The Tibetan Plateau (TP) is known for its influence on the weather and climate of Asia (e.g., Boos & Kuang, 2010; G. X. Wu et al. 2012; and references cited therein). Previous studies have focused on the dynamic and thermal effects of the Himalayas and the main body of the TP. For example, Yeh et al. (1957) found that the TP provides about 2 K day −1 sensible heat to warm the troposphere across its surface in boreal summer. Yanai et al. (1992) and C. P. Li and Yanai (1996) suggested that the supply of sensible heat from the TP surface in spring results in the reversal of the land-sea temperature contrast and drives the vertical monsoon circulation. Wu et al. (1997) proposed the sensible heat pump effect of the TP, and Wu et al. (2007, 2012) further addressed the impact of the TP thermal condition on the Asian summer monsoon. According to the theories of convective quasiequilibrium (Boos & Emanuel, 2009; Emanuel et al. 1994; Molnar & Emanuel, 1999), Boos and Kuang (2010) found that the mountains south and west of the TP produce strong South Asian monsoon by insulating the thermal maximum over India from the extratropics. Rajagopalan and Molnar (2013) suggested that the TP thermal condition, as represented by the moist static energy of the atmosphere, is correlated with monsoonal rainfall in the early and late monsoon season. Note that above-mentioned studies are associated with the climate effects of the Himalayas or the main part of the TP. However, there are few studies on the southeastern edge of the TP (SEETP). The SEETP is characterized by distinctive terrain, where the east-west oriented Himalayas merge with the north-south oriented Hengduan Mountains (Figures 1a and 1b; Onogi et al., 2007; Kobayashi et al., 2015). The south-north oriented mountains have a barrier function on the prevailing southwesterly winds during the whole year, and those deep valleys play as corridors which let water vapor transport from Indian Ocean to high-latitude areas (Pan et al. 2012). As a result of this particular topographical pattern, the early spring flood over the SEETP generally starts in February during the peach blossom season (red and blue bars in Figure 1c; D.
This study investigates the impact of the Indian and East Asian summer monsoons on the diurnal temperature range (DTR) in the low-latitude highlands of China (CLLH) based on in-situ DTR observations, ERA5 reanalysis data, and numerical simulations. Diagnoses indicate that the DTR in the CLLH shows a significant positive correlation with the Indian summer monsoon (ISM), while a negative correlation with the East Asian summer monsoon (EASM). When a strengthened ISM occurs with a weakened EASM, an anomalous anticyclonic circulation with downward motion is excited over the CLLH. This anomalous circulation pattern increases the DTR in the rainy season by reducing the medium and high cloud cover in the CLLH. When a weakened ISM with a strengthened EASM decreases the DTR over the CLLH in the rainy season. Numerical experiments help to verify this crucial physical process linking the variability of the ISM and EASM with the DTR in the CLLH. The model results further indicate that the covariability of ISM and EASM contributes most to the variability of the rainy season DTR in the CLLH, followed by the individual variability of the EASM, and the smallest contribution to the rainy season DTR in the CLLH is the individual variability of the ISM.
This study explores the linkage of the circumglobal teleconnection (CGT) on the variability of early spring diabatic heating over the Southeast Asian low-latitude highlands (SEALLH) using ERA5 data. The early spring diabatic heating over the SEALLH shows significant interannual variability with a quasi-3-yr period. Anomalies in the advection of the early spring diabatic heating in the troposphere over the SEALLH associated with CGT are mainly responsible for the interannual variability of early spring diabatic heating over the SEALLH. When CGT is in phase with an anomalous cyclone over the eastern midlatitude North Atlantic, an anomalous cyclone usually dominates the west SEALLH throughout the troposphere. Stronger-than-normal southerly winds located on the east flank of the anomalous cyclone in the lower–upper troposphere transport more high-enthalpy air mass from lower latitudes to the SEALLH and then result in stronger-than-normal early spring diabatic heating over the SEALLH. When CGT is in phase with an anomalous anticyclone over the eastern North Atlantic, the opposite conditions occur, and weaker-than-normal early spring diabatic heating is observed over the SEALLH. Such significant correlation between CGT and early spring diabatic heating over the SEALLH can persist from winter to early summer. The key physical processes revealed in the observational analysis are mostly confirmed by the historical simulation performed with the EC-EARTH3 model. Significance Statement The low-latitude highlands in Southeast Asia are one of the earliest diabatic heating sources in the Asian summer monsoon region. Variability of diabatic heating over the low-latitude highlands in Southeast Asia significantly regulates the weather and climate over the Asian summer monsoon region. However, the interannual variability of early spring diabatic heating over the low-latitude highlands in Southeast Asia remains unclear. This study determines that the circumglobal teleconnection links with the interannual variability of early spring diabatic heating over the low-latitude highlands in Southeast Asia via modulating the local advection process from the previous winter. These results build a bridge connecting the anomalous signals occurring in the upper reaches of the low-latitude highlands in Southeast Asia with the weather and climate in the local and lower reaches of the low-latitude highlands in Southeast Asia.
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