Estimating Eliassen‐Palm flux using COSMIC radio occultation

Abstract

We present a methodology for analyzing the Eliassen‐Palm (E‐P) flux in the troposphere and stratosphere using GPS radio occultation data from the COSMIC project. In this methodology, geopotential height and temperature are mapped on constant pressure surfaces using a Bayesian interpolation scheme with a spherical harmonic basis, and the components of the E‐P flux are evaluated using geostrophic winds. We perform a simulation‐analysis study using the NCEP/NCAR Reanalysis as truth. E‐P fluxes are evaluated daily, and it is found that patterns of E‐P flux are estimated faithfully, and extrema in the vertical and horizontal components are underestimated by 5–10% and by 30–40%, respectively. Monthly hemispheric averages of the vertical component of the E‐P flux at the tropopause can be estimated to <5%. The error is due to the geostrophic approximation and spatial coverage, mostly the latter: COSMIC GPS radio occultation only resolves atmospheric eddies with scales greater than 1000 km on a daily basis.