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Wenhao Dong

I have broad interests in model diagnostic, the variability of large-scale circulation and changes in regional precipitation, tropical disturbance (low-pressure systems, mesoscale convective systems, etc.), and environmental data analysis.



Projected changes in Indian monsoon low-pressure system

Track density of MLPSs
Precipitation associated with MLPSs


Monsoon low-pressure systems (MLPSs) are among the most important synoptic-scale disturbances of the South Asian summer monsoon. Potential changes in their characteristics in a warmer climate would have broad societal impacts. Yet, the findings from a few existing studies are inconclusive. We use the Geophysical Fluid Dynamics Laboratory (GFDL) coupled climate model CM4.0 to examine the projected changes in the simulated MLPS activity under a future emission scenario. It is shown that CM4.0 can skillfully simulate the number, genesis location, intensity, and lifetime of MLPSs. Global warming gives rise to a significant decrease in MLPS activity. An analysis of several large-scale environmental variables, both dynamic and thermodynamic, suggests that the decrease in MLPS activity can be attributed mainly to a reduction in low-level relative vorticity over the core genesis region. The decreased vorticity is consistent with weaker large-scale ascent, which leads to less vorticity production through the stretching term in the vorticity equation. Assuming a fixed radius of influence, the projected reduction in MLPSs would significantly lower the associated precipitation over north-central India, despite an overall increase in mean precipitation.

Relevant Publications:

Warm-and-dry biases over the central U.S.

Correspondence between precipitation bias and temperature bias
Dependence of temperature change on temperature bias

Climate models show a conspicuous summer warm and dry bias over the central United States. Using results from 19 climate models in the Coupled Model Intercomparison Project Phase 5 (CMIP5), we report a persistent dependence of warm bias on the dry bias with the precipitation deficit leading the warm bias over this region. The precipitation deficit is associated with the widespread failure of models in capturing strong rainfall events in summer over the central U.S. A robust linear relationship between the projected warming and the present-day warm bias enables us to empirically correct future temperature projections. By the end of the 21st century under the RCP8.5 scenario, the corrections substantially narrow the intermodel spread of the projections and reduce the projected temperature by 2.5 K, resulting mainly from the removal of the warm bias. Instead of a sharp decrease, after this correction, the projected precipitation is nearly neutral for all scenarios.

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Up-and-over moisture transport

Schematic plot of up-and-over moisture transport and upslope moisture transport
Precipitation and mid-level circulation anomalies averaged over LPS days and non-LPS days

During my Ph.D. study, I am interested in the rainfall connection between the Indian subcontinent and the Tibetan Plateau. We find that more than 60% of total summer rainfall over the southwestern Tibetan Plateau (SWTP) is related to the low-pressure system (LPS) occurrence over the Indian subcontinent. LPSs are associated with a 15% rise in average daily rainfall and a 10% rise in rainy days over the SWTP. We proposed that this relationship is maintained primarily through up‐and‐over transport, in which convectively lifted moisture over the Indian subcontinent is swept over the SWTP by southwesterly winds in the middle troposphere.

LPSs play two roles in supplying up‐and‐over moisture transport. First, these systems elevate large amounts of water vapor and condensed water to the mid-troposphere. Second, the circulations associated with LPSs interact with the background westerlies to induce southwesterly flow in the mid-troposphere, transporting elevated moisture and condensate over the Himalayan Mountains. Our findings indicate that LPSs are influential in extending the northern boundary of the South Asian monsoon system across the Himalayas into the interior of the SWTP. The strength of this connection depends on both LPS characteristics and the configuration of the mid-tropospheric circulation, particularly the prevailing westerlies upstream of the SWTP.

Relevant Publications:

Warm-season rainfall change over arid eastern-central Asia

Variability of precipitation over the AECA
Linear trends of precipitation, soil moisture, and NDVI

Multiple studies have reported a shift in the trend of warm-season rainfall over arid eastern–central Asia (AECA) around the turn of the new century, from increasing over the second half of the twentieth century to decreasing during the early years of the twenty-first. Here, a closer look based on multiple precipitation datasets reveals important regional disparities in these changes. Warm-season rainfall increased over basin areas but decrease significantly over mountain ranges in the past decades. This discrepancy, which is also reflected in changes in river flow, soil moisture, and vegetation, primarily results from disparate responses to enhanced warming in the mountain and basin areas of AECA.

In addition to changes in the prevailing circulation and moisture transport patterns, the decrease in precipitation over the mountains has occurred mainly because increases in local water vapor saturation capacity (which scales with temperature) have outpaced the available moisture supply, reducing relative humidity and suppressing precipitation. By contrast, rainfall over basin areas has been maintained by accelerated moisture recycling driven by rapid glacier retreat, snowmelt, and irrigation expansion. This trend is unsustainable and is likely to reverse as these cryospheric buffers disappear, with potentially catastrophic implications for local agriculture and ecology.

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