Estimating 2D Neutral Wind Patterns Using Line-of-Sight Data from
Multiple Scanning Doppler Imagers
Abstract
We present a new analysis technique for estimating 2D neutral wind
pattern using data from a single Scanning Doppler Imager (SDI) or a
combination of SDIs, incoherent scatter radars (ISR) and Fabry-Perot
interferometers (FPI) within overlapping field-of-views. Neutral wind
plays an important role in ionospheric electrodynamics and
Ionosphere-Thermosphere coupling, by for example affecting the Joule
heating rates and plasma transport. However, reliable and extensive
measurements of the neutral wind are rather difficult to obtain.
Pointwise measurements can be obtained with ISRs or FPIs, but these
measurements can not provide 2D latitude-longitude maps of the neutral
wind pattern needed in mesospheric studies. A Scanning Doppler Imager
can measure the line-of-sight (LOS) component of the neutral wind in
dozens of directions simultaneously. However, further modeling is needed
to convert the LOS velocities into 2D velocity maps. Unfortunately these
maps are far from unique, as perpendicular velocities (e.g. rotation
around the measurement site) are not visible in the LOS data. This can
be mitigated by combining data from several nearby SDIs, or a
combination of SDIs, FPIs and ISRs. Our analysis technique is based on
fitting the LOS data with special vector basis functions called
Spherical Elementary Current Systems (SECS). In this approach the wind
is naturally divided into curl-free and divergence-free components, and
there is no need to provide any explicit boundary conditions on the wind
pattern. We present several synthetic test scenarios as well as first
results using data from SDIs located in Alaska. Using the synthetic test
scenarios we further estimate optimal locations for 2 or 3 SDIs that
could be located around the future EISCAT_3D radar system in northern
Scandinavia.