Climate Fact: Tropical Cyclones and Stratospheric Moisture
Increases in water vapor in the stratosphere (the second layer of the atmosphere extending from about ten to 30 miles in altitude) has implications for ozone, stratospheric temperatures, and surface temperatures. While more water vapor in the stratosphere leads to ozone depletion there and a slight cooling of surface temperatures, this cooling is more than compensated for by the surface warming resulting from the increased greenhouse effect. Observations indicate that at least the upper stratosphere has become “wetter” over the last few decades. Tropical cyclones may play an important role in stratospheric moisture trends. While tropical cyclones account for only about seven percent of the deep convection that occurs in the tropics, about 15 percent of the tropical moisture that reaches the stratosphere results from these events. In the Atlantic, tropical cyclones have become more frequent over the past 30 years. In the Pacific, where the tendency for cyclonic moisture to overshoot the stratosphere is the strongest, cyclones are most frequent during El Niño events. Three times as many cyclones form during El Niño than La Niña events.
Seasons: Summer, Fall
Sources: Romps, D and Kuan, Z. “Overshooting convection in tropical cyclones.” Geophysical Research Letters 36 (2009): L09804 and Shindell, DT. “Climate and ozone response to increased stratospheric water vapor.” Geophysical Research Letters 28 (2001): 1551-1554 and Matsuura, T et al. “A mechanism for interdecadal variability of tropical cyclone activity over the western North Pacific.” Climate Dynamics 21 (2003): 105-117 and Chan, JCL. “Interannual variations of intense typhoon activity.” Tellus 59A (2007): 455-460.
