quasi-two day wave in the Northern Hemisphere

Abstract. Thisstudyusesglobalsynopticmeteorologicalfieldsfroma 5 high-altitudedataassimilationsystemtoinvestigatethespatialandtem- 6 poralcharacteristicsofthequasi-2daywave(Q2DW)andmigratingdiur- 7 naltideduringtheNorthernHemispheresummersof2007,2008,and2009. 8 Byapplyinga2-dimensionalfastFouriertransformtomeridionalwindand 9 temperaturefields,weareabletoidentifyQ2DWsourceregionsandtodi- 10 agnosepropagationofQ2DWactivityintotheuppermesosphereandlower 11 thermosphere.WefindthatQ2DWiscomprisedprimarilyofwestwardprop- 12 agatingzonalwavenumber3andwavenumber4componentsthatoriginate 13 fromwithinbaroclinicallyunstableregionsalongtheequatorwardflankof 14 thesummermidlatitudeeasterlyjet.Amplitudevariationsofwavenumbers 15 3and4tendtobeanti-correlatedthroughoutthesummer,withwavenum- 16 ber3maximizinginJulyandwavenumber4maximizinginlateJuneandearlyAugust.MonthlymeanQ2DWamplitudesbetween30 ◦ –50 ◦ Nlatitude 1718 arelargestwhendiurnaltidalamplitudesaresmallestandviceversa.How- 19 ever,thereisnoevidenceofanyrapidamplificationoftheQ2DWvianon-