Using GPS radio occultations to infer the water vapor feedback. Issue 22 (26th November 2016)

• Record Type: Journal Article
• Authors: Vergados, Panagiotis; Mannucci, Anthony J.; Ao, Chi O.; Fetzer, Eric J.
• Is Part Of: Geophysical research letters. Volume 43:Issue 22(2016)
• Page Start: 11, 841
• Page End: 11, 851
• Publication Date: 2016-11-26
• Subjects: upper troposphere -- water vapor feedback -- air refractive index -- radio occultation -- GPS -- COSMIC; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL071017
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The air refractive index at L ‐band frequencies depends on the air's water vapor content and density. Exploiting this relationship, we derive for the first time a theoretical model to infer the specific humidity response to surface temperature variations, d q /d Ts, given knowledge of how the air refractive index and temperature vary with surface temperature. We validate this model by using 1.2–1.6 GHz Global Positioning System Radio Occultation (GPS RO) observations from 2007 to 2010 at 250 hPa, where the water vapor feedback on surface warming is strongest. The d q /d Ts estimation from GPS RO observations shows excellent agreement with previously published results and the responses estimated by using the Atmospheric Infrared Sounder and the NASA's Modern‐Era Retrospective Analysis for Research and Applications data sets. Because of their high sensitivity to fractional changes in water vapor, current and future GPS RO observations show great promise in monitoring climate feedback and their trends. Key Points: We present a novel approach to measure water vapor feedback by using air's refractive index We estimate for the first time the water vapor feedback by using COSMIC observations The GPS‐based water vapor feedback is in excellent agreement with independent estimates