A Multiscale Analysis of the Extreme Weather Events over Western Russia and Northern Pakistan during July 2010

2012 ◽  
Vol 140 (5) ◽  
pp. 1639-1664 ◽  
Author(s):  
Thomas J. Galarneau ◽  
Thomas M. Hamill ◽  
Randall M. Dole ◽  
Judith Perlwitz
Keyword(s):  
Tibetan Plateau ◽  
Heat Wave ◽  
Multiscale Analysis ◽  
Large Scale ◽  
The Tibetan Plateau ◽  
Northern Pakistan ◽  
Key Factors ◽  
Energy Dispersion ◽  
Low Level ◽  
Low Level Jet

Abstract This manuscript presents a detailed multiscale analysis—using observations, model analyses, and ensemble forecasts—of the extreme heat wave over Russia and historic floods over Pakistan during late July 2010, with an emphasis on the floods over northern Pakistan. The results show that recirculation of air and dynamically driven subsidence occurring with the intensification of the blocking anticyclone in late July 2010 were key factors for producing the exceptionally warm temperatures over western Russia. Downstream energy dispersion from the blocking region led to trough deepening northwest of Pakistan and ridge building over the Tibetan Plateau, thereby providing the linkage between the Russian heat wave and Pakistan flood events on the large scale, in agreement with previous studies. The extratropical downstream energy dispersion and enhanced convective outflow on the large scale associated with the active phase of the Madden–Julian oscillation facilitated the formation of an intense upper-level jet northwest of Pakistan. During this same period an intense southeasterly, low-level, barrier jet–like feature formed over northern Pakistan in conjunction with a westward-moving monsoon depression. This low-level jet and deep easterly flow on the equatorward flank of an anomalous anticyclone over the Tibetan Plateau further enhanced the transport of deep tropical moisture into Pakistan and produced a sustained upslope flow and an extended period of active convection, thereby providing an important contribution leading to the exceptional rainfall amounts. The deep easterly flow and intense low-level jet were features that were absent during previous convective episodes over northern Pakistan in 2010, and hence, were likely key factors in the increased severity of the late July event.

Dynamic and Thermodynamic Relations of Distinctive Stratus Clouds on the Lee Side of the Tibetan Plateau in the Cold Season

2013 ◽  
Vol 26 (21) ◽  
pp. 8378-8391 ◽  
Author(s):  
Yi Zhang ◽  
Rucong Yu ◽  
Jian Li ◽  
Weihua Yuan ◽  
Minghua Zhang
Keyword(s):  
Tibetan Plateau ◽  
Large Scale ◽  
Eastern China ◽  
Cold Season ◽  
Water Vapor Transport ◽  
The Tibetan Plateau ◽  
Primary Role ◽  
Moist Air ◽  
Low Level ◽  
Stratus Clouds

Abstract Given the large discrepancies that exist in climate models for shortwave cloud forcing over eastern China (EC), the dynamic (vertical motion and horizontal circulation) and thermodynamic (stability) relations of stratus clouds and the associated cloud radiative forcing in the cold season are examined. Unlike the stratus clouds over the southeastern Pacific Ocean (as a representative of marine boundary stratus), where thermodynamic forcing plays a primary role, the stratus clouds over EC are affected by both dynamic and thermodynamic factors. The Tibetan Plateau (TP)-forced low-level large-scale lifting and high stability over EC favor the accumulation of abundant saturated moist air, which contributes to the formation of stratus clouds. The TP slows down the westerly overflow through a frictional effect, resulting in midlevel divergence, and forces the low-level surrounding flows, resulting in convergence. Both midlevel divergence and low-level convergence sustain a rising motion and vertical water vapor transport over EC. The surface cold air is advected from the Siberian high by the surrounding northerly flow, causing low-level cooling. The cooling effect is enhanced by the blocking of the YunGui Plateau. The southwesterly wind carrying warm, moist air from the east Bay of Bengal is uplifted by the HengDuan Mountains via topographical forcing; the midtropospheric westerly flow further advects the warm air downstream of the TP, moistening and warming the middle troposphere on the lee side of the TP. The low-level cooling and midlevel warming together increase the stability. The favorable dynamic and thermodynamic large-scale environment allows for the formation of stratus clouds over EC during the cold season.

scholarly journals Diagnostic analysis of a regional heavy snowfall event over the Tibetan Plateau using NCEP reanalysis data and WRF

2021 ◽  
Author(s):  
Lian Liu ◽  
Yaoming Ma ◽  
Nan Yao ◽  
Weiqiang Ma
Keyword(s):  
Water Vapor ◽  
Tibetan Plateau ◽  
Large Scale ◽  
Stable Stratification ◽  
Reanalysis Data ◽  
The Tibetan Plateau ◽  
Diagnostic Analysis ◽  
Heavy Snowfall ◽  
Low Level ◽  
Snowfall Event

AbstractSnowstorms frequently occur in spring over the heterogeneous underlying surface of the Tibetan Plateau, causing both economic and societal damage. What the intensity of factors triggering snowstorms remains poorly understood. This study quantitatively diagnoses water vapor, the thermodynamic and dynamic conditions of a large-scale heavy snowfall event over the Tibetan Plateau using reanalysis data. Here we show, a cold vortex, the Southern Branch Trough and a meridional shear line are favorable synoptic systems. The snowfall is characterized by low-layer (− 8.3 × 10−7 g s−1 hPa−1 cm−2) and whole-layer (− 4.5 × 10−4 g s−1 cm−2) moisture convergence, low-level atmospheric convergence and high-level divergence (± 3 × 10−4 s−1), low-level positive vorticity (4.8 × 10−4 s−1) and strong vertical velocity (− 4 Pa s−1). Although the convectively-stable stratification acted to suppress snowfall, the abundant water vapor and strong orographic uplift of Himalayas and the downhill wind speed convergence overcome this to trigger the heavy snowfall event witnessed in March 2017. These diagnostic results are well consistent with those from WRF simulation. Our study acknowledges the importance of WRF in diagnostic analysis, deepens the understanding of evolution mechanisms and provides theoretical references for accurate forecasting of such events over the Tibetan Plateau. It would aid the development of effective strategies for sustainable livestock, and the mitigation and prevention of snow disasters in this region.

The Effects of Midlatitude Waves over and around the Tibetan Plateau on Submonthly Variability of the East Asian Summer Monsoon

2009 ◽  
Vol 137 (7) ◽  
pp. 2286-2304 ◽  
Author(s):  
Hatsuki Fujinami ◽  
Tetsuzo Yasunari
Keyword(s):  
Tibetan Plateau ◽  
Rossby Wave ◽  
Large Scale ◽  
Southern China ◽  
Phase Speed ◽  
The Tibetan Plateau ◽  
Low Level ◽  
Zonal Wavenumber ◽  
Upper Level ◽  
Southward Migration

Convective variability at submonthly time scales (7–25 days) over the Yangtze and Huaihe River basins (YHRBs) and associated large-scale atmospheric circulation during the mei-yu season were examined using interpolated outgoing longwave radiation (OLR) and NCEP–NCAR reanalysis data for 12 yr having active submonthly convective fluctuation over the YHRBs within the period 1979–2004. Correlations between convection anomalies over the YHRBs and upper-level streamfunction anomalies at every grid point show two contrasting patterns. One pattern exhibits high correlations along the northern to eastern peripheries of the Tibetan Plateau (defined as the NET pattern), whereas the other has high correlations across the Tibetan Plateau (defined as the AT pattern). Composite analysis of the NET pattern shows slow southward migration of convection anomalies from the northeastern periphery of the Tibetan Plateau to southern China, in relation to southward migration of the mei-yu front caused by simultaneous amplification of upper- and low-level waves north of the YHRBs. In the AT pattern, convection anomalies migrate eastward from the western Tibetan Plateau to the YHRBs. A low-level vortex is created at the lee of the plateau by eastward-moving upper-level wave packets and associated convection from the plateau. Rossby wave trains along the Asian jet characterize the upper-level circulation anomalies in the two patterns. The basic state of the Asian jet during the mei-yu season differs between the two patterns, especially around the Tibetan Plateau. The Asian jet has a northward arclike structure in NET years, while a zonal jet dominates in AT years. These differences could alter the Rossby wave train propagation route. Furthermore, the larger zonal wavenumber of AT waves (∼7–8) than of NET waves (∼6) means faster zonal phase speed relative to the ground in the AT pattern than in the NET pattern. These differences likely explain the meridional amplification of waves north of the YHRBs in the NET pattern and the eastward wave movement across the plateau in the AT pattern.

scholarly journals The Role of Shallow Convection over the Tibetan Plateau

2017 ◽  
Vol 30 (15) ◽  
pp. 5791-5803 ◽  
Author(s):  
Yunying Li ◽  
Minghua Zhang
Keyword(s):  
Tibetan Plateau ◽  
Large Scale ◽  
Diabatic Heating ◽  
Middle Atmosphere ◽  
Atmospheric Environment ◽  
Monsoon Circulation ◽  
The Tibetan Plateau ◽  
Shallow Convection ◽  
Sensitivity Experiment ◽  
Stratiform Clouds

Cumulus (Cu) from shallow convection is one of the dominant cloud types over the Tibetan Plateau (TP) in the summer according to CloudSat– CALIPSO observations. Its thermodynamic effects on the atmospheric environment and impacts on the large-scale atmospheric circulation are studied in this paper using the Community Atmospheric Model, version 5.3 (CAM5.3). It is found that the model can reasonably simulate the unique distribution of diabatic heating and Cu over the TP. Shallow convection provides the dominant diabatic heating and drying to the lower and middle atmosphere over the TP. A sensitivity experiment indicates that without Cu over the TP, large-scale condensation and stratiform clouds would increase dramatically, which induces enhanced low-level wind and moisture convergence toward the TP, resulting in significantly enhanced monsoon circulation with remote impact on the areas far beyond the TP. Cu therefore acts as a safety valve to modulate the atmospheric environment that prevents the formation of superclusters of stratiform clouds and precipitation over the TP.

scholarly journals Spatio-Temporal Variations of Water Vapor Budget over the Tibetan Plateau in Summer and Its Relationship with the Indo-Pacific Warm Pool

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 828
Author(s):  
Deli Meng ◽  
Qing Dong ◽  
Fanping Kong ◽  
Zi Yin ◽  
Yanyan Li ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tibetan Plateau ◽  
River Basin ◽  
Large Scale ◽  
Warm Pool ◽  
The Tibetan Plateau ◽  
Southern Boundary ◽  
Pacific Warm Pool ◽  
Water Vapor Budget

The water vapor budget (WVB) over the Tibetan Plateau (TP) is closely related to the large-scale atmospheric moisture transportation of the surrounding mainland and oceans, especially for the Indo-Pacific warm pool (IPWP). However, the procession linkage between the WVBs over the TP and its inner basins and IPWP has not been sufficiently elucidated. In this study, the relationship between the summer WVB over the TP and the IPWP was quantitatively investigated using reanalysis datasets and satellite-observed sea surface temperature (SST). The results show that: (1) the mean total summer vapor budget (WVBt) over the TP in the period of 1979–2018 was 72.5 × 106 kg s−1. Additionally, for the 13 basins within the TP, the summer WVB has decreased from southeast to northwest; the Yarlung Zangbo River Basin had the highest WVB (33.7%), followed by the Upper Yangtze River Basin, Ganges River Basin and Qiangtang Plateau. (2) For the past several decades, the WVBt over the TP has experienced an increasing trend (3.81 × 106 kg s−1 decade−1), although the southern boundary budget (WVBs) contributed the most and is most closely related with the WVBt, while the eastern boundary budget (WVBe) experienced a decreasing trend (4.21 × 106 kg s−1 decade−1) which was almost equal to the interdecadal variations of the WVBt. (3) For the IPWP, we defined a new warm pool index of surface latent heat flux (WPI-slhf), and found that an increasing WPI-slhf would cause an anticyclone anomaly in the equatorial western Indian Ocean (near 70° E), resulting in the increased advent of water vapor to the TP. (4) On the interdecadal scale, the correlation coefficients of the variation of the summer WVBt over the TP with the WPI-slhf and Indian Ocean Dipole (IOD) signal were 0.86 and 0.85, respectively (significant at the 0.05% level). Therefore, the warming and the increasing slhf of the IPWP would significantly contribute to the increasing WVB of the TP in recent decades.

Changes in cloud amount over the Tibetan Plateau and impacts of large-scale circulation

2021 ◽  
Vol 249 ◽  
pp. 105332
Author(s):  
Qianrong Ma ◽  
Qinglong You ◽  
Yujun Ma ◽  
Yu Cao ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Large Scale ◽  
Cloud Amount ◽  
The Tibetan Plateau ◽  
Large Scale Circulation

scholarly journals Effects of Liquid Phase Cloud Microphysical Processes in Mixed Phase Cumulus Clouds over the Tibetan Plateau

2019 ◽  
Author(s):  
Xiaoqi Xu ◽  
Chunsong Lu ◽  
Yangang Liu ◽  
Wenhua Gao ◽  
Yuan Wang ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Tibetan Plateau ◽  
Large Scale ◽  
Precipitation Event ◽  
The Tibetan Plateau ◽  
Phase Precipitation ◽  
Physical Reason ◽  
Surface Precipitation ◽  
Skill Scores ◽  
Microphysical Processes

Abstract. Overprediction of precipitation over the Tibetan Plateau is often found in numerical simulations, which is thought to be related to coarse grid sizes or inaccurate large-scale forcing. In addition to confirming the important role of model grid sizes, this study shows that liquid-phase precipitation parameterization is another key culprit, and underlying physical mechanisms are revealed. A typical summer plateau precipitation event is simulated with the Weather Research and Forecasting (WRF) model by introducing different parameterizations of liquid-phase microphysical processes into the commonly used Morrison scheme, including autoconversion, accretion, and entrainment-mixing mechanisms. All simulations can reproduce the general spatial distribution and temporal variation of precipitation. The precipitation in the high-resolution domain is less overpredicted than in the low-resolution domain. The accretion process plays more important roles than other liquid-phase processes in simulating precipitation. Employing the accretion parameterization considering raindrop size makes the total surface precipitation closest to the observation which is supported by the Heidke skill scores. The physical reason is that this accretion parameterization can suppress fake accretion and liquid-phase precipitation when cloud droplets are too small to initiate precipitation.

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