Global equatorial plasma bubble growth rates using ionosphere data assimilation

Abstract

Flux tube integrated Rayleigh‐Taylor instability growth rates computed by using the results of ionosphere data assimilation are used for the first time to investigate global plasma bubble occurrence. The study is carried out by assimilating total electron content measurements using ground‐based Global Positioning System (GPS) receivers into thermosphere ionosphere electrodynamic general circulation model, and the growth rates are calculated by using standalone model run without assimilation (control run) as well as using prior (or forecast) state output of the assimilation run. The growth rates are compared with the rate of change of total electron content index (ROTI), estimated from global network of GPS receivers, as well as all‐sky airglow observations carried out over Taiwan on the nights of 16 and 17 March 2015. In contrast to the growth rates using the control run, results using data assimilation show remarkable agreement with the ROTI. Further, the all‐sky images reveal intense plasma bubbles over Taiwan on the night of 16 March, when the corresponding assimilated growth rate is also pronounced. Similarly, the absence of plasma bubbles in the all‐sky images on the night of 17 March (St. Patrick's Day storm) is supported by smaller growth rates predicted by the assimilation model. Significant improvements in the calculated growth rates could be achieved because of the accurate updating of zonal electric field in the data assimilation forecast. The results suggest that realistic estimate or prediction of plasma bubble occurrence could be feasible by taking advantage of the data assimilation approach adopted in this work.

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

“…Rajesh et al . [] demonstrated that the global RTI growth rates calculated using their data assimilation results agree well with corresponding ROTI values during both quiet and disturbed conditions.…”

“…Though the observations reveal intense bubble activity on all these nights, no EPB was observed over Taiwan on the night of 17 March 2015, when the St. Patrick's Day storm occurred [ Rajesh et al . [, Figure 3 (bottom panel)]].…”

“…The RTI growth rates calculated using this assimilated model results on the night of 17 March 2015, over the Taiwan and Indian longitudes as described by Rajesh et al . [], are plotted in Figure . Note that the Heelis high‐latitude empirical convection model [ Heelis et al ., ] is used to describe the high‐latitude forcing in the assimilation.…”

“…This brings up two main questions, (i) why the instability growth was suppressed over Taiwan, but favorable conditions existed over some other longitudes, such as the Indian sector, thus showing longitudinal differences in ionospheric response to the magnetic storm, and (ii) how, and if, the model could be improved to give realistic estimate of the EPB occurrence? 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.…”