First wind shear observation in PMSE with the tristatic EISCAT VHF radar

Abstract

The Polar Summer Mesosphere has the lowest temperatures that occur in the entire Earth system. Water ice particles below the optically observable size range participate there in the formation of strong radar echoes (Polar Mesospheric Summer Echoes, PMSE). To study PMSE we carried out observations with the European Incoherent Scatter (EISCAT) VHF and EISCAT UHF radar simultaneously from a site near Tromsø (69.58°N, 19.2272°E) and observed VHF backscattering also with the EISCAT receivers in Kiruna (67.86°N, 20.44°E) and Sodankylä (67.36°N, 26.63°E). This is one of the first tristatic measurements with EISCAT VHF, and we therefore describe the observations and geometry in detail. We present observations made on 26 June 2013 from 7:00 to 13:00 h UT where we found similar PMSE patterns with all three VHF receivers and found signs of wind shear in PMSE. The observations suggest that the PMSE contains sublayers that move in different directions horizontally, and this points to Kelvin‐Helmholtz instability possibly playing a role in PMSE formation. We find no signs of PMSE in the UHF data. The electron densities that we derive from observed incoherent scatter at UHF are at PMSE altitudes close to the noise level but possibly indicate reduced electron densities directly above the PMSE.

Multi-static spatial and angular studies of polar mesospheric summer echoes combining MAARSY and KAIRA

“…KAIRA was designed to study different kinds of atmospheric and ionospheric phenomena (Vierinen et al, 2013;McKay-Bukowski et al, 2015). KAIRA can be used as an all-sky imaging receiver for cosmic radio emissions to study D-region absorption (McKay et al, 2015) and as a phased array radar receiver (Virtanen et al, 2014) for nearby radar and radio transmitters, such as the EISCAT very high frequency (VHF) radar (Euro-pean Incoherent Scatter Scientific Association), MAARSY, or several nearby specular meteor radars.…”

Towards a Framework for Noctilucent Cloud Analysis

“…As a future research direction, this work can form the basis for synchronizing the optical observations from ground-based camera system with radar echoes from the EISCATincoherent scatter radar systems. While present radar observations provide limited information on the motion of the ice clouds [10], this will be significantly improved with the new volumetric radar system EISCAT_3D [33].…”

“…The polar mesospheric summer echoes (PMSE) radar echoes associated with polar ice clouds on the left[10] and optical image of Noctilucent clouds (NLC) on the right.…”

Observation of atomic oxygen O(1S) green‐line emission in the summer polar upper mesosphere associated with high‐energy (≥30 keV) electron precipitation during high‐speed solar wind streams

“…Moving forward, charge separation can be developed in the transition from PMSE to PMC. Extreme plasma drift speed of ≥300 m s −1 and supersonic velocity bring forth wind shear in PMSE/PMC regions, leading to Kelvin‐Helmholtz instability [e.g., Lee et al ., ; Mann et al ., ; Dalin et al ., ]. Wind shear is an important measure of the potential of squall line severity, which is usually associated with thunderstorms [ Rotunno and Klemp , ], since charge separation, squall, breakdown, and leader discharge of lightning are the consequential process in the tropospheric thunderclouds [ Rotunno and Klemp , ].…”

“…Moving forward, charge separation can be developed in the transition from PMSE to PMC. Extreme plasma drift speed of ≥300 m s À1 and supersonic velocity bring forth wind shear in PMSE/PMC regions, leading to Kelvin-Helmholtz instability [e.g., Lee et al, 2014;Mann et al, 2016;Dalin et al, 2010].…”