Numerical simulation of Tibetan Plateau heating anomalyinfluence on westerly jet in spring

The intensity and location of the westerly jet (WJ) in the mid-latitudes of the Northern Hemisphere has been closely related to weather and climate changes in Eurasia. In this paper, we analyzed the seasonal and inter-annual variations in the strength and position of the WJ, using the NCEP-DOE reanalysis II (NCEP) data. Spring is the period that the Tibetan Plateau (TP) transits from a cold to a warm condition, and at the same time the WJ weakens and moves northward. Correlation analysis showed that the westerly wind over the north (south) of the TP has a significant positive (negative) correlation with the TP surface temperature in spring during 1979–2013 (99.9% significance level). In spring, surface sensible heat release dominates thermal conditions of the TP, while the contribution of latent heat becomes important in summer. We conducted three numerical experiments to determine the effects of the TP surface sensible heat flux anomaly in spring on the intensity and location of the WJ using the community atmosphere model 5 (CAM5). Experimental results indicated that changing the TP surface sensible heat flux can produce changes in the TP heat sources. When the TP sensible heat flux is switched off (TPSHL), the TP surface has a lower temperature and no longer heats up the middle and upper troposphere, and leads to a maximum cooling of –1.2◦C at 200 hPa over the TP with a significance level of 95%. In spring, the abnormal low temperature over the TP caused the WJ to strengthen and move southward compared with the control experiment (CTL), and this results in a westerly (easterly) wind anomaly over the south (north) of the TP with a significance level of 95%. We obtained the opposite conclusion from the comparison of the enhanced TP surface sensible heat flux (TPSHH) with CTL test results. In TPSHL, the WJ is still steadily located near 30◦N in May as well as April, i.e., the first northward jump occurs from May to June which is a delay of one month compared to CTL. While in TPSHH, the WJ moves northward approximately 10◦ of latitude from April to May which is 5◦ larger than CTL. Thus, the strength and north–south migration of WJ is closely linked to the TP heat source, especially during the spring–summer seasonal transition period, while TP surface temperature increased significantly and showed early signal compared to the surroundings with the global warming. Therefore, considerable attention must be paid to the location and strength of the WJ with respect to the sensible heat flux over the TP