Gang Lu

Effects of High-Latitude Input on Neutral Wind Structure and Forcing During the 17 March 2013 Storm

whawkins — Wed, 25 Sep 2024 20:35:09 +0000

Effects of High-Latitude Input on Neutral Wind Structure and Forcing During the 17 March 2013 Storm whawkins Wed, 09/25/2024 - 14:35

Author:

whawkins

Sep 25, 2024

Journal of Geophysical Research: This paper presents a quantitative assessment of the thermospheric forcing and its dependence on high-latitude driving is provided. Due to its coupling with the ionosphere via ion-neutral collisions, the simulated neutral wind and the corresponding thermospheric forcing from Global Circulation Models (GCMs) are highly dependent on the model's high-latitude ionospheric input. To study the effects of the different ionospheric inputs, we simulate the thermospheric winds using the Thermosphere-Ionosphere-Electrodynamics GCM (TIE-GCM) and compare them to the observed neutral wind vectors from the Scanning Doppler Imagers located in central Alaska during the St. Patrick’s Day storm in 2013. To assess the model-data discrepancies, the standard root-mean-square error (RMSE) is calculated, as well as the cross-correlation coefficient to better capture the structural differences between the simulated and observed winds. Additionally, individual thermospheric forces are analyzed, providing a full diagnosis of the relative importance of each force on the neutral wind behavior. It was found that the realistic high-latitude input resulted in better simulations of neutral wind structures than the empirical model did, although there was a slightly higher magnitude error. Altering the auroral energy flux mostly affected the resulting neutral wind speeds while the wind structures remained about the same. In the zonal direction, ion-drag is the dominant force, with significant contributions from the horizontal advection force and secondary contributions from the Coriolis and pressure-gradient forces. In the meridional direction, pressure-gradient is the dominant force, with secondary contributions from the ion-drag force and minor contributions from the Coriolis, horizontal advection and viscosity forces.

From top to bottom are (a and b) zonal and meridional neutral winds observed by the Poker Flat SDI, (b and f) modeled by Weimer driven and (c and g) by TIE-GCM driven simulations, (d and h) the latitudinal distribution of the root-mean-square error (RMSE) and the Pearson correlation coefficient of Weimer vs. SDI (solid lines) and AMIE vs. SDI (dashed lines).

Magnetosphere-ionosphere coupling via prescribed field-aligned current simulated by the TIEGCM

whawkins — Wed, 12 Oct 2022 19:22:26 +0000

Magnetosphere-ionosphere coupling via prescribed field-aligned current simulated by the TIEGCM whawkins Wed, 10/12/2022 - 13:22

Author:

whawkins

Oct 12, 2022

Hemispherically integrated Joule heating [GW] poleward of 50o magnetic latitude based on simulations with a prescibed empirical electric potential model: Weimer-POT (blue), with prescribed electric potential and auroral particle precipitation based on an assimilative method: AMIE-POT (black), and with prescribed field-aligned current: OIM-FAC (red) cases for the northern hemisphere (top) and southern hemisphere (bottom)

A. Maute, A.D. Richmond, G. Lu, D. Knipp, Y. Shi, B. Anderson assert that the magnetosphere-ionosphere (MI) coupling is crucial in modeling the thermosphere-ionosphere (TI) response to geomagnetic activity. In general circulation models (GCMs) the MI coupling is typically realized by specifying the ion convection and auroral particle precipitation patterns from e.g., empirical or assimilative models. Assimilative models have the advantage that the ion convection and auroral particle precipitation patterns are mutually consistent and based on available observations. However, assimilating a large set of diverse data requires expert knowledge and is time consuming. Empirical models, on the other hand, are convenient to use, but do not capture all the observed spatial and temporal variations. With the availability of AMPERE data, there is an opportunity for employing field-aligned currents (FAC) in numerical models to represent the MI coupling. In this study, we introduce a new method using observed FAC and solve for the interhemispherically asymmetric electric potential distribution. We compared geomagnetic storm simulations using the new approach and two other often-used methods for specifying MI coupling based on empirical and assimilative high latitude electric potentials. The comparison shows general similarities of the thermosphere-ionosphere storm time response and improved temporal variability of the new method compared to using empirical models, but results also illustrate substantial differences due to our uncertain knowledge about the MI coupling process.

Congratulations to Gang Lu, elected fellow of the AGU

kolinski — Mon, 22 Nov 2021 18:46:11 +0000

Congratulations to Gang Lu, elected fellow of the AGU kolinski Mon, 11/22/2021 - 11:46

Large-scale ionospheric disturbances during the 17 March 2015 storm: A model-data comparative study

kolinski — Thu, 18 Nov 2021 17:39:41 +0000

Large-scale ionospheric disturbances during the 17 March 2015 storm: A model-data comparative study kolinski Thu, 11/18/2021 - 10:39

Publication Name: JGR- Space Physics; First HAO Author's Name: Gang Lu

Author:

kolinski

Nov 18, 2021

Storm-induced ionospheric density variations are a major concern of near-Earth space environment as they could drastically disrupt satellite navigation and telecommunication systems. Although ionospheric disturbances such as traveling ionospheric disturbances (TIDs) and storm enhanced density (SED) are commonly observed during geomagnetic storms, accurate specification of these phenomena remains a great challenge for geospace models.

Large-scale ionospheric disturbances during the 17 March 2015 storm: A model-data comparative study.

This paper presents a detailed model-data comparative study of the well-known March 2015 St Patrick’s Day storm. The simulated TIDs and SED structures from the Thermosphere-Ionosphere-Electrodynamic General Circulation Model (TIEGCM) are compared with the total electron content (TEC) observations for a dense GNSS network over Europe, South and Central America, as well as North America. While the model reproduces many observed storm-related ionospheric features, quantitative differences between the simulation results and the GNSS data indicate that further improvements to the TIEGCM (such as a more realistic, self-consistent electrodynamic coupling of the ionosphere and magnetosphere) are required in order to meet the challenges of space weather specification, and eventually forecast. This study not only serves a meaningful validation of our numerical model but also shed some new lights on an apparent paradox concerning the formation of the SED plume.

Geospace response to an extreme solar flare

kolinski — Mon, 15 Nov 2021 21:58:00 +0000

Geospace response to an extreme solar flare kolinski Mon, 11/15/2021 - 14:58

Publication Name: AGU Advances; HAO Author: Jing Liu; Authors names as listed: Jing Liu, Wenbin Wang, Liying Qian, William Lotko, Alan G. Burns, Kevin Pham, Gang Lu, Stanley C. Solomon, et al.

Author:

kolinski

Nov 15, 2021

Solar flares—a sudden eruption of electromagnetic radiation at the Sun—are known to have significant impacts on Earth’s upper atmosphere and ionosphere, but their collective effects on geospace as an integrated system have never been examined. We use a newly developed whole geospace model, combined with key observational data, to study the effects of the 6 September 2017 X9.3 flare on the geospace system.

Solar flare effects on magnetospheric convection and ionospheric potential. Comparison of 50-minute averages (12:02-12:51 UT) from LTR simulations of magnetospheric and ionospheric states on September 6, 2017 with and without solar flare effects. Bottom row: LTR-simulated magnetospheric convection velocity in equatorial plane (ZGSM = 0) with (A) and without (B) solar flare effects and their difference (C). Arrows indicate direction and magnitude (also in color) of the convection velocity projected onto the plane. Top row: High-latitude electric potential, essentially convection streamlines in the ionosphere with (D) and without (E) solar flare effects and their difference (F). The minimum and maximum potentials are labeled below panels (D-F).

The analysis shows that the solar wind-magnetosphere interaction, magnetotail, field-aligned current distribution, auroral precipitation and high-latitude ionospheric convection respond to atmospheric absorption of solar flare radiation. This study, for the first time, demonstrates that a rapid and large increase in the iono-spheric E-region photoionization due to a solar transient event globally modifies the electrodynamic cou-pling of the geospace system.

Gang Lu

Effects of High-Latitude Input on Neutral Wind Structure and Forcing During the 17 March 2013 Storm

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Magnetosphere-ionosphere coupling via prescribed field-aligned current simulated by the TIEGCM

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Congratulations to Gang Lu, elected fellow of the AGU

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Large-scale ionospheric disturbances during the 17 March 2015 storm: A model-data comparative study

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Geospace response to an extreme solar flare

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