Search Results

You are looking at 11 - 20 of 85 items for

  • Author or Editor: Wei Chen x
  • All content x
Clear All Modify Search
Wei Huang, Song Feng, Jianhui Chen, and Fahu Chen

Abstract

The Tarim basin (TB) in northwestern China is one of the most arid regions in the middle latitudes, where water is scarce year-round. This study investigates the variations of summer precipitation in the TB and their association with water vapor fluxes and atmospheric circulation. The results suggest that the variations of summer precipitation in the TB are dominated by the water vapor fluxes from the south and east, although the long-term mean water vapor mostly comes from the west. The anomalous water vapor fluxes are closely associated with the meridional teleconnection pattern around 50°–80°E and the zonal teleconnection pattern along the Asian westerly jet in summer. The meridional teleconnection connects central Asia and the tropical Indian Ocean; the zonal teleconnection resembles the “Silk Road pattern.” The two teleconnections lead to negative height anomalies in central Asia and positive height anomalies in the Arabian Sea and India and in northern central China. The anomalous pressure gradient force, caused by these height anomalies, leads to anomalous ascending motion in the TB and brings low-level moisture along the eastern periphery of the Tibetan Plateau and water vapor from the Arabian Sea passing over the Tibetan Plateau to influence precipitation development in the study region.

Full access
Shou-Jun Chen, Ying-Hwa Kuo, Wei Ming, and Hong Ying

Abstract

Severe dust storms frequently occur over northwestern China during spring. They are often associated with strong fronts. In this paper, numerical simulations are performed to examine the effect of dust radiative heating on surface frontogenesis.

The absorption and multiple scattering of the dust are included in an atmospheric radiation scheme. A two-dimensional primitive equation model with 20 levels in the vertical is used for idealized simulations. After a 12-h integration a strong narrow front zone is created below 650 mb. The horizontal potential temperature gradient reaches 6 K (100 km)−1, which is three times as large as that in the initial data. A direct vertical transverse circulation is established along the frontal zone. which is qualitatively similar to the observations.

The results show positive interaction between low-level frontogenesis and dust radiative heating. The adiabatic frontogenesis forcing is enhanced by the feedback of the dust radiative heating. These results suggest that the dust heating can significantly affect mesoscale weather systems in arid and desert regions.

Full access
Fengying Wei, Lei Hu, Guanjun Chen, Qian Li, and Yu Xie

Abstract

A close relationship between sea level pressure (SLP) over East Asia and precipitation indices (PIs) in eastern China was observed in the summers (June–August) of 1850–2008 using singular value decomposition (SVD) analysis. To investigate this relationship over a longer period, the SLP fields were reconstructed back to 1470 based on a mathematical model and the historical precipitation indices of eastern China. A cross-validation test of independent samples suggests that the reconstructed SLPs are statistically acceptable. According to the first three predominant SVD modes of the SLP field, three SLP index series (SLPI1–SLPI3) were developed to quantify the thermodynamic differences among the critical SLP centers of East Asia. Both SLPI1 and SLPI2 are highly correlated with the East Asian summer monsoon index, whereas SLPI3 is related to the index of Eurasian meridional atmospheric circulation. The temporal scales of SLP indices were examined during 1470–2008 using the wavelet power spectra. Results indicate that there is significant variance at a 2–5-yr band in the power spectra of the three SLP indices, suggesting SLPI1–SLPI3 have evident interannual variability. Moreover, the wavelet power spectra of SLPI1 and SLPI2 show significantly higher power at the 8–12-yr scale from 1470 to 1750 and at the 60–90-yr scale after 1750. For SLPI3, besides the interannual variability, it has additional periodical variability of 6–11 and 23–33 yr.

Full access
Yue Sun, Haishan Chen, Siguang Zhu, Jie Zhang, and Jiangfeng Wei

Abstract

Under the background of global warming, the Eurasian warming features evident spatial heterogeneity, and Northeast Asia (NEA) is one of the regions with the most significant summer warming. Based on reanalysis data and the CESM1.2.2 model, we investigated the possible impacts of spring Eurasian snowmelt on recent NEA summer warming and the relevant mechanisms. Results show that increased (decreased) spring snowmelt over East Europe to West Siberia (EEWS) is closely linked to NEA summer warming (cooling). Increased spring snowmelt can wet the soil, weakening surface sensible heating to the atmosphere and cooling the atmosphere. The persistent anomalous soil moisture and surface sensible heat induce geopotential height decrease over EEWS and strengthen the eastward-propagating wave train. Furthermore, positive geopotential height anomalies appear in downstream NEA in summer via the adjustment of the atmospheric circulation. Controlled by the anomalous high-pressure system, the west part of NEA is affected by the southerly warm advection, while the east is affected by adiabatic warming induced by the dominant descending motion. Meanwhile, decreased cloud and increased incident solar radiation over NEA favor summer land surface warming. Model results suggest that CESM1.2.2 can basically reproduce the positive correlation between NEA summer land surface temperature and EEWS spring snowmelt. With the positive spring snowmelt forcing, the simulated positive soil moisture and negative sensible heat anomalies persist from spring to summer over EEWS. Consequently, negative geopotential height anomalies appear over the snowmelt region while positive anomalies occur around Lake Baikal, resulting in evident NEA land surface warming.

Open access
Xiuhong Chen, Xianglei Huang, Norman G. Loeb, and Heli Wei

Abstract

The far-IR spectrum plays an important role in the earth’s radiation budget and remote sensing. The authors compare the near-global (80°S–80°N) outgoing clear-sky far-IR flux inferred from the collocated Atmospheric Infrared Sounder (AIRS) and Clouds and the Earth’s Radiant Energy System (CERES) observations in 2004 with the counterparts computed from reanalysis datasets subsampled along the same satellite trajectories. The three most recent reanalyses are examined: the ECMWF Interim Re-Analysis (ERA-Interim), NASA Modern-Era Retrospective Analysis for Research and Application (MERRA), and NOAA/NCEP Climate Forecast System Reanalysis (CFSR). Following a previous study by X. Huang et al., clear-sky spectral angular distribution models (ADMs) are developed for five of the CERES land surface scene types as well as for the extratropical oceans. The outgoing longwave radiation (OLR) directly estimated from the AIRS radiances using the authors’ algorithm agrees well with the OLR in the collocated CERES Single Satellite Footprint (SSF) dataset. The daytime difference is 0.96 ±2.02 W m−2, and the nighttime difference is 0.86 ±1.61 W m−2. To a large extent, the far-IR flux derived in this way agrees with those directly computed from three reanalyses. The near-global averaged differences between reanalyses and observations tend to be slightly positive (0.66%–1.15%) over 0–400 cm−1 and slightly negative (−0.89% to −0.44%) over 400–600 cm−1. For all three reanalyses, the spatial distributions of such differences show the largest discrepancies over the high-elevation areas during the daytime but not during the nighttime, suggesting discrepancies in the diurnal variation of such areas among different datasets. The composite differences with respect to temperature or precipitable water suggest large discrepancies for cold and humid scenes.

Full access
Wen Wang, Wei Cui, Xiaoju Wang, and Xi Chen

Abstract

The Global Land Data Assimilation System (GLDAS) is an important data source for global water cycle research. Using ground-based measurements over continental China, the monthly scale forcing data (precipitation and air temperature) during 1979–2010 and model outputs (runoff, water storage, and evapotranspiration) during 2002–10 of GLDAS models [focusing on GLDAS, version 1 (GLDAS-1)/Noah and GLDAS, version 2 (GLDAS-2)/Noah] are evaluated. Results show that GLDAS-1 has serious discontinuity issues in its forcing data, with large precipitation errors in 1996 and large temperature errors during 2000–05. While the bias correction of the GLDAS-2 precipitation data greatly improves temporal continuity and reduces the biases, it makes GLDAS-2 precipitation less correlated with observed precipitation and makes it have larger mean absolute errors than GLDAS-1 precipitation for most months over the year. GLDAS-2 temperature data are superior to GLDAS-1 temperature data temporally and spatially. The results also show that the change rates of terrestrial water storage (TWS) data by GLDAS and the Gravity Recovery and Climate Experiment (GRACE) do not match well in most areas of China, and both GLDAS-1 and GLDAS-2 are not very capable of capturing the seasonal variation in monthly TWS change observed by GRACE. Runoff is underestimated in the exorheic basins over China, and runoff simulations of GLDAS-2 are much more accurate than those of GLDAS-1 for two of the three major river basins of China investigated in this study. Evapotranspiration is overestimated in the exorheic basins in China by both GLDAS-1 and GLDAS-2, whereas the overestimation of evapotranspiration by GLDAS-2 is less than that by GLDAS-1.

Full access
Yang Chen, Wei Li, Xiaoling Jiang, Panmao Zhai, and Yali Luo

Abstract

Detecting long-term changes in precipitation extremes over monsoon regions remains challenging due to large observational uncertainty, high internal variability at the regional scale, and climate models’ deficiency in simulating monsoon physics. This is particularly true for Eastern China, as illustrated by limited yet controversial detection results for daily scale precipitation extremes and the lack of detection analysis on hourly scale extremes there. Relying on high-quality gauge observations, two complementary techniques are used to detect the footprint of anthropogenic forcings in observed changes in both hourly and daily scale precipitation extremes across Eastern China. Results show that, scaled with global-mean surface temperature during 1970–2017, the regional-scale intensification nearly doubles the Clausius–Clapeyron rate (C-C; ~6.5% °C−1) for the wettest 10 h in the period and almost triples the C-C rate for the top 10 heaviest daily precipitation extremes. The intensification at both time scales, as well as the resulting increase in frequency, is discernibly stronger and more widespread than expected due to random internal variability. This not only lends supports to the model-based detection of forced trends for daily scale precipitation extremes, but it also suggests that anthropogenic warming has already be intensifying hourly scale precipitation extremes in this monsoon region. The magnitude and detectability of observed changes arise primarily from systematic intensification of non-tropical-cyclone-related precipitation extremes in response to the past warming.

Restricted access
Zhe Li, Huiwen Xue, Jen-Ping Chen, and Wei-Chyung Wang

Abstract

This study investigates the effects of meteorological conditions and aerosols on marine stratocumulus in the southeastern Pacific using the Weather Research and Forecasting (WRF) Model. Two regimes with different temperature and moisture conditions in the finest model domain are investigated. The western regime is around 87°–79°W, while the eastern regime is around 79°–71°W. In both regimes, cloud fraction, liquid water path (LWP), cloud thickness, and precipitation show significant diurnal cycles. Cloud fraction can be 0.83 during the night and down to 0.29 during the day in the western regime. The diurnal cycles in the eastern regime have smaller amplitudes but are still very strong. Stratocumulus properties also differ in the two regimes. Compared to the western regime, the eastern regime has lower temperature, higher relative humidity, and a more coupled boundary layer, leading to higher cloud fraction (by 0.11) and lower cloud-base height. The eastern regime also has lower inversion height that causes lower cloud-top height and thinner clouds and, hence, lower LWP and less precipitation.

Cloud microphysical properties are very sensitive to aerosols in both regimes. Increasing aerosols greatly increase cloud number concentration, decrease cloud effective radius, and suppress precipitation. Cloud macrophysical properties (cloud fraction, LWP) are not sensitive to aerosols in either regime, most notably in the eastern regime where precipitation amount is less. The changes in cloud fraction and LWP caused by changes in aerosol concentrations are smaller than the changes in the diurnal cycle and the spatial variability between the two regimes.

Full access
Rui Wang, Xin Yan, Zhenguo Niu, and Wei Chen

Abstract

Water surface temperature is a direct indication of climate change. However, it is not clear how China’s inland waters have responded to climate change in the past using a consistent method on a national scale. In this study, we used Moderate Resolution Imaging Spectroradiometer (MODIS) data from 2000 to 2015 to study the temporal and spatial variation characteristics of water surface temperature in China using the wavelet transform method. The results showed the following: 1) the freezing date of China inland water has shown a significant delaying trend during the past 16 years with an average rate of −1.5 days yr−1; 2) the shift of the 0°C isotherm position of surface water across China has clear seasonal changes, which first moved eastward about 25° and northward about 15°, and then gradually moved back after the year 2009; 3) during the past 16 years, the 0°C isotherm of China’s surface water has gradually moved north by about 0.09° in the latitude direction and east by about 1° in the longitude direction; and 4) the interannual variation of water surface temperature in 17 lakes of China showed a similar fluctuation trend that increased before 2010, and then decreased. The El Niño and La Niña around 2010 could have impacts on the turning point of the annual variation of water surface temperature. This study validated the response of China’s inland surface water to global climate change and improved the understanding of the wetland environment’s response to climate change.

Restricted access
Changlin Chen, Guihua Wang, Shang-Ping Xie, and Wei Liu

ABSTRACT

The Kuroshio and Gulf Stream, the subtropical western boundary currents of the North Pacific and North Atlantic, play important roles in meridional heat transport and ocean–atmosphere interaction processes. Using a multimodel ensemble of future projections, we show that a warmer climate intensifies the upper-layer Kuroshio, in contrast to the previously documented slowdown of the Gulf Stream. Our ocean general circulation model experiments show that the sea surface warming, not the wind change, is the dominant forcing that causes the upper-layer Kuroshio to intensify in a warming climate. Forced by the sea surface warming, ocean subduction and advection processes result in a stronger warming to the east of the Kuroshio than to the west, which increases the isopycnal slope across the Kuroshio, and hence intensifies the Kuroshio. In the North Atlantic, the Gulf Stream slows down as part of the Atlantic meridional overturning circulation (AMOC) response to surface salinity decrease in the high latitudes under global warming. The distinct responses of the Gulf Stream and Kuroshio to climate warming are accompanied by different regional patterns of sea level rise. While the sea level rise accelerates along the northeastern U.S. coast as the AMOC weakens, it remains close to the global mean rate along the East Asian coast as the intensifying Kuroshio is associated with the enhanced sea level rise offshore in the North Pacific subtropical gyre.

Full access