Magnetic meridional winds in the thermosphere obtained from Global Assimilation of Ionospheric Measurements (GAIM) model

Abstract

Thermospheric neutral winds play an important part in the dynamics of ionospheric plasma and represent one of the key inputs for ionospheric physics‐based models. Yet wind measurements are scarce and generally lack global coverage and continuity. To help mitigate this shortcoming, a data assimilation model was used to estimate neutral winds in the low‐ and middle‐latitude thermosphere. Seasonal global maps of NmF2 and hmF2 were generated from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation measurements for geomagnetically quiet and low solar flux conditions. The maps were assimilated into the Utah State University Global Assimilation of Ionospheric Measurements–Full Physics (GAIM‐FP) model. GAIM‐FP, which uses the physics‐based ionosphere‐plasmasphere model (IPM) and employs an ensemble Kalman filter technique, significantly improved the agreement between the modeled and measured NmF2 and hmF2 globally compared to the IPM. Global quiet time magnetic meridional winds were derived for December and June solstices and March equinox. The morphology of the derived winds was analyzed and validated by comparing with ground‐based measurements and with wind values from the empirical horizontal wind model. GAIM‐FP‐estimated winds were shown to be in good agreement with the wind observations. Furthermore, the sensitivity of the derived winds to uncertain parameters, including the O+‐O collision frequency, neutral composition, number of radio occultations, and data errors, was investigated. The uncertainties were found to have only small effects on the derived winds. The results of this work indicate that thermospheric wind estimation from GAIM‐FP is a valuable tool for wind specification over regions where limited or no wind measurements exist.

Calibration and Validation of Swarm Plasma Densities and Electron Temperatures Using Ground‐Based Radars and Satellite Radio Occultation Measurements

“…In addition to the COSMIC measurements, we also use plasma frequency data obtained from the University of Massachusetts, Lowell's (UML) DPS‐4/4D Digisondes (Reinisch et al, ), located at Jicamarca (12.0°S, 76.9°W), Sao Luis (2.6°S, 44.2°W), Fortaleza (3.9°S, 38.4°W), Sanya (18.3°N, 109.4°E), and Guam (13.6°N, 144.9°E). These are equatorial and low‐latitude stations where the ionospheric F region peak altitude, h m F 2 , is usually the highest (e.g., see Burns et al, ; Lomidze et al, ), and since the ionosondes are limited to making measurements only up to the altitude of h m F 2 , these sites have the largest probability of having nearly coincident measurements of plasma frequency up to the altitude of the Swarm satellite. Note that we did not use theoretically extrapolated data above h m F 2 , which are also available.…”

Estimation of thermospheric zonal and meridional winds using a Kalman filter technique

“…These three stations were chosen because they have extensive nighttime wind observations over several decades [e.g., Emmert et al , , and references therein] and span the latitudinal range from equatorial to middle latitudes, albeit are on a similar meridian. All FPI wind data used in this study were obtained from the Madrigal database (http://www.openmadrigal.org/), and seasonal averages (for December and June solstices, and March equinox) were not only calculated for similar geophysical conditions as in the case of the COSMIC data but also included wind data from previous solar cycles [ Lomidze et al , ]. The error bars correspond to one standard deviation and indicate normal quiet time geophysical variability.…”

“…One of the main input into TWAM is the magnetic meridional wind data from GAIM‐FP [ Lomidze et al , ]. The magnetic meridional wind ( v mag , positive toward magnetic north) has contributions from geographic zonal ( u , positive eastward) and meridional ( v , positive northward) winds and is generally expressed as [ Titheridge , ]: …”

“…These methods include the so‐called servo models [ Rishbeth et al , ], which use measurements of ionospheric F 2 layer peak parameters, and the wind derivation from Incoherent Scatter Radar (ISR) measurements of plasma velocities along the magnetic field [ Salah and Holt , ]. Recently, Scherliess et al [] and Lomidze et al [] have reported about a new method to estimate thermospheric magnetic meridional winds using an ionospheric data assimilation model. The method was shown to be reliable, capable to accurately represent wind climatology, and different from servo and ISR methods, provides wind values over the entire low‐ and middle‐latitude regions.…”

“…The recent availability of global magnetic meridional wind and electron density data from the Global Assimilation of Ionospheric Measurements Full Physics (GAIM‐FP) model [ Lomidze et al , ] provides a new opportunity to use the GAIM‐FP derived wind data together with a thermospheric wind model to extract information about the zonal and meridional components of the wind. For this purpose, the GAIM‐FP data and the wind model needs to be combined in an optimal fashion.…”