Simultaneous lidar observations of temperatures and waves in the polar middle atmosphere on the east and west side of the Scandinavian mountains: a case study on 19/20 January 2003

[摘要] Atmospheric gravity waves have been the subject of intenseresearch for several decades because of their extensive effects onthe atmospheric circulation and the temperature structure. TheU. Bonn lidar at the Esrange and the ALOMAR RMR lidar at the AndøyaRocket Range are located in northern Scandinavia 250 km apart onthe east and west side of the Scandinavian mountain ridge. DuringJanuary and February 2003 both lidar systems conductedmeasurements and retrieved atmospheric temperatures. On19/20 January 2003 simultaneous measurements for more than7 h were possible. Although during most of the campaign time theatmosphere was not transparent for the propagation oforographically induced gravity waves, they were neverthelessobserved at both lidar stations with considerable amplitudesduring these simultaneous measurements. And while the source ofthe observed waves cannot be determined unambiguously, theobservations show many characteristics of orographically excitedgravity waves. The wave patterns at ALOMAR show a randomdistribution with time whereas at the Esrange a persistency in thewave patterns is observable. This persistency can also be found inthe distribution of the most powerful vertical wavelengths. Themode values are both at about 5 km vertical wavelength,however the distributions are quite different, narrow at theEsrange with values from λ_z=2–6 km and broad atALOMAR, covering λ_z=1–12 km vertical wavelength.In particular the difference between the observations at ALOMARand at the Esrange can be understood by different orographicconditions while the propagation conditions were quite similar. Atboth stations the waves deposit energy in the atmosphere withincreasing altitude, which leads to a decrease of the observedgravity wave potential energy density with altitude. Themeteorological situation during these measurements was differentfrom common winter situations. The ground winds were mostlynortherlies, changed in the upper troposphere and lowerstratosphere to westerlies and returned to northerlies in themiddle stratosphere.

[学科分类] 大气科学