Short vertical-wavelength inertia-gravity waves generated by a jet–front system at Arctic latitudes – VHF radar, radiosondes and numerical modelling

摘要

Inertia-gravity waves with very short vertical wavelength (λ≤1000 m)are a very common feature of the lowermost stratosphere asobserved by the 52 MHz radar ESRAD (Esrange MST radar) in northern Scandinavia (67.88° N,21.10° E). The waves are seen most clearly inradar-derived profiles of buoyancy frequency (). Here, we present a casestudy of typical waves from 21 February to 22 February 2007. Goodagreement between derived from radiosondes and by radar shows thevalidity of the radar determination of . Large-amplitude wavesignatures in are clearly observed by the radar and the radiosondes inthe lowermost stratosphere, from 9 km to 14–16 km height. Vertical profilesof horizontal wind components and potential temperature from the radiosondesshow the same waves. Mesoscale simulations with the Weather Research andForecasting (WRF) model are carried out to complement the analysis of thewaves. Good agreement between the radar and radiosonde measurements and themodel (except for the wave amplitude) shows that the model gives realisticresults and that the waves are closely associated to the upper-level frontin an upper-troposphere jet–front system. Hodographs of the windfluctuations from the radiosondes and model data show that the wavespropagate upward in the lower stratosphere confirming that the origin of thewaves is in the troposphere. The observations and modelling all indicatevertical wavelengths of 700 ± 200 m. The radiosonde hodograms indicatehorizontal wavelengths between 40 and 110 km and intrinsic periods between 6and 9 h. The wave amplitudes indicated by the model are however an order ofmagnitude less than in the observations. Finally, we show that the profilesof measured by the radar can be used to estimate wave amplitudes,horizontal wavelengths, intrinsic periods and momentum fluxes which areconsistent with the estimates from the radiosondes.