Intraseasonal soil moisture-atmosphere feedbacks on the Tibetan Plateau circulation

AbstractSubstantial intraseasonal precipitation variability is observed across the Tibetan Plateau (TP) during boreal summer associated with the subtropical jet location and the Silk Road pattern. Weather station data and satellite observations highlight a sensitivity of soil moisture and surface fluxes to this variability. During rain-free periods of two or more days, skin temperatures are shown to rise as the surface dries, signalling decreased evaporative fraction. Surface fluxes are further enhanced by relatively clear skies. In this study we use an atmospheric reanalysis to assess how this surface flux response across the TP influences local and remote conditions.Increased surface sensible heat flux induced by decreased soil moisture during a regional dry event leads to a deepening of the planetary boundary-layer and the development of a heat low. Consistent with previous studies, heat low characteristics exhibit pronounced diurnal variability driven by anomalous daytime surface warming. For example, low-level horizontal winds are weakest during the afternoon and intensify overnight when boundary-layer turbulence is minimal. The heat low favours an upper-tropospheric anticyclone which induces an upper-level Rossby wave and leads to negative upperlevel temperature anomalies across southern China. The Rossby wave intensifies the upper-level cyclonic circulation across central China, whilst upperlevel negative temperature anomalies across south China extends the west Pacific subtropical high westward. These circulation anomalies influence temperature and precipitation anomalies across much of China. The association between land-atmosphere interactions across the TP, large-scale atmospheric circulation characteristics, and precipitation in east Asia highlights the importance of intraseasonal soil moisture dynamics on the TP.

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A numerical process study on the rapid transport of stratospheric air down to the surface over western North America and the Tibetan Plateau

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-6535-2019 ◽

2019 ◽

Vol 19 (9) ◽

pp. 6535-6549 ◽

Cited By ~ 2

Author(s):

Bojan Škerlak ◽

Stephan Pfahl ◽

Michael Sprenger ◽

Heini Wernli

Keyword(s):

Boundary Layer ◽

Tibetan Plateau ◽

Surface Ozone ◽

Vertical Transport ◽

The Tibetan Plateau ◽

Near Surface ◽

Air Mass ◽

Ozone Concentrations ◽

Rapid Transport ◽

Upper Level

Abstract. Upper-level fronts are often associated with the rapid transport of stratospheric air along tilted isentropes to the middle or lower troposphere, where this air leads to significantly enhanced ozone concentrations. These plumes of originally stratospheric air can only occasionally be observed at the surface because (i) stable boundary layers prevent an efficient vertical transport down to the surface, and (ii) even if boundary layer turbulence were strong enough to enable this transport, the originally stratospheric air mass can be diluted by mixing, such that only a weak stratospheric signal can be recorded at the surface. Most documented examples of stratospheric air reaching the surface occurred in mountainous regions. This study investigates two such events, using a passive stratospheric air mass tracer in a mesoscale model to explore the processes that enable the transport down to the surface. The events occurred in early May 2006 in the Rocky Mountains and in mid-June 2006 on the Tibetan Plateau. In both cases, a tropopause fold associated with an upper-level front enabled stratospheric air to enter the troposphere. In our model simulation of the North American case, the strong frontal zone reaches down to 700 hPa and leads to a fairly direct vertical transport of the stratospheric tracer along the tilted isentropes to the surface. In the Tibetan Plateau case, however, no near-surface front exists and a reservoir of high stratospheric tracer concentrations initially forms at 300–400 hPa, without further isentropic descent. However, entrainment at the top of the very deep boundary layer (reaching to 300 hPa over the Tibetan Plateau) and turbulence within the boundary layer allows for downward transport of stratospheric air to the surface. Despite the strongly differing dynamical processes, stratospheric tracer concentrations at the surface reach peak values of 10 %–20 % of the imposed stratospheric value in both cases, corroborating the potential of deep stratosphere-to-troposphere transport events to significantly influence surface ozone concentrations in these regions.

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Simulation Analysis of Local Land Atmosphere Coupling in Rainy Season over a Typical Underlying Surface in the Tibetan Plateau

10.5194/hess-2020-199 ◽

2020 ◽

Author(s):

Genhou Sun ◽

Zeyong Hu ◽

Yaoming Ma ◽

Zhipeng Xie ◽

Jiemin Wang ◽

...

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

Rainy Season ◽

Surface Fluxes ◽

Underlying Surface ◽

The Tibetan Plateau ◽

Spatial Distributions ◽

Initial Soil Moisture ◽

Initial Soil ◽

The Relationship

Abstract. The Local land atmosphere coupling (LoCo) focuses on the interactions between soil conditions, surface fluxes, planetary boundary layer (PBL) growth, and the formations of convective clouds and precipitations. Study of LoCo over the Tibetan Plateau (TP) is of great significance for understanding TP's role in the Asian Water Tower. A series of real-case simulations using the Weather Research and Forecasting Model (WRF) with different combinations of land surface models (LSM) schemes and PBL schemes has been carried out to investigate the LoCo characteristics over a typical underlying surface in the central TP in rainy season. The LoCo characteristics in the study area are analyzed by applying a mixing diagram to the simulation results. The analysis indicates that the WRF simulations using the Noah with BouLac, MYNN, and YSU produce closer results to the observation in terms of curves of Cp*θ and Lv*q, surface fluxes (Hsfc and LEsfc), entrainment fluxes (Hent and LEent) at site BJ/Nagqu than those using the CLM with BouLac, MYNN, and YSU. The frequency distributions of Hsfc, LEsfc, Hent, and LEent in the study area confirm this result. The spatial distributions of simulated Hsfc, LEsfc, Hent, and LEent using WRF with Noah and BouLac suggest that the spatial distributions of Hsfc and LEsfc in the study area are consistent with that of soil moisture, but the spatial distributions of Hent and LEent are quite different from that of soil moisture. A close examination of the relationship between entrainment fluxes and cloud water content (QCloud) reveals that the grids with small Hent and large LEent tend to have high QCloud and Hsfc, suggesting that high Hsfc is conductive to convective cloud formation, which leads to small Hent and large LEent. Sensitivity analysis of LoCo to the soil moisture at site BJ/Nagqu indicates that on a sunny day, an increase in soil moisture leads to an increase in LEsfc but decreases in Hsfc, Hent, and LEent. The sensitivity of the relationship between simulated maximum daytime PBL height (PBLH) and mean daytime evapotranspiration (EF) in the study area to soil moisture indicates that the rate at which the maximum daytime PBLH decreases with the mean EF increase as the initial soil moisture goes up. The analysis of simulated Hsfc, LEsfc, Hent, and LEent under different soil moisture conditions reveals that the frequency of Hent ranging from 80 to 240 W/m2 and the frequency of LEent ranging from −240 to −90 W/m2 both increase as the initial soil moisture increases. Coupled with the changes in QCloud, the changes in Hent and LEent as the initial soil moisture increases indicate that the rise in soil moisture leads to an increase in the cloud amount but a decrease in QCloud.

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Using a WRF simulation to examine regions where convection impacts the Asian summer monsoon anticyclone

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-24809-2013 ◽

2013 ◽

Vol 13 (9) ◽

pp. 24809-24853

Author(s):

N. K. Heath ◽

H. E. Fuelberg

Keyword(s):

Boundary Layer ◽

Water Vapor ◽

Tibetan Plateau ◽

Summer Monsoon ◽

Asian Summer Monsoon ◽

Satellite Observations ◽

The Tibetan Plateau ◽

Asian Summer ◽

Upper Level

Abstract. The Asian summer monsoon is a prominent feature of the global circulation that is associated with an upper-level anticyclone (ULAC) that stands out vividly in satellite observations of trace gases. The ULAC also is an important region of troposphere-to-stratosphere transport. We ran the Weather Research and Forecasting (WRF) model at convective-permitting scales (4 km grid spacing) between 10–20 August 2012 to understand the role of convection in transporting boundary layer air into the upper-level anticyclone. Such high-resolution modeling of the Asian ULAC previously has not been documented in the literature. Comparison of our WRF simulation with reanalysis and satellite observations showed that WRF simulated the atmosphere sufficiently well to be used to study convective transport into the ULAC. A back-trajectory analysis based on hourly WRF output showed that > 90% of convectively influenced parcels reaching the ULAC came from the Tibetan Plateau (TP) and the southern slope (SS) of the Himalayas. A distinct diurnal cycle is seen in the convective trajectories, with their greatest impact occurring between 1600–2300 local solar time. This finding highlights the role of "everyday" diurnal convection in transporting boundary layer air into the ULAC. WRF output at 15 min intervals was produced for 16 August to examine the convection in greater detail. This high-temporal output revealed that the weakest convection in the study area occurred over the TP. However, because the TP is at 3000–5000 m a.m.s.l., its convection does not have to be as strong to reach the ULAC as in lower altitude regions. In addition, because the TP's elevated heat source is a major cause of the ULAC, we propose that convection over the TP and the neighboring SS is ideally situated geographically to impact the ULAC. The vertical mass flux of water vapor into the ULAC also was calculated. Results show that the TP and SS regions dominate other Asian regions in transporting moisture vertically into the ULAC. Because convection reaching the ULAC is more widespread over the TP than nearby, we propose that the abundant convection partially explains the TP's dominant water vapor fluxes. In addition, greater outgoing longwave radiation reaches the upper levels of the TP due to its elevated terrain. This creates a warmer ambient upper level environment, allowing parcels with greater saturation mixing ratios to enter the ULAC. Lakes in the Tibetan Plateau are shown to provide favorable conditions for deep convection during the night.

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Impact of soil moisture on afternoon convection triggering over the Tibetan Plateau based on 1‐D boundary layer model

Journal of Geophysical Research Atmospheres ◽

10.1029/2021jd035591 ◽

2022 ◽

Author(s):

Cailing Zhao ◽

Xianhong Meng ◽

Yueqing Li ◽

Shihua Lyu ◽

Jianping Guo ◽

...

Keyword(s):

Boundary Layer ◽

Soil Moisture ◽

Tibetan Plateau ◽

The Tibetan Plateau ◽

Layer Model ◽

Boundary Layer Model

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Reasons for the Extremely High-Ranging Planetary Boundary Layer over the Western Tibetan Plateau in Winter

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0148.1 ◽

2016 ◽

Vol 73 (5) ◽

pp. 2021-2038 ◽

Cited By ~ 17

Author(s):

Xuelong Chen ◽

Bojan Škerlak ◽

Mathias W. Rotach ◽

Juan A. Añel ◽

Zhonbgo Su ◽

...

Keyword(s):

Boundary Layer ◽

Tibetan Plateau ◽

Sea Level ◽

Planetary Boundary Layer ◽

Weather Prediction ◽

Atmospheric Stability ◽

Small Scale ◽

The Tibetan Plateau ◽

Single Column ◽

Upper Level

Abstract The planetary boundary layer (PBL) over the Tibetan Plateau (with a mean elevation about 4 km above sea level) reaches an unmatched height of 9515 m above sea level. The proximity of this height to the tropopause facilitates an exchange between the stratosphere and the boundary layer. However, the underlying mechanisms responsible for this unique PBL have remained uncertain. Here, the authors explore these mechanisms and their relative importance using measurements of the PBL, the associated surface fluxes, and single-column and regional numerical simulations, as well as global reanalysis data. Results indicate that the dry conditions of both ground soil and atmosphere in late winter cannot explain the special PBL alone. Rather, the results from a single-column model demonstrate the key influence of the stability of the free atmosphere upon the growth of extremely deep PBLs over the Tibetan Plateau. Simulations with the numerical weather prediction model Consortium for Small-Scale Modelling (COSMO) exhibit good correspondence with the observed mean PBL structure and realistic turbulent kinetic energy distributions throughout the PBL. Using ERA-Interim, the authors furthermore find that weak atmospheric stability and the resultant deep PBLs are associated with higher upper-level potential vorticity (PV) values, which in turn correspond to a more southerly jet position and higher wind speeds. Upper-level PV structures and jet position thus influence the PBL development over the Tibetan Plateau.

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Interannual Variations and Trends in Remotely Sensed and Modeled Soil Moisture in China

Journal of Hydrometeorology ◽

10.1175/jhm-d-18-0003.1 ◽

2018 ◽

Vol 19 (5) ◽

pp. 831-847 ◽

Cited By ~ 7

Author(s):

Binghao Jia ◽

Jianguo Liu ◽

Zhenghui Xie ◽

Chunxiang Shi

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

Surface Soil ◽

Central China ◽

The Tibetan Plateau ◽

Interannual Variations ◽

Surface Soil Moisture ◽

Community Land Model ◽

In Situ Observations

Abstract In this study, a microwave-based multisatellite merged product released from the European Space Agency’s Climate Change Initiative (ESA CCI) and two model-based simulations from the Community Land Model 4.5 (CLM4.5) and Global Land Data Assimilation System (GLDAS) were used to investigate interannual variations and trends of soil moisture in China between 1979 and 2010. They were also evaluated using in situ observations from the nationwide agrometeorological network. These three datasets show consistent drying trends for surface soil moisture in northeastern and central China, as well the eastern portion of Inner Mongolia, and wetting trends in the Tibetan Plateau, which are also identified by in situ observations. Trends in the root-zone soil moisture are in line with those of surface soil moisture seen in the CLM4.5 and GLDAS simulations obtained from most areas in China (78%–88%), except for northwestern China and southwest of the Tibetan Plateau. Moreover, the drying trend intensifies with increasing soil depth. Taking the in situ measurements as reference, it is found that ESA CCI has better accuracy in identifying the significant drying trends while CLM4.5 and GLDAS capture wetting trends better. Compared to temperature, precipitation is the primary factor responsible for these trends, which controls the direction of soil moisture changes, while increasing temperatures can also enhance soil drying during periods of decreased precipitation.

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Simulation Analysis of Local Land Atmosphere Coupling in Rainy Season over a Typical Underlying Surface in the Tibetan Plateau

10.5194/egusphere-egu2020-6648 ◽

2020 ◽

Author(s):

Genhou Sun ◽

Zeyong Hu ◽

Yaoming Ma ◽

Song Yang

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

Rainy Season ◽

Surface Fluxes ◽

Underlying Surface ◽

The Tibetan Plateau ◽

Spatial Distributions ◽

Initial Soil Moisture ◽

Initial Soil ◽

The Relationship

The Local land atmosphere coupling (LoCo) focuses on the interactions between soil conditions, surface fluxes, PBL growth, and the formations of convective clouds and precipitations, and a study of LoCo over the Tibetan Plateau (TP) is of great significance to understand its role of &#8220;Asian Water Tower&#8221;. This study investigates the LoCo characteristics over a typical underlying surface in central TP in the rainy season based on a series of real case simulations using Weather Research and Forecasting Model (WRF) with different combinations of land surface model (LSM) schemes and planetary boundary layer (PBL) schemes based on in-situ measurements. Then the LoCo characteristics over a typical underlying surface in central TP are analyzed using a mixing diagram. The simulations results indicates that WRF simulations using Noah with BouLac, MYNN, and YSU produce much better results in terms of curves of Cp*theta and Lv*q, surface fluxes (Hsfc and LEsfc), entrainment fluxes (Hent and LEent) at site BJ/Nagqu that those using CLM with BouLac, MYNN, and YSU do. The frequency distributions of Hsfc, LEsfc, Hent, and LEent in the study area confirmed this result. The spatial distributions of simulated Hsfc, LEsfc, Hent, and LEent using WRF with Noah and BouLac suggest that the spatial distributions of Hsfc and LEsfc in the study area show a good consistent with that of soil moisture, but the spatial distributions of Hent and LEent are quite different from that of soil moisture. A close examination of the relationship between entrainment fluxes and cloud water contents (QCloud) reveals that the grids with small Hent and large LEent are likely to have high QCloud and Hsfc. This means that high Hsfc is conductive to convective cloud formations, which lead to small Hent and large LEent. Sensitivity analysis of LoCo to the soil moisture at site BJ/Nagqu indicates that in a sunny day, an increase in soil moisture leads to an increase in LEsfc but a decrease in Hsfc, Hent, and LEent. The sensitivity of the relationship between simulated max daytime PBLH and mean daytime EF in the study area to soil moistures indicates that the rate at which the max daytime PBLH decrease with the mean EF increases as the initial soil moisture goes up. The analysis of simulated Hsfc, LEsfc, Hent, and LEent under different soil moisture conditions reveals that the frequencies of Hent ranging from 80 W/m2 and over 240 W/m2 and frequency of LEent ranging from -240 W/m2 to -90 W/m2 increase as the initial soil moisture increases. Coupled with the changes in QCloud, the changes in Hent and LEent as the initial soil moisture increases indicate that the increase in soil moisture lead to an increase in cloud amounts but a decrease in QCloud.

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

Monthly Weather Review ◽

10.1175/2009mwr2826.1 ◽

2009 ◽

Vol 137 (7) ◽

pp. 2286-2304 ◽

Cited By ~ 36

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.

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Simulation analysis of local land atmosphere coupling in rainy season over a typical underlying surface in the Tibetan Plateau

Hydrology and Earth System Sciences ◽

10.5194/hess-24-5937-2020 ◽

2020 ◽

Vol 24 (12) ◽

pp. 5937-5951

Author(s):

Genhou Sun ◽

Zeyong Hu ◽

Yaoming Ma ◽

Zhipeng Xie ◽

Jiemin Wang ◽

...

Keyword(s):

Soil Moisture ◽

Tibetan Plateau ◽

Rainy Season ◽

Surface Fluxes ◽

Underlying Surface ◽

The Tibetan Plateau ◽

Spatial Distributions ◽

Initial Soil Moisture ◽

Initial Soil ◽

The Relationship

Abstract. The local land–atmosphere coupling (LoCo) investigates the interactions between soil conditions, surface fluxes, planetary boundary layer (PBL) growth, and the formations of convective clouds and precipitation. Studying LoCo over the Tibetan Plateau (TP) is of great significance for understanding the TP's role in the Asian water tower. A series of real-case simulations, using the Weather Research and Forecasting (WRF) model with different combinations of land surface model (LSM) schemes and PBL schemes, has been carried out to investigate the LoCo characteristics over a typical underlying surface in the central TP in the rainy season. The LoCo characteristics in the study area are analyzed by applying a mixing diagram to the simulation results. The analysis indicates that the WRF simulations, using the Noah with BouLac, Mellor-Yamada Nakanishi and Niino Level-2.5 PBL (MYNN), and Yonsei University (YSU) produce closer results to the observation in terms of curves of Cp⋅θ and Lv⋅q, surface fluxes (Hsfc and LEsfc), entrainment fluxes (Hent, and LEent) at site BJ of Nagqu Station (BJ/Nagqu) than those using the Community Land Model (CLM) with BouLac, MYNN, and YSU. The frequency distributions of Hsfc, LEsfc, Hent, and LEent in the study area confirm this result. The spatial distributions of simulated Hsfc, LEsfc, Hent, and LEent, using WRF with Noah and BouLac, suggest that the spatial distributions of Hsfc and LEsfc in the study area are consistent with that of soil moisture, but the spatial distributions of Hent and LEent are quite different from that of soil moisture. A close examination of the relationship between entrainment fluxes and cloud water content (QCloud) reveals that the grids with small Hent and large LEent tend to have high QCloud and Hsfc, suggesting that high Hsfc is conducive to convective cloud formation, which leads to small Hent and large LEent. A sensitivity analysis of LoCo to the soil moisture at site BJ/Nagqu indicates that, on a sunny day, an increase in soil moisture leads to an increase in LEsfc but decreases in Hsfc, Hent, and LEent. The sensitivity of the relationship between simulated maximum daytime PBL height (PBLH) and mean daytime evapotranspiration (ET) in the study area to soil moisture indicates the rate at which the maximum daytime PBLH decreases with the mean ET increase as the initial soil moisture goes up. The analysis of simulated Hsfc, LEsfc, Hent, and LEent under different soil moisture conditions reveals that the frequency of Hent ranging from 80 to 240 W m−2 and the frequency of LEent ranging from −240 to −90 W m−2 both increase as the initial soil moisture increases. Coupled with the changes in QCloud, the changes in Hent and LEent as the initial soil moisture increases indicate that the rise in soil moisture leads to an increase in the cloud amount but a decrease in QCloud.

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Influence of the Anticyclonic Anomaly in the Subtropical Jet over the Western Tibetan Plateau on the Intraseasonal Variability of the Summer Asian Monsoon in Early Summer

Journal of Climate ◽

10.1175/jcli-d-11-00036.1 ◽

2012 ◽

Vol 25 (4) ◽

pp. 1291-1303 ◽

Cited By ~ 24

Author(s):

Takeshi Watanabe ◽

Koji Yamazaki

Keyword(s):

Tibetan Plateau ◽

Rossby Wave ◽

Arabian Sea ◽

Asian Monsoon ◽

Intraseasonal Variability ◽

Anticyclonic Anomaly ◽

Subtropical Jet ◽

Western Tibetan Plateau ◽

Upper Level ◽

Heat Low

Abstract The upper-level troposphere over the western Tibetan Plateau, where the subtropical jet is located in summer, is a region of marked intraseasonal variability in geopotential height (GPH). This study investigates the influence of an anomaly in this region on the summer Asian monsoon. To this end, the GPH index is defined as the daily geopotential height anomaly at 200 hPa over the region based on 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) data. Composites with respect to strongly positive values of the GPH index are analyzed. The results indicate that the temporary anomaly in the subtropical jet influences the monsoon over South Asia, Southeast Asia, and probably also over East Asia, because of two main processes: the eastward propagation of quasi-stationary Rossby wave anomalies at upper and lower levels along the subtropical jet, and a belt of strong westerlies at 15°N (Arabian Sea–Bay of Bengal–the Philippines). The two mechanisms that underlie the lower-level Rossby wave anomaly are discussed here for the first time, based on the Rossby ray-path theory, as follows: 1) anomalous descent generated by the upper-level anticyclonic anomaly over Afghanistan and the western Tibetan Plateau causes the development of a heat low over the Thar Desert and neighboring areas, and 2) an anomalous southwesterly appears over the Arabian Sea, accompanied by the heat low, and interacts with the Western Ghats, resulting in an anticyclonic anomaly over the Indian subcontinent. The anomaly then starts to propagate eastward along a Rossby waveguide.

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