Association between regional summer monsoon onset in South Asia and Tibetan Plateau thermal forcing

Abstract

By using multiple data sources and numerical simulation results from the atmospheric general circulation model (AGCM) of CAM4.0 (Community Atmosphere Model, version 4), we investigated the effect of thermal forcing over the Tibetan Plateau (TP) on the onset of the summer monsoon in the Arabian Sea (AS) and India. Results indicate that the spatial distribution of diabatic heating over the TP in May is a southeastern–northwestern inverse pattern. This diabatic heating shows a robust negative relationship with the onset date of the summer monsoon over the AS and India. A positive diabatic heating seesaw pattern can enhance the ascending (descending) motion over the southeastern (northwestern) TP, corresponding to above (below) normal in- situ precipitation. Temperature budget diagnosis reveals that the adiabatic heating due to anomalous vertical motion and relevant horizontal advection of temperature in the mid-upper troposphere are responsible for the warming over the TP. Consequently, the reversal of the meridional temperature gradient from winter to summer over South Asian regions occurs earlier than the climate-mean state. Furthermore, the diabatic heating over the TP induces an enhanced and westward-extended South Asian High (SAH), which together with the easterly along the southern flank of the SAH superimpose on the low-level westerly flow over the AS and India, results in intensive upper-level divergence-pumping and upward motion. This anomalous circulation configuration in lower and upper levels further facilitates an earlier onset of the summer monsoon in AS and India. These findings are corroborated in the sensitivity runs based on CAM4.0.

Diagnosing Potential Impacts of Tibetan Plateau Spring Soil Moisture Anomalies on Summer Precipitation and Floods in the Yangtze River Basin

“…Because there is no diabatic heating at different pressure levels in ERA5, we used MERRA‐2 diabatic heating at a resolution of 0.625° × 0.5° ranging from 1000 to 200 hPa (Gelaro et al., 2017). The used MERRA‐2 diabatic heating over the TP has also been compared with the Japanese 55‐yr Reanalysis (JRA‐55) data (D. Hu et al., 2022; Kobayashi et al., 2015), and they show significantly high consistency in terms of interannual variations (Figure S2 in the Supporting Information ). An improved topography is used in the MERRA‐2 model and can better capture the topography variations at different pressure levels over the TP (figures not shown).…”

Comparative Analysis of Summer Atmospheric Heat Sources Over the Qinghai-Xizang Plateau from Different Reanalysis Data and Radiosonde Data

“…The dynamic and thermodynamic effects of the Qinghai-Tibet Plateau (QTP) on regional and global weather and climate have been widely recognized (Wu et al 2007;Wu et al 1997;Duan et al 2013;He et al 2015). Numerous studies have shown that the strength of atmospheric heat source over the QTP not only affects the strength of the East Asian Summer Monsoon, but also plays an important role in its outbreak, evolution, and promotion (Wu et al 2015;Xiao et al 2016;Wang et al 2017;Hu et al 2022;Yu et al 2023). The QTP is also important in the strength and spatial pattern of summer precipitation in eastern China through its thermodynamic effect (Xu et al 2013;Lai and Gong 2017;Shi et al 2019;Huang et al 2020).…”

Diverse Interannual Variability of Asian Summer Monsoon Onset Process

“…Together, they induce the monsoon onset over India by extending the South Asian High westward (B. Liu et al., 2013; Wu & Liu, 2014; Y. Zhang et al., 2014). At the interannual timescale, some studies have proposed a positive correlation of the BOB monsoon onset time with those of the SCS and India after the 1980s (Hu et al., 2022; Tamura & Koike, 2010; Zeng et al., 2021). However, since the criteria employed for ASM onset differ across studies, the interannual relationship between each stage of ASMOP remains uncertain.…”

“…However, since the criteria employed for ASM onset differ across studies, the interannual relationship between each stage of ASMOP remains uncertain. Furthermore, the interannual variability of the dates of ASM onset relies on the ENSO‐related sea surface temperature anomalies (SSTAs) (Ju & Slingo, 1995; X. Wang et al., 2013; Webster & Yang, 1992), thermal forcing of the Tibetan Plateau (Hu et al., 2022; Li & Yanai, 1996; B. Liu & Zhu, 2021), and land surface temperature over the Eurasian continent (Choudhury et al., 2019; Zhu & Li, 2017). However, it remains unclear as to how these factors, especially the extra‐equatorial SSTAs, affect the interannual changes in the stepwise ASMOP.…”

“…• The Asian summer monsoon onset process (ASMOP) shows distinct interannual modes in the tropics • El Niño-Southern Oscillation determines the interannual variability in ASMOP over India, the Bay of Bengal, and the southern South China Sea (SCS) • The southwestern Indian and western Pacific sea surface temperature anomalies modulate ASMOP over India and the northern SCS via air-sea interaction, respectively thermal forcing of the Tibetan Plateau (Hu et al, 2022;Li & Yanai, 1996;, and land surface temperature over the Eurasian continent (Choudhury et al, 2019;Zhu & Li, 2017). However, it remains unclear as to how these factors, especially the extra-equatorial SSTAs, affect the interannual changes in the stepwise ASMOP.…”