Abstract
Global observations of gravity waves have been performed using the High Resolution Dynamics Limb Sounder (HIRDLS) temperature data. A background field that was derived by dynamically calculating 31 day (±15 day) means to block the stationary component and the slowly varying planetary‐scale waves, was first subtracted from the HIRDLS temperature measurements. An additional step was then taken to remove rapidly moving planetary‐scale waves by developing an along‐track temperature filter, which was created by averaging the profiles within a 1000 km along‐track window. Finally, each individual temperature perturbation vertical profile was analyzed using a fast Fourier transform to estimate gravity wave temperature amplitudes and vertical wavelengths. The investigation of the monthly mean gravity wave temperature amplitudes for the year 2006 found that gravity wave activity in the stratosphere is highly variable with season and can be very orographically dependent, especially in the winter extratropics. The monthly zonal means show that the peak vertical wavelengths correspond closely to the peak amplitudes. The increasing amplitudes and vertical wavelengths are faster and generated at lower altitudes in the winter extratropical and high‐latitude stratosphere than those in the summer tropical stratosphere. This is consistent with the lower source altitudes of orographic gravity waves in the extratropics and high latitudes and the higher source altitudes of convectively generated gravity waves in the tropics. Three cases were studied for the observed gravity waves over large mountain ranges using the European Centre for Medium‐Range Weather Forecasts wind data. Investigations of episodes of enhanced gravity wave activity over the southern Andes, the Cascade Range, and the Rockies in winter months of 2006 indicate that orographic gravity waves refract downwind from the mountains and propagate along the direction of the intense winds. By way of contrast, observations of gravity waves around the Himalayas show a strong relationship with the cyclones in that region.
Highlights
[26] Using the aforementioned data analysis method, the gravity wave temperature perturbations isolated from the High Resolution Dynamics Limb Sounder (HIRDLS) temperature measurements were analyzed for the whole year of 2006, over pressure levels from 121.15 hPa (∼15 km) to 0.215 hPa (∼60 km)
The enhanced gravity wave activity observed in different seasons in the tropics and the extratropics and high latitudes indicates that the waves in the tropics and the extratropical and high‐latitude zone are probably generated by different sources
[43] We extracted mesoscale gravity waves from HIRDLS temperature measurements using a new approach. Gravity wave properties such as horizontal amplitude and vertical wavelength were estimated by performing an fast Fourier transform (FFT) on each individual gravity wave temperature perturbation profile for pressures from 121.15 hPa (∼15 km) to 0.215 hPa (∼60 km)
Summary
[2] Atmospheric gravity waves modify the atmospheric circulation and influence the atmospheric thermal structure by transferring momentum from their sources, which are dominant in the troposphere and lower stratosphere, to anywhere between the troposphere and thermosphere, where they break or dissipate. Alexander et al [2008] demonstrated the ability of HIRDLS to observe gravity waves by analyzing one month of data (May 2006) They extracted gravity waves by removing the zonal mean temperatures and planetary‐. The comparisons with temperature profiles from high‐ resolution radiosondes, lidars, Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer, and European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses show similar systematic biases, that is, warmer bias at pressure levels between 100 and 5 hPa and colder bias at pressure levels between 5 and 1 hPa. Details about the evaluation and the qualities of the temperature data, as well as the ability to resolve small vertical scales, are described by Gille et al [2008]. The oscillation has been removed from the radiometric signals, but we should still give attention to this for gravity wave observations
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