Processes determining the seasonality of accelerated Tibetan Plateau warming during recent decades

The accelerated surface air warming of Tibetan Plateau (TP) greatly alters the local cryosphere and ecosystem. The TP warming exhibits prominent seasonality, but the processes determining the seasonality remain unclear. This study investigates the issue from an energy budget perspective through analyzing air temperature budget and surface energy balance. The warming is relatively weak in summer and spring, while it becomes strong in autumn and winter. In summer and autumn, the warming is mainly driven by outside forcing processes. Anomalous summertime reduction of precipitation over western North Pacific triggers a circumglobal wavetrain that warms TP by increasing heat transport. In autumn, the superposition of zonal and meridional wavetrains enhances anomalous heat transporting into TP, intensifying the warming. The strongest wintertime warming is contributed jointly by outside forcing and local feedbacks. The outside forcing is due to atmospheric warming over the Barents Sea, which triggers a meridional wavetrain to transport heat into TP. Two local feedback processes enhance sensible heating to heat air by warming surface. Firstly, reduced snow cover increases surface-absorbed solar radiation through the snow-albedo feedback. Secondly, the surface warming tends to strengthen evaporation and moisten the atmosphere aloft, which increases downward longwave radiation and causes a further surface warming, forming a local moisture process feedback. In spring, the changes of outside forcing process have negligible impacts on the warming of TP, the warming is mainly contributed by increases of sensible heating, which is supported by increased surface absorption of radiation fluxes due to the two local feedback processes.