Dr Greg Holland
Greg Holland is Willis Senior Scientist in the Mesoscale and Microscale Meteorology Laboratory of NCAR, and Director of the Capacity Center for Climate and Weather Extremes C3WE. He has a long career meteorology including forecasting, teaching, research and community service – with the major focus being weather and climate extremes and unmanned aircraft. His publications have included major contributions to six textbooks and forecast manuals, together with over 120 research papers in atmospheric sciences and UAVs.
Tropical cyclones and the global energy budget: their role and implications
Greg Holland, Andreas Prein, and Cindy Bruyere
Capacity Center for Weather and Climate Extremes, NCAR
The bulk of the tropics are clear of clouds and continuously cool at a rate of 1-2oC per day and thermodynamic balance requires a vertical transport of moist enthalpy from the surface. In a landmark paper, Riehl and Malkus (1958) showed that tropical convection, or ‘Hot Towers’, provided a crucial vertical link in the maintenance of this tropical energy balance. A number of further studies have confirmed the link and updated the actual contribution of tropical convection.
Here we examine the relative roles of tropical cyclones compared to sustained active regions (such as the Indonesian Maritime Continent and the intertropical convergence zone), and other transient systems in maintaining this heat balance. We find that moist vertical motion in tropical cyclones is a major contributor, providing around 40% of the total required to maintain overall balance. As cyclones move away from the tropics and pass through the descending branch of the Hadley circulation, an interesting transformation occurs. The net vertical energy transport drops temporarily then returns towards previous levels, except now the bulk of the energy export is directed towards subtropical regions.
The implications of these findings for tropical cyclone activity in both current and future climate will be discussed.
Riehl, H., and J. Malkus, 1958: On the heat balance in the equatorial trough zone. Geophysica, 6, 503–538.