A Lagrangian Study of Tidal Advection of Mesospheric Water Vapor

Previous studies have demonstrated that the diurnal variability of mesospheric water vapor involves a non-linear interplay between dynamics, photochemistry, and catalytic processes. The inherent difficulty in measurement of winds and water vapor in this region makes the study of mesospheric water vapor complex. Here we study the sources of diurnal variability of mesospheric water vapor with the help of the specified dynamics configuration of the Whole Atmosphere Community Climate Model (WACCM) with thermosphere-ionosphere eXtension (SD-WACCM-X) for typical equinox conditions during the solar minimum year 2009. Special emphasis is given to the advective transport by the migrating diurnal tide and its impact on the mean water vapor in the mesosphere. To isolate the contribution from advective and non-advective processes, a Lagrangian parcel trajectory model is employed. Using this model, we incorporated the effect of both vertical and horizontal tidal advection on the diurnal variability of mesospheric water vapor. Our results indicate that the vertical tidal advection dominates the transport of water vapor in the upper mesosphere and that there is a significant contribution from horizontal tidal advection below 70 km. Among non-advective processes, chemical loss of water vapor has the largest contribution. The Lagrangian parcel trajectory approach is further extended using the recently released version 2.07 of water vapor observations from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument and dynamical tides from the empirical Climatological Tidal Model for the Thermosphere (CTMT). Differences in SD-WACCM-X and CTMT + SABER results are discussed in light of the veracity of SABER water vapor measurements.