Global observations of gravity waves from High Resolution Dynamics Limb Sounder temperature measurements: A yearlong record of temperature amplitude and vertical wavelength

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.