Positive and negative surface feedback and atmospheric control of land surface conditions on convective organization over the Tibetan Plateau

The dependence of the feedback signal on atmospheric conditions is still poorly understood and may lead to an underestimation of feedback strength due to opposite responses of precipitation to soil moisture. Based on data from observation stations on the Tibetan Plateau and from satellites, this study evaluated the response of convective clouds to the change of evaporation fraction (EF) and analyzed how surface conditions affect the initiation and development of convection in different coupling regimes. After considering coupling regimes classified by the tropospheric state, the afternoon convective cloud showed a strong response to EF, which is negative feedback in the dry coupling regime and positive feedback in the wet coupling regime. Organized deep convection defined by both the cloud properties and the afternoon precipitation displayed this phenomenon. This shows that the lack of a strong response of convection to EF is due to the dependence of this response on the coupling regime, rather than on the method of defining convection. We also found that the difference in surface heat flux between the two regimes is more significant in the afternoon, while the difference of meteorological elements is most significant before noon. These results provide support for the use of ground-based meteorological data to determine coupling regimes. We also used a regression tree to decompose the effects of coupling regimes and EF into basic near-surface meteorological elements, the results of which provide support for some of our conclusions.