Observed Responses of Mesospheric Water Vapor to Solar Cycle and Dynamical Forcings

Abstract

Abstract This study focuses on responses of mesospheric water vapor (H 2 O) to the solar cycle flux at Lyman‐α wavelength and to dynamical forcings according to the multivariate El‐Nino/Southern Oscillation (ENSO) index. The zonal‐averaged responses are for latitudes from 60°S to 60°N and pressure‐altitudes from 0.01 to 1.0 hPa, as obtained from multiple linear regression analyses of time series of H 2 O from the Halogen Occultation Experiment for July 1992 to November 2005. The results compare very well with those from a separate simultaneous temporal and spatial (STS) method that also confirms that there are no significant sampling biases affecting both sets of results. Distributions of the seasonal amplitudes for temperature and H 2 O are in accord with the seasonal net circulation. In general, the responses of H 2 O to ENSO are anticorrelated with those of temperature. H 2 O responses to multivariate ENSO index are negative in the upper mesosphere and largest in the Northern Hemisphere; responses in the lower mesosphere are more symmetric with latitude. H 2 O responses to the Lyman‐α flux (Lya) vary from strong negative values in the uppermost mesosphere to very weak, positive values in the tropical lowermost mesosphere. However, the effects of those H 2 O responses to the solar activity extend to the rest of the mesosphere via dynamical processes. Profiles of the responses to ENSO and Lya also agree reasonably with published results for H 2 O at the low latitudes from the Microwave Limb Sounder.