Surface Atmosphere Interactions and Heatwaves

This chapter considers the nature of the interactions between land and water surfaces and the overlying atmosphere involved in the development of heatwaves. It begins by defining the concept of the “active surface,” the three-dimensional interface that exchanges heat, mass, and momentum with the atmosphere noting that this surface is dynamic, exhibiting significant diurnal and seasonal variations in its characteristics. The chapter then explores the structure and dynamics of the atmospheric boundary layer (ABL) where much of the exchange of heat, mass and momentum that influences heatwave development occurs, highlighting how surface conditions and atmospheric stability influence heatwave development. A significant portion of the chapter is dedicated to the controls on heat, mass, and momentum exchanges between the surface and the atmosphere and the implications of these for heatwave development. Also addressed is the impact of soil moisture on heatwave intensity, noting that dry soils can exacerbate heatwaves by increasing sensible heat flux and reducing evaporative cooling. Further to the development of atmospheric heatwaves, the role of surface atmosphere interactions for marine heatwave development is discussed with a focus on the surface mixed layer of water bodies and the processes that lead to temperature anomalies. The importance of air-sea heat fluxes, oceanic heat advection, and vertical mixing in the formation and persistence of marine heatwaves is highlighted. Uniquely the surface atmosphere interactions considered important for lake and stream heatwaves are also considered in this chapter. In conclusion, the chapter underscores the complexity of surface-atmosphere interactions and their critical role in heatwave dynamics. It calls for a nuanced understanding of these processes to improve our interpretation of the development processes associated with specific atmospheric, marine, lake or stream heatwave events.