Water Vapor and Ozone Variations in the Tropical Tropopause Layer during the Central Equatorial Pacific Experiment Campaign

Abstract

Water vapor and ozone profiles in the tropical tropopause layer (TTL) are investigated using measurements from balloon-borne frost-point hygrometers and ozone sensors during the Central Equatorial Pacific Experiment campaign. Variations in water vapor, ozone, and temperature are described during soundings taken over a period of two weeks and over a distance of approximately 2, 700 km along the equator. These observations indicate that the first and latter halves of the campaign period are characterized as cold and warm phases near the cold point tropopause, respectively. Stationary and eastward-traveling components equally contributed to these temperature anomalies. During the transition between the two phases, the ozone increased around 350–400 K, with the maxima around the 360 K isentrope. The water vapor simultaneously increased and decreased around the 360–400 K and 350–360 K isentropes, respectively. Simultaneous increases in ozone and water vapor around 360–400 K with a reduction in the vertical gradients suggest the possibility of turbulent mixing associated with a large-scale wave structure. The enhancement of vertical shear of zonal wind during the transition between the two phases also supports this idea. The decrease in water vapor around the 350–360 K isentropes could be understood as a result of saturation on the isentropic surface. This study shows the importance of observing variations in isentropic coordinates, rather than altitude coordinates, around the TTL in order to make a quantitative argument concerning mixing and dehydration when a large-amplitude disturbance exists.