Global “warming holes” and regional land surface-atmosphere interactions

A summer daytime “warming hole (WH)” in the central U.S. was identified observationally in the last quarter of the 20th century as well as in a regional model's future scenario climate in mid-21st century. In this study we report the finding of additional major summer WHs (i.e., cooling centers) in south-eastern China and central South America that occurred in the 20th century. In addition, we found that the U.S. WH extends up to the lower troposphere and have existed for the most time of the 20ty century. All the three WHs are located downstream of the world's predominant low-level jets (LLJ) areas where mesoscale convective systems (MCSs) produce heavy summer rainfall on regions of intensive agriculture. Increased LLJ-related moisture convergence in the WH regions enhanced cloudiness and thus resulted in larger attenuation of daytime solar radiation, partly explaining the opposite trends in daily maximum and minimum temperatures in the WHs during summer. The prominent MCS activity in WH regions increased rainfall and moist in soil, thus reducing the daytime sensible heating and resulting in cooling nears surface.