Magnitudes of Gravity Wave Pseudomomentum Flux Derived by Combining COSMIC Radio Occultation and ERA-Interim Reanalysis Data

Xu Xu,Li Li,Luo Luo,Yu Yu

doi:10.3390/atmos10100598

Abstract

In the present work, dry temperature profiles provided by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) mission and the horizontal wind field provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis are combined for the first time to retrieve the magnitudes of gravity wave (GW) pseudomomentum flux (PMF). The vertical wave parameters, including Brunt–Väisälä frequencies, potential energy (Ep), and vertical wavelengths, are retrieved from RO temperature profiles. The intrinsic frequencies, which are retrieved from the horizontal wind field of ERA-Interim, are combined with the vertical wave parameters to derive the horizontal wavelengths and magnitudes of the PMF of GWs. The feasibility of this new strategy is validated first by comparing the distributions of GW parameters during June, July, and August (JJA) 2006 derived this way with those derived by previous studies. Then the seasonal and interannual variations of the distributions of GW PMF for three altitude ranges, 20–25 km, 25–30 km, and 30–35 km, over the globe during the seven years from June 2006 to May 2013 are presented. It is shown that the three altitude intervals share similar seasonal and interannual distribution patterns of GW PMF, while the magnitudes of GW PMF decrease with increased height and the hot spots of GW activity are the most discernable at the lowest altitude interval of 20–25 km. The maximums of PMF usually occur at latitudes around 60° in the winter hemispheres, where eastward winds prevail, and the second maximums exist over the subtropics of the summer hemispheres, where deep convection occurs. In addition, the influence of quasi-biennial oscillation (QBO) on both GW PMF and zonal winds is discernible over subtropical regions. The present work complements the GW PMF interannual variation patterns derived based on satellite observations by previous studies in terms of the altitude range, latitude coverage, and time period analyzed.

Highlights

It is well known that gravity waves (GWs) play an important role in middle-atmospheric circulation by transporting energy and momentum in their vertical or horizontal propagations [1,2], and GW parameterizations form a key component of climate and weather models [3,4]
The results presented in this work demonstrate that combining temperature profiles dominates, quasi-biennial oscillation (QBO) is evident in the temporal variation of both wind fields from COSMIC radio occultation (RO) and horizontal winds from ERA-Interim reanalysis is a feasible way to study the and GW pseudomomentum flux (PMF) values at the altitude range of 20–25 km
A new strategy is presented in the present study to derive GW PMF by combing RO temperature data and model wind data from ERA-Interim

Summary

Introduction

It is well known that gravity waves (GWs) play an important role in middle-atmospheric circulation by transporting energy and momentum in their vertical or horizontal propagations [1,2], and GW parameterizations form a key component of climate and weather models [3,4]. Among all the parameters that characterize GW activities, the vertical flux of horizontal momentum, or momentum flux (MF), is the most prominent, because it is crucial for estimating the level of wave breaking and the effect of GWs on mean flow [5,6]. Compared with measurements from other traditional techniques, the large amount of temperature profiles provided by GPS RO missions, which have high precision, high vertical resolution, global coverage, and long-term stability, enable a thorough understanding of the mesoscale perturbations caused by GWs over the globe [10,14]. The global distributions of GW potential energy have been investigated based on data from different RO missions including GPS/Meteorology (GPS/MET) [15], Challenging Minisatellite Payload (CHAMP) [16,17], Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) [18,19], and MetOp [20]. The latitudinal variations of RO-derived vertical wavenumber spectra of GWs were studied, and evidence of the interaction between vertically propagating convectively generated GWs and background mean flow were demonstrated [16,22]

Methods

Results

Discussion

Conclusion