Diagnosing the ascending branch of the Brewer-Dobson circulation from measurements of water vapor
Speaker: Ken Minschwaner, New Mexico Institute of Mining and Technology
When: Wednesday, October 9, 2019, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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The Brewer-Dobson circulation (BDC) exerts a major influence on the distributions of key stratospheric compounds such as ozone, water vapor, and other radiatively important trace gases. One of the observational metrics for characterizing the circulation is the mean upward speed of air in the low-latitude, ascending branch of the BDC. Due to the very slow speeds involved (~20-50 m/day), direct measurements of this ascent are very challenging. We have developed methods for diagnosing mean upward speeds by tracking the phase lag of moist and dry anomalies in the tropical lower stratosphere, based on satellite measurements from the Aura Microwave Limb Sounder. A two-level time series approach will be described that uses daily mean data to derive upward speeds with an altitude resolution of 2-3 km in the lower stratosphere, and an effective temporal resolution of about 3 months over a time period of nearly 13 years. However, this method is not suitable for monthly mean water vapor observations in multi-decadal, multi-platform compilations such as the SWOOSH (Stratospheric Water and Ozone Satellite Homogenized) database. We outline an alternative approach that involves the propagation of anomalies in piecewise vertical profiles. We show that the profile method can be applied to SWOOSH water vapor to produce an accurate measure of mean upward speeds near 50 hPa, and to generate a nearly continuous record of upwelling in the tropical lower stratosphere from 1991 to present.
Ken Minschwaner is the Wilkening Professor of Physics at the New Mexico Institute of Mining and Technology, in Socorro NM. He has been on the faculty at New Mexico Tech since 1994. His research activities have included ground-based measurements of hydroxyl and total ozone, measurements from balloon-borne ozonesondes, satellite retrievals of thermospheric composition, spectroscopy and radiative transfer models, and analyses of satellite datasets for stratospheric dynamics, chemistry, and climate.