occurrence frequency over the life cycles of parent cold-surge vortices (CSVs) for heavy rainfall/flood (HRF) events is classified into two types depending on their life cycles having two or three peak intensities, denoted as HRF2 or HRF3, respectively. The formation of an HRF2 event from its parent CSV(HRF2) formation is ≤5 days, while the formation of an HRF3 event is ≥6 days. The latter group contributes ~57% of the total number of HRF events. As a result of some model constraints, the formation and development of HRF3 events are not well forecasted by the Global Forecast System (GFS) and regional forecast models. The life cycle and second peak intensity for CSV(HRF3) allow for the introduction of a forecast advisory for HRF3 events. Identification of CSVs and two sufficient requirements for the formation and occurrence of HRF events were developed by previous studies. Nevertheless, two new necessary steps are now included in the proposed forecast advisory. The population ratio for CSV(HRF3) and the regular CSV is only about 15%. The occurrence optimum time t o for the CSV(HRF3) second peak intensity from this vortex formation is about 3 days 6 h. The GFS forecast over t o is utilized to identify CSV(HRF3). Then, the relay of the GFS forecast from the occurrence time of the CSV(HRF3) second peak is used to predict the formation/occurrence of HRF3 events. Six HRF3 events during cold seasons for 2013–16 are used to test the feasibility of this forecast advisory. Results clearly demonstrate this advisory is a success for the forecast of HRF3 events over the entire life cycles of their parent CSV(HRF3)s.

Full access
Tsing-Chang Chen, Jenq-Dar Tsay, and Jun Matsumoto

Abstract

During 15 November–31 December, a cold-season rainfall center appears in the southern part of the South China Sea (SCS) north of northwestern Borneo and juxtaposed along the southwest–northeast direction with rainfall centers for the Malay Peninsula and the Philippines. This SCS rainfall center also coincides geographically with the SCS surface trough. An effort is made to explore the formation mechanism of this rainfall center. It is primarily formed by the second intensification of heavy rainfall/flood cold surge vortex [CSV(HRF)] through its interaction with a cold surge flow over the SCS trough. Both the SCS rainfall center and the SCS surface trough are located at the easterly flow north of the near-equator trough. Modulated by the interannual variation of the cyclonic shear flow along the near-equator trough in concert with the El Niño–Southern Oscillation (ENSO) cycle, the SCS rainfall center undergoes an interannual variation. The impact of this ENSO cycle is accomplished through the regulation of CSV(HRF) trajectories originating from the Philippines vicinity and Borneo and propagating to different destinations. Rain-producing efficiency determined by the interannual variation of the divergent circulation accompanies the cyclonic shear flow around the near-equator trough in response to this ENSO cycle.

Full access
Dzung Nguyen-Le, Jun Matsumoto, and Thanh Ngo-Duc

Abstract

The onset dates of rainy season over the eastern Indochina Peninsula (8.5°–23.5°N, 100°–110°E) are objectively determined for individual years from 1958 to 2007 using the empirical orthogonal function (EOF) analysis. On average, the onset of the summer rainy season (SRS) determined by EOF1 is 6 May, with a standard deviation of 13 days. The autumn rainy season (ARS) indicated by EOF2 has a mean onset and standard deviation of 16 September and 12 days, respectively. The SRS onset is characterized by the evolution of summer monsoon westerlies and the northward propagation of strong convection from the equatorial region. Conversely, the withdrawal of the summer monsoon over northeastern Indochina in late summer–early autumn favors the ARS onset. Both onsets are strongly associated with intraseasonal oscillation on 30–60- and 10–20-day time scales.

Examination of the precursory signals associated with the early/late onsets of both SRS and ARS implies that ENSO has a significant impact on their year-to-year variations. In La Niña years, the subsequent SRS tends to have early onsets. Simultaneously, the western Pacific subtropical high (WPSH) weakens and retreats eastward earlier. In contrast, advanced ARS onset generally occurs during an El Niño–developing autumn with weakened equatorial easterlies and suppressed convection over the central Indian Ocean from the preceding summer, as evident in weakened Walker circulation. However, robust precursory signals in SST are observed only from midsummer (July–August). An earlier ARS onset is also associated with the development of an anomalous Philippine Sea anticyclone and a westward-extended WPSH from midsummer. However, no coherent correlation is found between the late onset and La Niña.

Full access