Gravity wave analysis of four years of high vertical resolution United States radiosonde data

Atmospheric gravity wave information has been derived from four years (1998–2001) of high vertical resolution U.S. radiosonde wind and temperature data. Some of the results reinforce earlier analyses using various methods while others represent new findings. Interpretations are given for some of the results whereas some remains to be done to explain the other results. (1) On the average, lower stratospheric gravity wave energies decrease poleward and are stronger in (Northern Hemisphere) winter than summer. This pattern holds from 7°N to 72°N. (2) Tropospheric gravity waves are also stronger in winter than summer, but they maximize at middle latitudes (35°–40°N). (3) In the troposphere, gravity wave energy maxima exist over the Rocky Mountains. In the lower stratosphere the energy maxima are mostly in the southeastern U.S. (4) QBO and ENSO effects appear to account for much of the observed interannual variability in lower stratospheric gravity wave energies. (5) The 12-hourly time series of tropospheric and lower stratospheric gravity wave energies are virtually uncorrelated with each other (correlation ∼0.15 or less on the average). (6) Most dominant gravity wave intrinsic frequencies divided by f are around 3.9 in the troposphere, and 2.4–3 in the lower stratosphere. In the lower stratosphere, generally decreases weakly with increasing latitude. (7) Most dominant gravity wave vertical wavelengths decrease with increasing latitude in the lower stratosphere, and they maximize at mid-latitudes (35°–40°N) in the troposphere. In both the troposphere and lower stratosphere, the vertical wavelengths are longer in winter and shorter in summer. (8) Most dominant gravity wave horizontal wavelengths decrease with increasing latitude in both the troposphere and lower stratosphere, with larger values in the lower stratosphere. (9) Approximately 50% of the tropospheric gravity waves show upward energy propagation, whereas there is about 75% upward propagation in the lower stratosphere. The lower stratospheric percentage is generally smaller in winter and bigger in summer, especially at mid- and high-latitudes. (10) In the lower stratosphere, the dominant gravity wave horizontal propagation direction is eastward south of 25°N and westward north of 25°N. Waves are relatively more isotropic in the troposphere. Moreover, waves are found to be more anisotropic in winter in the lower stratosphere.