HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds

dc.contributor.authorMalhotra, Garimaen
dc.contributor.committeecochairBaker, Joseph B. H.en
dc.contributor.committeecochairRuohoniemi, J. Michaelen
dc.contributor.committeememberScales, Wayne A.en
dc.contributor.committeememberClauer, Robert C.en
dc.contributor.departmentElectrical and Computer Engineeringen
dc.description.abstractThe equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling between QBO and the polar vortex has been extensively studied over the past few decades, however, less is known about QBO influences in the mid-latitude mesosphere. One reason for this is the relative lack of instrumentation available to study mesospheric dynamics at mid-latitudes. In this study, we have used the mid-latitude SuperDARN HF radar at Saskatoon (52.16 N, -106.53 E) to study inter-annual variation in mesospheric winds. The specific aim was to determine whether or not a Quasi Biennial signature could be identified in the Saskatoon mesosphere, and if so, to understand its relationship with the equatorial stratospheric QBO. To achieve this goal, a technique has been developed which extracts meteor echoes from SuperDARN near-range gates and then applies least-squares fitting across all radar beam directions to calculate hourly averages of the zonal and meridional components of the mesospheric neutral wind. Subsequent analysis of 13 years (2002-2014) of zonal wind data produced using this technique indicates that there is indeed a significant QBO signature present in Saskatoon mesospheric winds during late winter (Jan-Feb). This mesospheric QBO signature is in opposite phase with the equatorial stratospheric QBO, such that when QBO (at 50 hPa) is in its easterly (westerly) phase, the late winter winds in Saskatoon mesosphere become more (less) westerly. To further examine the source of the signature, we also analyzed winds in the Saskatoon stratosphere between 5 hPa and 70 hPa using the ECMWF ERA-Interim reanalysis data set, and found that the late winter stratospheric winds become less (more) westerly when QBO is easterly (westerly). This QBO signature in the mid-latitude stratospheric winds is essentially the same as that observed for the polar vortex in previous studies but it is opposite in phase to the mid-latitude mesospheric QBO. We therefore conclude that filtering of gravity waves through QBO-modulated stratospheric winds plays a major role in generating the mesospheric QBO signature we have identified in the Saskatoon HF radar data. When the Saskatoon stratospheric winds are anomalously westward during easterly QBO, the gravity waves having westward momentum might be filtered out, depositing a net eastward momentum in the mesosphere as they propagate upwards. This would result in increased westerly mesospheric winds at Saskatoon. The opposite would happen when the equatorial QBO is westerly.en
dc.description.degreeMaster of Scienceen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.subjectHF Radar Meteor echoesen
dc.subjectSuperDARN radaren
dc.subjectGravity wave filteringen
dc.subjectMesospheric QBOen
dc.subjectMid-Latitude QBOen
dc.subjectHolton Tanen
dc.subjectSuperDARN Radar Mesospheric windsen
dc.titleHF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Windsen
thesis.degree.disciplineElectrical and Computer Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.nameMaster of Scienceen


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