Research

Physical factors shaping the probability density function (PDF) of \(T_{2m}\)

Temperature extremes affect human mortality, agricultural yields, and wildfires. Changes in temperature variability in a changing climate can further modify the odds and intensity of extreme temperature events. Thus, a fundamental understanding of how different physical factors (such as perturbations in land surface properties and atmospheric circulations) affect near-surface air temperature is key for an accurate temperature prediction under different climate states. My postdoc research seeks to improve our understanding of the separate contribution of the “land surface driven” and the “atmospheric driven” portion of temperature variability.

(Left) Temperature distribution from current and future climate (source: ipcc); (Right) Diagram of a variety of physical factors affecting near-surface air temperature.

Further reading:

Westerly Jet and Seasonal Transition of the East Asian Summer Monsoon

The East Asian summer monsoon has a unique seasonality characterized by several distinct intraseasonal stages with abrupt transitions in between. Following the spring rainfall in April/May, the pre-mei-yu starts and intensifies rainfall over southern China. The rain belt then jumps northward in June and forms the Chinese mei-yu, the Korean changma, and the Japanese baiu. The second jump occurs in July, marking the end of mei-yu and the onset of midsummer. The latitudinal position of esterlies impinging on the Tibetan Plateau behaves in a synchronous fashion with the seasonal transition of East Asian summer monsoonal rainfall.

Chiang et al. (2015) proposed a “jet transition hypothesis” that invoked a causal linkage between the latitudinal migration of westerlies across the Tibetan Plateau and the timing and duration of the intraseasonal stages of the East Asian summer monsoon in the past climate. During my Ph.D., I explored this hypothesis across a wide range of scenarios by combining observational analysis, fluid dynamics theory, and climate modeling.

See a nice summary from my advisor John Chiang’s website.

Below figures provide an overview of the climatological seasonal evolution of westerlies and East Asian summer monsoon. Data source (add later).

Westerlies and precipitation in (left) spring rainfall stage and (right) pre-mei-yu stage. Dashed contour denotes regions where surface elevation exceeds 2 km.
Westerlies and precipitation in (left) mei-yu stage and (right) midsummer stage. Dashed contour denotes regions where surface elevation exceeds 2 km.

Further reading:

Stratospheric Northern Annular Mode and Ural Blocking High

The Ural Blocking High is one of the major weather systems that have significant impacts on winter weather and short-term climate variability of North China. The purpose of this project is to study the influence of Northern Hemisphere winter stratospheric circulation anomalies on the Ural Blocking High. We composited the Ural Blocking High relative to positive and negative stratospheric Northern Annular Mode (NAM) phases throughout 1958-2010. During the negative stratospheric NAM phase, the Ural Blocking High has higher frequencies of occurrence, longer life cycle, stronger amplitude, and exerts stronger influences on Northern China. Three-dimensional Eliassen-Palm (E-P) flux analysis demonstrates a stronger vertical component of E-P fluxes in the Ural Mountain region during the negative NAM phase than the positive NAM phase. It suggests that stratospheric circulations during the negative NAM phase favor upward wave propagation and thus the development of the Ural Blocking High. The results here have important implications for medium-range forecasting of winter weather or short-term climate variability in North China.

Further reading: