Abstract
Abstract. Mean vertical velocity measurements obtained from radars at polar latitudes using polar mesosphere summer echoes (PMSEs) as an inert tracer have been considered to be non-representative of the mean vertical winds over the last couple of decades. We used PMSEs observed with the Middle Atmosphere Alomar Radar System (MAARSY) over Andøya, Norway (69.30∘ N, 16.04∘ E), during summers of 2016 and 2017 to derive mean vertical winds in the upper mesosphere. The 3-D vector wind components (zonal, meridional and vertical) are based on a Doppler beam swinging experiment using five beam directions (one vertical and four oblique). The 3-D wind components are computed using a recently developed wind retrieval technique. The method includes full non-linear error propagation, spatial and temporal regularisation, and beam pointing corrections and angular pointing uncertainties. Measurement uncertainties are used as weights to obtain seasonal weighted averages and characterise seasonal mean vertical velocities. Weighted average values of vertical velocities reveal a weak upward behaviour at altitudes ∼84–87 km after eliminating the influence of the speed of falling ice. At the same time, a sharp decrease (increase) in the mean vertical velocities at the lower (upper) edges of the summer mean altitude profile, which are attributed to the sampling issues of the PMSE due to disappearance of the target corresponding to the certain regions of motions and temperatures, prevails. Thus the mean vertical velocities can be biased downwards at the lower edge, and the mean vertical velocities can be biased upwards at the upper edge, while at the main central region the obtained mean vertical velocities are consistent with expected upward values of mean vertical winds after considering ice particle sedimentation.
Highlights
Knowledge of the neutral wind behaviour is one of the main interests in atmospheric sciences from the troposphere up to the thermosphere to investigate various dynamical processes
The aim of this study is mainly connected to vertical motions, the mean climatology of the vertical velocities and the relevance of using polar mesosphere summer echoes (PMSEs) as an inert traces to obtain neutral wind velocities
The reason for discrepancy of vertical velocity measurements in PMSE compared to the predictions from global circulation models has been explained by Hoppe and Fritts (1995b), who argued that the influence of background dynamics on appearance of PMSEs resulted in a bias on all measurements of vertical motion with radars
Summary
Knowledge of the neutral wind behaviour (or motion of the air) is one of the main interests in atmospheric sciences from the troposphere up to the thermosphere to investigate various dynamical processes. Improving temporal and spatial resolution of wind vector components is an important challenge for different observational techniques and data analysis. Such improvements are of particular importance in the vertical component, since the expected mean vertical velocities are in the range of a few centimetres per second, requiring more sophisticated observations as well as data analysis to obtain a reliable mean climatology. Mean vertical winds are known to be an important contributor to the thermal structure of the middle atmosphere and are related to the dynamical processes of the global seasonal pole-to-pole circulation (Garcia and Solomon, 1985; Becker, 2012; Smith, 2012). The underlying dynamical processes were firstly proposed by Lindzen (1981) and later parametrised by Holton (1982)
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