Abstract
Abstract. We revise selected findings regarding the utilization of Global Positioning System radio occultation (GPS RO) density profiles for the analysis of internal gravity waves (IGW), introduced by Sacha et al. (2014). Using various GPS RO datasets, we show that the differences in the IGW spectra between the dry-temperature and dry-density profiles that were described in the previous study as a general issue are in fact present in one specific data version only. The differences between perturbations in the temperature and density GPS RO profiles do not have any physical origin, and there is not the information loss of IGW activity that was suggested in Sacha et al. (2014). We investigate the previously discussed question of the temperature perturbations character when utilizing GPS RO dry-temperature profiles, derived by integration of the hydrostatic balance. Using radiosonde profiles as a proxy for GPS RO, we provide strong evidence that the differences in IGW perturbations between the real and retrieved temperature profiles (which are based on the assumption of hydrostatic balance) include a significant nonhydrostatic component that is present sporadically and might be either positive or negative. The detected differences in related spectra of IGW temperature perturbations are found to be mostly about ±10 %. The paper also presents a detailed study on the utilization of GPS RO density profiles for the characterization of the wave field stability. We have analyzed selected stability parameters derived from the density profiles together with a study of the vertical rotation of the wind direction. Regarding the Northern Hemisphere the results point to the western border of the Aleutian high, where potential IGW breaking is detected. These findings are also supported by an analysis of temperature and wind velocity profiles. Our results confirm advantages of the utilization of the density profiles for IGW analysis.
Highlights
Internal gravity waves (IGWs) play an essential role in atmospheric dynamics: they couple different atmospheric layers by their angular momentum transport (Egger et al, 2007); they impact large-scale circulation by interacting with the background flow (Fritts and Alexander, 2003); and, on smaller scales, their breaking leads to turbulent mixing of air (Fröhlich et al, 2007)
To verify this methodology applied to GRUAN data, we have applied the very same procedure on Global Positioning System radio occultation (GPS radio occultation (RO)) drydensity profiles provided by COSMIC Data Analysis and Archive Center (CDAAC) and compared our “retrieved” temperature profile to temperature profiles provided by CDAAC
The results indicate that the differences between the real and hydrostatic temperature profiles may vanish when all profiles are included in the average, probably due to the sporadic nature of the events with significant nonhydrostatic forcing
Summary
Internal gravity waves (IGWs) play an essential role in atmospheric dynamics: they couple different atmospheric layers by their angular momentum transport (Egger et al, 2007); they impact large-scale circulation by interacting with the background flow (Fritts and Alexander, 2003); and, on smaller scales, their breaking leads to turbulent mixing of air (Fröhlich et al, 2007). In comparison with temperature profiles, density profiles can provide more information about potential IGW breaking by calculation of specific stability parameters (Sacha et al, 2015). This is highly important for observational studies of the dynamical mechanisms that may support theories regarding IGW instability and breaking. The section introduces an update of the Sacha et al (2014) study with a focus on the comparison of IGW spectra derived from density and temperature profiles. 4. Specific variables derived from GPS RO data are analyzed to describe regions with potential IGW breaking and its connection to vertical rotation of the wind direction. The resulting distribution of the studied characteristics points mainly to the processes at the western border of the Aleutian high (AH)
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