Search Results

You are looking at 1 - 10 of 73 items for

  • Author or Editor: Hong Wang x
  • Refine by Access: All Content x
Clear All Modify Search
Hong Wang
and
Fubao Sun

Abstract

Stationarity is an assumption that permeates training and practice in water-resource engineering. However, with global change, the validity of stationarity as well as uncertainty of nonstationarity in water-resource planning are being questioned; thus, it is critical to evaluate the stationarity of climate variables, especially precipitation. Based on the continuous observation data of precipitation from 1427 stations across China, 593 efficient grid cells (1° × 1°) are constructed, and the annual precipitation stationarities from 1959 to 2018 are analyzed. The evaluated autocorrelation stationarity indicates that 92.24%–96.12% of the grid cells for an autocorrelation coefficient of lag 1–8 years of precipitation are indistinguishable from 0 [90% confidence level (CL)]. The mean stationarity indicates that 97.47% of the grid cells have a stable mean for 30 years (90% CL); beyond the confidence limits, they are mainly located in the northwest of China, where annual precipitation is less, and the average exceeding range is ±3.78 mm. The long-term observation of annual precipitation in Beijing (1819–2018) and Shanghai (1879–2018) also yields autocorrelation and mean stationarities. There is no significant difference in the annual precipitations between the past 20 years (1999–2018) and the past 60 years (1959–2018) over China. Therefore, the annual precipitation in China exhibits a weak stationary behavior that is indistinguishable from the stationary stochastic process. The average variation in precipitation is ±9.55% between 30 successive years and 16.53% between 10 successive years. Therefore, it is valuable and feasible to utilize the historical data of annual precipitation as the basis of water-resources application.

Free access
Run Wang
and
Hong-Li Ren

Abstract

El Niño–Southern Oscillation (ENSO) events exhibit a diversity of amplitudes, spatial patterns, and life cycles, with the main ENSO periods concentrated in the 3–7-yr [low-frequency (LF)] and 2–3-yr [quasi-biennial (QB)] bands. In this study, the spatiotemporal diversity of ENSO is quantitatively examined by extracting the two ENSO modes, namely, the LF and QB components of ENSO, from the traditional Niño-3.4 index and connecting them with the spatial types of ENSO. El Niño events can be regrouped as the QB-dominated central-Pacific ENSO-like (QB-CP), LF-dominated eastern-Pacific ENSO-like (LF-EP), and LF-dominated mixing (LF-mixing) types. La Niña events with vague spatial patterns can also have the same categorization. The QB-CP and LF-EP El Niño types both have a high-amplitude QB component. Meanwhile, the former is less affected by its powerless LF component, but the latter is controlled by its strong LF component. Ocean dynamics of the two El Niño types are distinct from each other. The thermocline feedback dominates the growth of the two El Niño types and contributes to the phase transition of the LF-EP type, while the zonal advective feedback is of increasing importance in the QB-CP El Niño and mainly contributes to the phase transitions of the two El Niño types. Additionally, the LF-mixing type with ambiguous spatial features and complex life cycles is distinguished from the other two types. These results indicate that the two ENSO modes coexist in the tropical Pacific air–sea system, and their combination with changing amplitude is the key to explaining the spatiotemporal diversity of ENSO.

Free access
Hong Wang
,
Fubao Sun
, and
Wenbin Liu

Abstract

Precipitation extremes are expected to increase by 7% per degree of warming according to the Clausius–Clapeyron (CC) relation. However, this scaling behavior is inappropriate for high temperatures and short-duration precipitation extremes. Here, daily data from 702 stations during 1951–2014 and hourly data from 8 stations during 2000–15 are used to examine and explain this behavior in China. Both daily and hourly precipitation extremes exhibit an increase in temperature dependency at lower temperatures. The CC scaling transitions from positive to negative rates with temperatures greater than 25°C. Unlike the increase in daily data, which is similar to single-CC (1CC) scaling, the increase in hourly data resembles super-CC (2CC) scaling for temperatures greater than 13°C. Results show that the precipitation extremes are controlled by water vapor for a given temperature. At lower temperatures, precipitation extremes exhibit a positive linear dependence on daily actual vapor pressure whose value is almost equal to the saturated vapor pressure at a given temperature. At higher temperatures, actual vapor pressure has difficulty maintaining a consistent increasing rate because of the exponential increasing of the saturated vapor pressure. Higher temperatures result in larger vapor pressure deficits, which lead to sharp decreases in precipitation extremes. Similar scaling behaviors are obtained in 10 river basins over China, where the breaking point temperature increases from 17°C along the northwest inland area to 25°C along the southeast coast. These behaviors demonstrate that precipitation extremes are firmly linked to temperature when there is sufficient moisture at lower temperatures and limited by insufficient moisture at higher temperatures. Overall, precipitation extreme events require more attention in a warming climate.

Full access
Haixu Hong
,
Jianqi Sun
, and
Huijun Wang

Abstract

In this study, interannual and interdecadal variations in the extreme high-temperature event (EHE) frequency over northern Asia (NA) and the associated possible mechanisms are explored. On an interannual time scale, the first two empirical orthogonal function modes of the NA EHE frequency exhibit a meridional dipole pattern (EOF1) and diagonal tripolar pattern (EOF2), respectively. The higher NA EHE frequency is related to anomalous local highs, reduced mid- to low clouds, and more solar radiation. The warmer ground further heats the overlying atmosphere through longwave radiation and sensible heat. The warm temperature advection in the lower troposphere and the drier soil conditions also favor higher EHE frequency. Further analysis reveals that the EOF1 mode is related to the Polar–Eurasian teleconnection pattern (POL), while the EOF2 mode is associated with North Atlantic Oscillation (NAO) and Pacific–Japan/East Asia–Pacific pattern (PJ/EAP). The fitted EHE frequency based on the atmospheric factors (POL, NAO, and PJ/EAP) can explain the interannual variation in the regionally averaged EHE frequency by 33.8%. Furthermore, three anomalous sea surface temperature (SST) patterns over the North Atlantic–Mediterranean Sea region and around the Maritime Continent are associated with the two EHE modes by intensifying the pronounced atmospheric teleconnections. Analysis on the simulation of five models in the Atmospheric Model Intercomparison Project experiment further confirms the impact of the pronounced SST patterns on the POL, NAO and PJ/EAP. In addition, NA EHE frequency experienced a significant interdecadal increase around the mid-1990s, which could be associated with the phase shift of the Atlantic multidecadal oscillation and long-term global warming trend.

Full access
Xi Wang
,
Riyu Lu
, and
Xiaowei Hong

Abstract

This study identified that the Silk Road pattern (SRP), which is a teleconnection pattern along the Asian upper-tropospheric westerly jet, becomes significantly weakened in August after the mid-1990s. The SRP in August dominates the upper-tropospheric meridional wind variability over the Eurasian continent before the mid-1990s but does not afterward. Further results suggested that the summer North Atlantic Oscillation (SNAO) and the South Asian rainfall play a role in inducing this decadal weakening of SRP. Before the mid-1990s, the SNAO is stronger and its southern pole is located over northwestern Europe but is weakened and its southern pole shifts southwestward afterward, resulting in the decadal weakening of its contribution to the SRP. In addition, the relationship between the SRP and South Asian rainfall is substantially weakened after the mid-1990s, which also contributes to the weakening of SRP.

Restricted access
Haixu Hong
,
Jianqi Sun
, and
Huijun Wang

Abstract

In this study, the synoptic atmospheric patterns responsible for regional extreme high-temperature events (REHEs) over northern Asia (NA) are investigated. First, a hybrid regionalization approach is applied to the daily maximum temperature (Tmax), and three subregions of NA can be identified: western NA, central NA, and southeastern NA. To better understand the mechanism for the NA REHE formation, the REHE-related synoptic circulation patterns over each subregion are further categorized into two types. These six synoptic circulation patterns influence the NA REHE occurrence through different radiation and advection processes. Generally, the radiation process dominates the NA REHE occurrence, while the horizontal temperature advection plays a more important role in the synoptic dipole patterns than in the monopole high patterns. The heatwaves associated with the six synoptic patterns can last more than 3.8 days, with a maximum of 2 weeks. From the forecasting perspective, six wave trains are explored as the precursors of these six synoptic circulation patterns, separately. The wave trains originate from the North Atlantic Ocean and Europe with at least a 3-day lead and then propagate eastward to NA, exerting influences on the pronounced six synoptic circulation patterns and consequently affecting the NA REHEs. In terms of long-term change, the REHEs over the three subregions show significant increasing trends over 1960–2018 and significant interdecadal increases around the mid-1990s, in which the contribution of each synoptic pattern–related REHE is different.

Restricted access
Haixu Hong
,
Jianqi Sun
, and
Huijun Wang

Abstract

This study investigates the spatial–temporal variations in summer extreme precipitation event (EPE) frequency over northern Asia and related atmospheric circulations. The division analysis indicates that three subregions of western Siberia (WS), eastern Siberia (ES), and eastern Mongolia–northeastern China can be identified, and the EPE variations over WS and ES are focused on here. On an interannual time scale, higher EPE frequencies are related to a similar dipole pattern in the upper troposphere [anomalous cyclone (anticyclone) to the west (southeast) of these two subregions] and a local anomalous cyclone in the lower troposphere. The dipole pattern leads to anomalous air divergence in the upper troposphere and compensating ascending motion over the subregions; the local anomalous cyclone in the lower troposphere leads to water vapor convergence. These anomalous atmospheric circulations therefore provide favorable dynamic and moisture conditions for higher EPE frequencies. Further analysis indicates that the WS EPE frequency is influenced by the combination of polar–Eurasian (POL) and North Atlantic Oscillation (NAO) patterns, while the ES EPE frequency is influenced by Scandinavian (SCAND) [British–Baikal Corridor (BBC)] pattern over 1987–2004 (2005–15). The alternate influence on the ES EPE frequency may result from the interdecadal change in the structure of SCAND and BBC patterns. In addition, the East Asian summer monsoon (EASM) shows enhanced influence on ES EPE frequency after the late 1990s, which could be due to interdecadal strengthening and extending of the anomalous cyclone around Lake Baikal. This cyclone is concurrent with EASM, and its changes favor water vapor transported by EASM to ES after the late 1990s.

Full access
Haixu Hong
,
Jianqi Sun
, and
Huijun Wang

Abstract

This study investigates the spatial–temporal variations in summer extreme precipitation event (EPE) frequency over northern Asia and related atmospheric circulations. The division analysis indicates that three subregions of western Siberia (WS), eastern Siberia (ES), and eastern Mongolia–northeastern China can be identified, and the EPE variations over WS and ES are focused on here. On an interannual time scale, higher EPE frequencies are related to a similar dipole pattern in the upper troposphere [anomalous cyclone (anticyclone) to the west (southeast) of these two subregions] and a local anomalous cyclone in the lower troposphere. The dipole pattern leads to anomalous air divergence in the upper troposphere and compensating ascending motion over the subregions; the local anomalous cyclone in the lower troposphere leads to water vapor convergence. These anomalous atmospheric circulations therefore provide favorable dynamic and moisture conditions for higher EPE frequencies. Further analysis indicates that the WS EPE frequency is influenced by the combination of polar–Eurasian (POL) and North Atlantic Oscillation (NAO) patterns, while the ES EPE frequency is influenced by Scandinavian (SCAND) [British–Baikal Corridor (BBC)] pattern over 1987–2004 (2005–15). The alternate influence on the ES EPE frequency may result from the interdecadal change in the structure of SCAND and BBC patterns. In addition, the East Asian summer monsoon (EASM) shows enhanced influence on ES EPE frequency after the late 1990s, which could be due to interdecadal strengthening and extending of the anomalous cyclone around Lake Baikal. This cyclone is concurrent with EASM, and its changes favor water vapor transported by EASM to ES after the late 1990s.

Full access
Yao Feng
,
Hong Wang
,
Wenbin Liu
, and
Fubao Sun

Abstract

Soil moisture (SM) during the vegetation growing season largely affects plant transpiration and photosynthesis, and further alters the land energy and water balance through its impact on the energy partition into latent and sensible heat fluxes. To highlight the impact of strong vegetation activity, we investigate global SM–climate interactions over the peak growing season (PGS) during 1982–2015 based on multisource datasets. Results suggest widespread positive SM–precipitation (P), SM–evapotranspiration (ET), and negative SM–temperature (T) interactions with non-negligible negative SM–P, SM–ET, and positive SM–T interactions over PGS. Relative to the influence of individual climate factors on SM, the compounding effect of climate factors strengthens SM–climate interactions. Simultaneously, variations of SM are dominated by precipitation from 50°N toward the south, by evapotranspiration from 50°N toward the north, and by temperature over the Sahara, western and central Asia, and the Tibetan Plateau. Importantly, the higher probability of concurrent SM wetness and climate extremes indicates the instant response of SM wetness to extreme climate. In contrast, the resistance of vegetation partially contributes to a consequent slower response of SM dryness to extreme climate. We highlight the significance of the compounding effects of climate factors in understanding SM–climate interaction in the context of strong vegetation activity, and the response of SM wetness and dryness to climate extremes.

Free access
Xu Yue
,
Huijun Wang
,
Hong Liao
, and
Dabang Jiang

Abstract

The climatic responses to the direct radiative effect of dust aerosol at the Last Glacial Maximum (LGM) are examined using a general circulation model with online simulation of dust. The predicted global dust emission at the LGM is 2.3 times as large as the present-day value, which is the combined effect of the expansion of dust sources and the favorable meteorological parameters (MPs; e.g., the strong surface wind and the low air humidity) under the LGM climate. Simulated global dust emission is 1966 Tg yr−1 with present-day dust sources and MPs, 2820 Tg yr−1 with LGM dust sources and current MPs, 2599 Tg yr−1 with present-day dust sources and LGM MPs, and 4579 Tg yr−1 with LGM sources and MPs. The simulated percentage increases of dust concentrations are the largest at high latitudes in both hemispheres, which are consistent with the deposition data from geological records. The LGM dust is estimated to exert global annual-mean shortwave (SW) and longwave (LW) radiative forcing (RF) of −4.69 and +1.70 W m−2 at the surface, respectively, and −0.58 and +0.68 W m−2 at the top of the atmosphere, respectively. On a global- and annual-mean basis, surface air temperature (SAT) is predicted to be reduced by 0.18 K and precipitation is reduced by 0.06 mm day−1, as a result of the net (SW and LW) radiative effect of dust at the LGM. Two sensitivity studies are performed to identify the uncertainties in simulated climatic effect of LGM dust that arise from the assumed LW and/or SW absorption by dust: 1) in the absence of dust LW radiative effect, the LGM global- and annual-mean SAT is predicted to be further reduced by 0.19 K; and 2) when the single scattering albedo of the Saharan dust at 0.55 μm is increased from 0.89 to 0.98 in the LGM climate simulation, the LGM dust-induced annual- and global-mean surface cooling increases from 0.18 to 0.63 K even with both SW and LW radiative effects of dust. In these two sensitivity studies, the LGM dust is predicted to induce an average cooling of 0.42 and 0.72 K in SAT, respectively, over the tropical oceans.

Full access