Understanding the dominant intraseasonal modes of the springtime primary diabatic heating over the eastern Tibetan Plateau

Before establishment of the Asian summer monsoon, the spring diabatic heating over the Tibetan Plateau (TP) is regarded as an essential factor to modulate rainfall in the surrounding and downstream regions of the TP, but its intraseasonal variability (ISV) has not been paid enough attention to. Based on the observation and ERA5 reanalysis data, the first two leading modes of the spring ISV of the surface sensible heat (SH) and the latent heat of condensation (LH) over the eastern TP have been identified, which both exhibit a north-south dipole and uniform pattern with dominant similar to 40-day and 10-20-day periods, respectively. The ISV of LH is strongly negatively correlated to that of SH, which is determined by variations of ground-air temperature difference. The north-south dipole patterns for the 40-day period are induced by the synergistic effect of northward-propagating circulation anomalies from the tropical Indian Ocean and a southeastward-propagating wave train in the middle-to-high latitudes, whereas the uniform patterns can be attributed to an eastward-propagating zonal wave train in the mid-latitude. Accompanied with the ISV of SH and LH, the anomalous moisture convergence/divergence and thus rainfall anomalies occur in the Yangtze River Basin. These results suggest that the spring diabatic heating over the eastern TP has great potentials as a predictability source of anomalous precipitation in its downstream regions on intraseasonal timescale.