Ionosphere data assimilation modeling of 2015 St. Patrick's Day geomagnetic storm

Abstract

The ionospheric plasma disturbances during a severe storm can affect human activities and systems, such as navigation and HF communication systems. Therefore, the forecast of ionospheric electron density is becoming an important topic recently. This study is conducted with the ionospheric assimilation model by assimilating the total electron content observations into the thermosphere‐ionosphere coupling model with different high‐latitude ionospheric convection models, Heelis and Weimer, and further to forecast the variations of ionospheric electron density during the 2015 St. Patrick's Day geomagnetic storm. The forecast capabilities of these two assimilation models are evaluated by the root‐mean‐square error values in different regions to discuss its latitudinal effects. Results show the better forecast in the electron density at the low‐latitude region during the storm main phase and the recovery phase. The well reproduced eastward electric field at the low‐latitude region by the assimilation model reveals that the electric fields may be an important factor to have the contributions on the accuracy of ionospheric forecast.

Equatorial plasma bubble generation/inhibition during 2015 St. Patrick's Day storm

“…Chen et al . [, ] reported significant progress in reproducing storm time electron density and electric fields by assimilating TEC measurements with TIEGCM, and the root‐mean‐square error could be reduced by using rapid forecast cycles. They further showed that the assimilation results also provide much improved electric field forecast during quiet period by examining prereversal enhancement (PRE) of zonal electric fields [ Chen et al ., ].…”

“…Figure 2 Recently, there have been several attempts to examine possible EPB generation on a given night by computing RTI growth rate by using TIEGCM data [Carter et al, 2014a[Carter et al, , 2014bWu, 2015], with the results showing overall good agreement between larger growth rate and bubble occurrence, though some discrepancies were also pointed out, especially in a study related to the St. Patrick's Day storm, which are attributed to the lack of physically meaningful representation of prompt penetration electric fields in the model [Carter et al, 2016]. Chen et al [2016aChen et al [ , 2016b reported significant progress in reproducing storm time electron density and electric fields by assimilating TEC measurements with TIEGCM, and the root-mean-square error could be reduced by using rapid forecast cycles. They further showed that the assimilation results also provide much improved electric field forecast during quiet period by examining prereversal enhancement (PRE) of Rajesh et al [2017], are plotted in Figure 3.…”

“…While high‐latitude regions are more susceptible to direct impact, ionospheric storms can make the low‐latitude regions vulnerable by means of large‐scale electron density bite‐outs associated with plasma irregularities. One of such storms that caught the attention of ionospheric community is the one occurred on St. Patrick's Day in 2015, when planetary magnetic index ( Kp ) recorded a maximum of 8 and disturbance storm time index ( Dst ) reached as low as −223 nT [ Chen et al ., ]. The fact that several research articles have already been published, including special issues by journals, on the nature and impacts of this storm underscores the scientific community's interests in this space weather event, its influences, and associated ionospheric dynamics.…”

“…While this study attempts to examine the first question, significant improvement has already been reported recently in obtaining more realistic EPB growth rates [ Rajesh et al ., ], making use of the recent progress achieved by Chen et al . [, ] in forecasting the storm time ionospheric response by assimilating ground‐based Global Positioning System (GPS) total electron content (TEC) measurements to the TIEGCM, by means of employing rapid forecast cycles that appropriately updated the model neutral state vectors and produced more accurate electron density and electric field output.…”

“…Though there could be day-to-day variability in the EPB occurrence [Fagundes et al, 1999;Tsunoda, 2005Tsunoda, , 2006, considering the generation on consecutive four previous nights, and that irregularities were reported over Indian sector on the night of 17 March [Joshi et al, 2016;Tulasi Ram et al, 2016], the absence of EPB in this night over Taiwan seemed to be an apparent inhibition of the instability growth as a result of the ionospheric response to the storm. However, based on the growth rate of Rayleigh-Taylor instability (RTI) calculated using Thermosphere Ionosphere Electrodynamics Global Circulation Model (TIEGCM), Carter et al [2016] [Rajesh et al, 2017], making use of the recent progress achieved by Chen et al [2016aChen et al [ , 2016b in forecasting the storm time ionospheric response by assimilating ground-based Global Positioning System (GPS) total electron content (TEC) measurements to the TIEGCM, by means of employing rapid forecast cycles that appropriately updated the model neutral state vectors and produced more accurate electron density and electric field output.…”