Simulation of the Effect of Water-vapor Increase on Temperature in the Stratosphere

To analyze the mechanism by which water vapor increase leads to cooling inthe stratosphere, the effects of water-vapor increases on temperature in thestratosphere were simulated using the two-dimensional, interactive chemicaldynamical radiative model (SOCRATES) of NCAR. The results indicate thatincreases in stratospheric water vapor lead to stratospheric cooling, withthe extent of cooling increasing with height, and that cooling in the middlestratosphere is stronger in Arctic regions. Analysis of the radiationprocess showed that infrared radiative cooling by water vapor is a pivotalfactor in middle-lower stratospheric cooling. However, in the upperstratosphere (above 45 km), infrared radiation is not a factor in cooling;there, cooling is caused by the decreased solar radiative heating rateresulting from ozone decrease due to increased stratospheric water vapor.Dynamical cooling is important in the middle-upper stratosphere, anddynamical feedback to temperature change is more distinct in the NorthernHemisphere middle-high latitudes than in other regions and significantlyaffects temperature and ozone in winter over Arctic regions. Increasingstratospheric water vapor will strengthen ozone depletion through thechemical process. However, ozone will increase in the middle stratosphere.The change in ozone due to increasing water vapor has an important effect onthe stratospheric temperature change.