Observed Linkage between Tibetan Plateau Soil Moisture and South Asian Summer Precipitation and the Possible Mechanism

2021 ◽  
Vol 34 (1) ◽  
pp. 361-377
Author(s):  
Waheed Ullah ◽  
Wang Guojie ◽  
Zhiqiu Gao ◽  
Daniel Fiifi Tawia Hagan ◽  
Asher Samuel Bhatti ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Linear Method ◽  
Summer Precipitation ◽  
Moisture Flux ◽  
Thermal Processes ◽  
The Tibetan Plateau ◽  
Climate Data ◽  
Thermal Profile ◽  
Near Surface

AbstractUnderstanding the Tibetan Plateau (TP) thermal processes is of utmost significance in changing climate. This study investigates the effect of soil moisture in changing the TP thermal profile and consequently summer precipitation in South Asia (SA). Soil moisture from Special Sensor Microwave Imager (SSM/I) developed from the F-08, F-11, and F-13 fundamental climate data record and atmospheric reanalysis from ERA-Interim, MERRA-2, and NCEP/CFSR during 1988–2008 are used. A generalized linear method that assesses the reciprocal forcing between two connected fields, named the coupled manifold technique (CMT), is applied to TP soil moisture and SA summer precipitation. It is revealed that interannual variations of SA precipitation are significantly (confidence level = 99%) impacted by TP soil moisture and the explained ratio of variance in SA is 0.3–0.4. Composite analysis indicates that SA summer precipitation has positive anomalies in response to dry TP soil moisture in the previous spring and vice versa. For understanding the possible mechanism, thermal processes, relative humidity, wind components, and moisture flux anomalies were calculated for dry and wet TP soil moisture and summer precipitation. The results suggested that TP soil moisture is likely to regulate near-surface energy balance and diabatic heating profile over TP. As a result, the surrounding lower-level westerlies (easterlies) (at 850 hPa) converge (diverge), associated with divergence (convergence) at the upper troposphere (200 hPa). The westerlies (easterlies) are usually moisture-rich (moisture-deficient) and thus cause more (less) precipitation in western (eastern) SA. It is thus suggested that the spring soil moisture may affect the thermal profile of TP, affecting the summer precipitation in SA as a consequence.

scholarly journals Long term soil moisture mapping over the Tibetan plateau using Special Sensor Microwave/Imager

2014 ◽  
Vol 18 (4) ◽  
pp. 1323-1337 ◽  
Author(s):  
R. van der Velde ◽  
M. S. Salama ◽  
T. Pellarin ◽  
M. Ofwono ◽  
Y. Ma ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Mean Squared Error ◽  
Potential Evapotranspiration ◽  
Warm Season ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
The Tibetan Plateau ◽  
Near Surface

Abstract. This paper discusses soil moisture retrievals over the Tibetan Plateau from brightness temperature (TB's) observed by the Special Sensor Microwave Imagers (SSM/I's) during the warm seasons of the period from July 1987 to December 2008. The Fundamental Climate Data Record (FCDR) of F08, F11 and F13 SSM/I satellites by the Precipitation Research Group of Colorado State University is used for this study. A soil moisture retrieval algorithm is developed based on a radiative transfer model that simulates top-of-atmosphere TB's whereby effects of atmosphere are calculated from near-surface forcings obtained from a bias-corrected dataset. Validation of SSM/I retrievals against in situ measurements for a two-and-half year period (225 matchups) gives a Root Mean Squared Error of 0.046 m3 m−3. The agreement between retrievals and Noah simulations from the Global Land Data Assimilation System is investigated to further provide confidence in the reliability of SSM/I retrievals at the Plateau-scale. Normalised soil moisture anomalies (N) are computed on a warm seasonal (May–October) and on a monthly basis to analyse the trends present within the products available from July 1987 to December 2008. The slope of linear regression functions between N and time is used to quantify the trends. Both the warm season and monthly N indicate severe wettings of 0.8 to almost 1.6 decade−1 in the centre of the Plateau. Correlations are found by the trend with elevation for the warm season as a whole and the individual months May, September and October. The observed wetting of the Tibetan Plateau agrees with recent findings on permafrost retreat, precipitation increase and potential evapotranspiration decline.

scholarly journals Long term soil moisture mapping over the Tibetan Plateau using Special Sensor Microwave/Imager

2013 ◽  
Vol 10 (5) ◽  
pp. 6629-6667 ◽  
Author(s):  
R. van der Velde ◽  
M. S. Salama ◽  
T. Pellarin ◽  
M. Ofwono ◽  
Y. Ma ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Mean Squared Error ◽  
Potential Evapotranspiration ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
The Tibetan Plateau ◽  
Data Set ◽  
Near Surface

Abstract. This paper discusses soil moisture retrievals over the Tibetan Plateau from brightness temperature (TB's) observed by the Special Sensor Microwave Imagers (SSM/I's) during warm seasons of the period from July 1987 to December 2008. The Fundamental Climate Data Record (FCDR) of F08, F11 and F13 SSM/I satellites by the Precipitation Research Group of Colorado State University is used for this study. A soil moisture retrieval algorithm is developed based on a radiative transfer model that simulates top-of-atmosphere TB's whereby effects of atmosphere are calculated from near-surface forcings obtained from a bias-corrected data set. Validation of SSM/I retrievals against in situ measurements for a two-and-half year period (225 matchups) gives a Root Mean Squared Error of 0.046 m3 m−3. The agreement between retrievals and Noah simulations from the Global Land Data Assimilation System (GLDAS) is investigated to further provide confidence in the reliability of SSM/I retrievals at the plateau-scale. Normalized soil moisture anomalies (N) are computed on an annual and monthly basis to analyze the trends present within the products available for July 1987 to December 2008. The slope of linear regression functions between N and time is used to quantify the trends. Both the annual and monthly N indicate severe wettings of 0.8 to almost 1.6 decade−1 in the center of the plateau. Correlations are found of the trend with elevation on an annual basis and for the months May, September and October. The observed wetting of the Tibetan Plateau agrees with recent findings of permafrost retreat, precipitation increase and potential evapotranspiration decline.

scholarly journals Atmospheric Thermal and Dynamic Vertical Structures of Summer Hourly Precipitation in Jiulong of the Tibetan Plateau

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 505
Author(s):  
Yonglan Tang ◽  
Guirong Xu ◽  
Rong Wan ◽  
Xiaofang Wang ◽  
Junchao Wang ◽  
...  
Keyword(s):  
Wind Speed ◽  
Tibetan Plateau ◽  
Precipitation Amount ◽  
Summer Precipitation ◽  
The Tibetan Plateau ◽  
Hourly Precipitation ◽  
Air Convection ◽  
Precipitation Variation ◽  
Long Term Observation

It is an important to study atmospheric thermal and dynamic vertical structures over the Tibetan Plateau (TP) and their impact on precipitation by using long-term observation at representative stations. This study exhibits the observational facts of summer precipitation variation on subdiurnal scale and its atmospheric thermal and dynamic vertical structures over the TP with hourly precipitation and intensive soundings in Jiulong during 2013–2020. It is found that precipitation amount and frequency are low in the daytime and high in the nighttime, and hourly precipitation greater than 1 mm mostly occurs at nighttime. Weak precipitation during the daytime may be caused by air advection, and strong precipitation at nighttime may be closely related with air convection. Both humidity and wind speed profiles show obvious fluctuation when precipitation occurs, and the greater the precipitation intensity, the larger the fluctuation. Moreover, the fluctuation of wind speed is small in the morning, large at noon and largest at night, presenting a similar diurnal cycle to that of convective activity over the TP, which is conductive to nighttime precipitation. Additionally, the inverse layer is accompanied by the inverse humidity layer, and wind speed presents multi-peaks distribution in its vertical structure. Both of these are closely related with the underlying surface and topography of Jiulong. More studies on physical mechanism and numerical simulation are necessary for better understanding the atmospheric phenomenon over the TP.

scholarly journals Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments

2014 ◽  
Vol 10 (1) ◽  
pp. 91-106 ◽  
Author(s):  
E. Dietze ◽  
F. Maussion ◽  
M. Ahlborn ◽  
B. Diekmann ◽  
K. Hartmann ◽  
...  
Keyword(s):  
Grain Size ◽  
Sediment Transport ◽  
Tibetan Plateau ◽  
Transport Processes ◽  
The Tibetan Plateau ◽  
Dust Deposition ◽  
Northerly Wind ◽  
Near Surface ◽  
Depositional Processes ◽  
End Members

Abstract. Grain-size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy, this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain-size end-member modelling analysis. Between three and five robust grain-size end-member subpopulations were distinguished at different sites from similarly–likely end-member model runs. Their main modes were grouped and linked to common sediment transport and depositional processes that can be associated with contemporary Tibetan climate (precipitation patterns and lake ice phenology, gridded wind and shear stress data from the High Asia Reanalysis) and local catchment configurations. The coarse sands and clays with grain-size modes >250 μm and <2 μm were probably transported by fluvial processes. Aeolian sands (~200 μm) and coarse local dust (~60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~25 μm may derive from near-by sources that keep in longer term suspension. The continuous background dust is differentiated into two robust end members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain-size end members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.

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