Seasonal variations of gravity‐wave parameters over the northern and southern Tibetan plateau radiosonde observatory

Abstract

AbstractSeasonal variations of gravity‐wave parameters over the northern and southern Tibetan Plateau are studied using high vertical‐resolution L‐band radiosonde data during the period 2014 to 2019. The wave parameters include wavelength, frequency, phase speed, group velocity, perturbation energies and momentum fluxes. The synoptic effects on the gravity‐wave parameters are discussed and assessed with the Pearson correlation. The tropospheric vertical wavelengths as estimated from the zonal wind perturbation were found to show a pronounced decrease over the southern Tibetan Plateau in the warm season. The tropospheric (stratospheric) horizontal wavelength is shortest (longest) in summer, and the stratospheric horizontal wavelength is longer than the tropospheric horizontal wavelength. The ratio of the intrinsic frequency to the Coriolis parameter is 2.5–5 (2–4.5) with a summer (winter) maximum in the troposphere (lower stratosphere). The ratio is generally higher in the north than in the south. The typical value of the mean tropospheric (stratospheric) intrinsic‐phase speed is 3.5–6 (2–11) m·s−1. The mean intrinsic‐phase speed in the south is mostly larger than that in the north. The tropospheric zonal ground‐based group velocities are dominantly eastward in all seasons. The stratospheric zonal ground‐based group velocity shifts from eastward in summer to westward in winter. In the troposphere, the seasonal cycles of the kinetic energy (KE) and potential energy (PE) exhibit regional differences. The tropospheric vertical fluctuation energy (VE) is independent of both season and region. The stratospheric KE, PE and VE are smaller in the warm season. The negative zonal momentum flux and positive meridional momentum flux are strongest in winter and summer.