Science:

This effort will identify the extreme storm (Dst < -300 nT) dynamics that cause a co-rotating mid-latitude nighttime ionospheric localized density enhancement (NILE). During the extreme storms of solar cycle 23 a "hot spot" of 10 times as much total electron content (TEC) as the background nightside occurred within a span of only 500 km in the Gulf of Mexico region. The magnitude and localization of a NILE at midlatitudes adversely affects the availability of GNSS-based augmentation systems providing single-frequency user aircraft precision navigation service, e.g., the Wide Area Augmentation System (WAAS). No first principles ionospheric model predicts the existence of NILEs. Possible causes include an electrodynamic effect tied to the South Atlantic Anomaly or a super-fountain associated with interplanetary electric fields. This proposal will investigate events from solar cycles 23 and 24 to establish whether the phenomenon only occurs during extreme storms, determine whether such events are unique to the American sector, and test causal hypotheses by imaging the plasma density globally to estimate the drivers most consistent with the observations. 

Method:

The proposed work will combine advanced models with space-based data from NASA observatories along with ground-based measurements, all publicly available, to estimate the formation mechanism using the latest data assimilative techniques. The first principles model forming the a priori state will be SAMI3 (SAMI3 is Also a Model of the Ionosphere). Two data assimilative (DA) methods will subsequently ingest data to update the SAMI3 background: Ionospheric Data Assimilation 4-Dimensional (IDA4D) and Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE). We will use SAMI3, IDA4D, and EMPIRE to understand the physical processes consistent with the existence of a localized mid-latitude persistent nighttime plasma enhancement. SAMI3 has global fidelity in producing storm enhanced density, a possible precursor to the NILE. IDA4D will update the SAMI3 background model of plasma density with ground- and space-based density data, including from COSMIC, to produce a global time-varying specification of plasma densities. EMPIRE will update background models of electric potential and neutral winds based on electron density from IDA4D and measurements of the drivers from TIMED, DMSP, and C/NOFS. With these data covering the last two solar maxima, we will examine both extreme and not extreme storms. Space-based data are key to assimilation for dynamic driver estimation. DA lets us address the science goals because, while models do not yet predict the NILE itself, observationally driven updates offer optimal updates to the models, giving insight into the physics distinguishing NILE conditions from null events. 

FST Contributions: This proposal responds to Focused Science Topic 4: 

Understanding physical processes in the MITM system during extreme events. Global adjustments of first-principles electric potential based on observational stormtime conditions will indicate the states in which models most need adjustment during extreme storms. The study will help to show whether an extreme storm is a necessary condition for the NILE. This investigation will provide evidence of progress toward accurate simulation of extreme Space Weather events and their effects in the IT system by providing a rigorous uncertainty on the estimated state from DA. Output covariances and comparison to validation data provide metrics for determining the successful outcome of the research. We will contribute the electric field and neutral wind fields produced from SAMI3 and EMPIRE, and density specification from SAMI3 and IDA4D, to the FST. This effort will contribute insight into the low-to-mid-latitude electrodynamics during extreme storms, bringing a greater understanding of a phenomenon that has known consequences for the precision navigation availability of WAAS.