Weakening sensible heat source over the Tibetan Plateau revisited: effects of the land-atmosphere thermal coupling

The bulk heat transfer coefficient (C (H) ) indicates the land-atmosphere thermal coupling strength. We seek to detect its variability and changes on the Tibetan Plateau (TP) during 1981-2006, particularly concerned with its effects on the sensible heat source. C (H) is parameterized by Monin-Obukhov similarity theory combining routine meteorological measurements. The South Asian monsoon period is characterized by weak sensible heat flux (H), but strong thermal coupling (C (H) ). Winter sees the greatest diurnal C (H) range, roughly 0.001-0.008. On average, C (H) exhibits a notable nighttime increase (10% decade(-1)) and a weak daytime decrease (-5% decade(-1)). The strengthening thermal coupling at selected sites alleviates the weakening of H, because it enhances nighttime H increase and reduces daytime H decrease. Moreover, we confirm the finding in earlier studies that sensible heating is weakening on the TP, but find its trend less notable than empirically estimated using C (H) = 0.004.