LISN Model/Data Inversion to Determine the Drivers of the Low-Latitude Ionosphere (Comparisons with JRO ISR Drift Measurements) Vince Eccles (Modeling) Space Environment Corporation, Providence, Utah Erhan Kudeki (JRO ISR) University of Illinois Cesar Valladares (LISN) Boston College

Assimilation of Ionospheric Data for the Low-Latitude Ionosphere Ionospheric model-data assimilation methods typically modify electron density specifications to best match TEC observations. – 3D ionospheric density specification. Ensemble physics-based ionospheric model-data assimilation modifies the vertical plasma drift and meridional F region neutral wind to produced an ensemble of ionospheric specifications for model-data inversion to reproduce TEC observations. – 3D ionospheric density specification. – Vertical plasma drift and meridional F region wind. Ensemble physics-based ionosphere & electric field model modifies a 3D neutral wind description to produce an ensemble of ionospheric specifications for model-data inversion to reproduce observations. – 3D ionospheric density specification. – Vertical and horizontal plasma drifts – 3D neutral wind. – Penetration electric fields

Physics-based Model-Data Inversion for the LISN Region The LISN Model-Data inversion uses a self-consistent physics-based ionosphere & electric field model and a full neutral wind description to produce an ensemble of results for model-data inversion. – LLIONS: Low-Latitude Ionospheric Sector Model – SEF: Simple Electric Field Model – Tidal description of Neutral Winds E region tides – Solar diurnal, semi-diurnal(phase, magnitude) – Lunar semi-diurnal (phase, magnitude) F region winds – My own secret recipe for zonal winds. (HWM07 sort of) – Meridional F region winds are tidal extensions of the E region with ad hoc additions as assimilation requires.

Physics-based Models: LLIONS Single magnetic meridian model based on the low-latitude portion of the Ionospheric Forecast Model (IFM). Solves for H +, O +, NO +, O 2 +, and e - densities based on solar spectrum, neutral density, neutral winds, & vertical plasma drift.

Physics-based Models: SEF Single magnetic meridian electric field model based on a global electric field model using field-line-integrated physics. Solves for zonal and vertical electric fields (ExB plasma drifts) based on conductivities and neutral winds in the magnetic meridian sector (it approx. reproduces the global model results)

LLIONS-SEF Model Scherliess & Fejer vertical drift model and zonal drifts from Fejer. LLIONS-SEF with HWM 2007 LLIONS-SEF with best tides and F region winds

Methodology

Public Access to Physics-Based Processing of LISN Data Results to be placed at LISN data center. Near real-time processing by end of project.

LISN Model-Data Study Fall 2009 Period Model/data study with LISN instruments – Magnetometers (electric fields) – VIPIR (F peak height & density) September-October used for the determination of neutral wind drivers – Electric fields & ionosphere distribution being self-consistent with the neutral wind fields

VIPER and Magnetometer Data Observed in Peruvian Sector (Lunar Tides?)

Solar & Lunar Driven Tides on Vertical Plasma Drift

Neutral Winds Definition for Fall Used magnetometer and VIPIR observations to optimally determine tides. 2.Thermal-driven tide definition from October data. -Solar diurnal tide: (1,-2) Hough mode 3.Gravitational-driven tides definition from Fall data. – Solar semi-diurnal tide: (2,2) Hough mode – Lunar Semi-diurnal tide: (2,2) Hough mode

Model Results Scherliess & FejerSimple Electric Field VIPIR

Does the single definition work for the whole LISN Region?

Modeling Lunar Tides

Conclusions for Fall 2009 Study Single diurnal solar tide with single definition for Solar and Lunar semi-diurnal tides provide a reasonable neutral wind driver definition to drive the low-latitude ionosphere/electric field model for the September through November – Solar diurnal (1,-2) tide with 130 m/s magnitude with static phase. – Semi-diurnal (2,2) for both solar and lunar with identical magnitude (65 m/s) with a static phase definition for each. Departures are assumed to be high-latitude inputs and/or tropospheric weather inputs into the neutral winds.

LISN Model-Data Inversion Goal is to identify the drivers of ionosphere- electric fields in the LISN region. – Neutral wind specification is determined using an ensemble of model runs, then use data and sim- data to determine the optimal tidal definition. – The data-model inverstion is performed over two time scale epochs of 2 months and 1 day to obtain the periodic wind structure and the aperiod wind structure, respectively

2 Time Scales - Assimilation Two time scales 2 months data used to determine current epoch drivers – Solar & Lunar gravitationally-driven semi-diurnal tides. – Solar thermal diurnal tide. – Adjustments to meridional F region wind (from Hough mode) 1 day data used to examine departures from long time scale driver definition – Penetration electric fields – Aperiodic winds (tropospheric weather & storm dynamo winds) Benefit of this approach identifies specific sources for the neutral wind structure. Rather than just the 3D neutral wind structure.

Test Winter/Spring 2009 Jicamarca Radar ISR observations available to test assimilation results (January 2009). GPS-TEC and magnetometer data used for Peruvian sector for winter/spring Same solar & lunar tidal structure?

LISN TEC for Peruvian Sector Jan 1-15, 2009

Jicamarca Radar Data Required The assimilation of TEC was unsuccessful. – “Best” match required zero wind velocities. – The observed very low TEC values could not be matched. The LLIONS results do not match ionosphere observations during very low solar conditions – Needed to stepping back from assimilation to examine ionization model of LLIONS – Used the Jicamarca vertical drifts to reduce unknowns.

LLIONS Model Reexamination Jicamarca Radar Observatory 2009 Jan 9-13 These data are reduced to provide Vertical drifts and zonal drifts for LLIONS.

Required LLIONS Correction The LLIONS ionization determination requires a secondary photo electron component. This component was too large for the very low solar conditions of This was adjusted to produce the observed TEC values given the vertical plasma drifts observed by Jicamarca radar.

JRO drifts & Best Tide Definition Smaller (than Fall value) gravitational tide magnitude (30 m/s). Smaller thermal tide magnitude (80 m/s) Same phases as previous study of Fall 2009

Comparison to Magnetometer Obs A small amplitude 4 rd tidal mode reveals itself during the lunar phase where the solar and lunar gravitational tides cancel each other (5 th -8 th ). When the lunar and solar gravitational tides constructively superimpose, then the 4 th tidal mode is not apparent (10 th -16 th ).

LLIONS Adjustments for Very Low Solar Conditions The neutral wind tides that best matched the Jicamarca Observations were used in LLISN-SEF with the new photo electron parameterization. GPS-VTEC predictions are now approximately correct. Meridional F region wind adjustment is the remaining important adjustment for the assimilation.

Current Situation of LISN Model/Data Inversion The LLIONS model better matches the observe TEC for very low conditions. – The lunar tidal component is smaller than determined in the Fall 2009 study. Correction? – F region North-South wind modification will be obtained for long scale assimilation. – Finally, perform aperiod 1-day assimilation.

Summary The LISN model-data assimilation is performed to determine regular and aperiodic drivers of the low-latitude ionosphere. Doing this at two difference time-scales creates additional insight into the component drivers of the neutral wind. There is a possibility that a single tidal description of thermal (F10.7 dependence) and gravitational tides may capture most of the quiet time variations of ionospheric weather.