SAMI3/SD‐WACCM‐X simulations of ionospheric variability during northern winter 2009

Abstract

We have performed simulations using the Naval Research Laboratory's physics‐based model of the ionosphere, Sami3 is A Model of the Ionosphere (SAMI3), to illustrate how neutral wind dynamics is responsible for day‐to‐day variability of the ionosphere. We have used neutral winds specified from the extended version of the specified dynamics Whole Atmosphere Community Climate Model (SD‐WACCM‐X), in which meteorology below 92 km is constrained by atmospheric specifications from an operational weather forecast model and reanalysis. To assess the realism of the simulations against observations, we have carried out a case study during January–February 2009, a dynamically disturbed time characterized by a sudden stratospheric warming (SSW) commencing 24 January 2009. Model results are compared with total electron content (TEC) from Jet Propulsion Laboratory global ionospheric maps. We show that SAMI3/SD‐WACCM‐X captures longitudinal variability in the equatorial ionization anomaly associated with nonmigrating tides, with strongest contributions coming from the diurnal eastward wave number 2 (DE2) and DE3. Both migrating and nonmigrating tides contribute to significant day‐to‐day variability, with TEC varying up to 16%. Our simulation during the SSW period reveals that at the Jicamarca longitude (285°E) on 27 January 2009 nonmigrating tides contribute to an enhancement of the electron density in the morning followed by a decrease in the afternoon. An enhancement of the semidiurnal eastward wave number 2 (SE2) and SE3 nonmigrating tides, likely associated with the appearance of the SSW, suggests that these tides increase the longitudinal variability of the SSW impact on the ionosphere. The conclusion is that realistic meteorology propagating upward from the lower atmosphere influences the dynamo region and reproduces aspects of the observed variability in the ionosphere.

Day‐to‐day variability in the thermosphere and its impact on plasmasphere refilling

“…The SD‐WACCM‐X simulation also provided an example of day‐to‐day variability in thermosphere O densities. While the level of variability found in SD‐WACCM‐X (2.4%) is smaller than that required for the refilling rate effect of Figure (20%), we note that SD‐WACCM‐X captured only 50% of the measured day‐to‐day variability in TEC [ McDonald et al , ]. Further improvements to SD‐WACCM‐X modeling are expected to increase the day‐to‐day variability in densities and TEC.…”

“…The affect of SAMI3 ion motions on the SD‐WACCM‐X atmosphere was also not included in these simulations. Even with these limitations, 50% of the observed day‐to‐day variability in TEC was reproduced by the model during the period from 6 to 31 January 2009 [see McDonald et al , , Figure 3]. This coupled model therefore gives us an example of realistic, though incomplete, day‐to‐day variability in atmospheric winds and densities.…”

“…The coupling was limited to the effect of SD‐WACCM‐X winds on SAMI3 ion motions and on the wind‐driven dynamo potential. The effect of SD‐WACCM‐X atmospheric density values on the SAMI3 ionosphere was not included (instead observationally corrected NRLMSISE‐00 values were used, with fixed scalars [ McDonald et al , ]). The affect of SAMI3 ion motions on the SD‐WACCM‐X atmosphere was also not included in these simulations.…”

“…upon request (john.emmert@nrl.navy.mil). SD‐WACCM‐X zonal winds and oxygen densities are numerical information provided in figures; these are produced by solving the SD‐WACCM‐X equations; see McDonald et al [] for details. Numerical data for the figures above can be obtained by contacting J.K. Orbit data were obtained from http://www.space-track.org; the derived thermospheric densities are available from Emmert [].…”

Multimodel comparison of the ionosphere variability during the 2009 sudden stratosphere warming

“…The ionospheric variability during SSWs is considered to be primarily driven by changes in atmospheric tides. In particular, enhancements in the solar semidiurnal migrating tide ( S W 2), westward propagating semidiurnal nonmigrating tide with zonal wave number 1 ( S W 1), and lunar semidiurnal migrating tide ( M 2) are considered to be the dominant drivers of the ionosphere variability [ Fang et al , ; Pedatella and Liu , ; McDonald et al , ]. In the case of the S W 2 and M 2, the tidal enhancements are the result of changes in the zonal mean atmosphere which impact the tidal propagation and/or result in a quasi‐resonant state of the atmosphere at the M 2 period [ Jin et al , ; Forbes and Zhang , ].…”