Influences of Boreal Summer Intraseasonal Oscillation on Heat Waves in Monsoon Asia

By analyzing observation-based high-resolution surface air temperature (SAT) data over the Asian monsoon region (here called “monsoon Asia”) for 1981–2007, the modulation by boreal summer intraseasonal oscillation (BSISO) of heat wave (HW) occurrence is examined. Strong SAT variability and a high probability of HW occurrence on intraseasonal time scales are found consistently in the densely populated regions over central India (CI), the Yangtze River valley in China (YR), Japan (JP), and the Korean Peninsula (KP). The two distinct BSISO modes (30–60-day BSISO1 and 10–30-day BSISO2) show different contributions to HW occurrence in monsoon Asia. A significant increase in HW occurrence over CI (YR) is observed during phases 2–3 (8–1) of BSISO2 when the 10–30-day anticyclonic and descending anomaly induce enhanced upward thermal heating and sensible heat flux (warm advection) around the areas. On the other hand, the northeastward propagating BSISO1 is closely connected to the increased HW probability ...