Art Richmond

New Expression of the Field-line Integrated Rayleigh-Taylor Instability Growth Rate

whawkins — Wed, 14 Feb 2024 15:42:27 +0000

New Expression of the Field-line Integrated Rayleigh-Taylor Instability Growth Rate whawkins Wed, 02/14/2024 - 08:42

Author:

whawkins

Feb 14, 2024

Seasonal and longitudinal variations of (a) R-T growth rate and (b) vertical ion drift during 2013 driven by observed solar and interplanetary parameters. The dashed lines represent the days when the solar terminator aligns with the magnetic field line.

Journal of Geophysical Research, Space Physics: An expression of Rayleigh-Taylor (R-T) instability growth rate based on the field-line integrated theory is newly established. This expression can be directly utilized in ionosphere models with magnetic flux tube structure based on Modified Apex Coordinates. In this study, the R-T instability growth rates are calculated using the thermospheric and ionospheric conditions based on the coupled Whole Atmosphere Model and Ionosphere Plasmasphere Electrodynamic model (WAM-IPE). The parameters used in this calculation include the field-line integrated conductivities and currents, which consider the Quasi-Dipole Coordinates and the modifications to the equations of electrodynamics. Detailed description of the new formulas and comprehensive analyses of diurnal, longitudinal, and seasonal variations of the R-T instability growth rate are carried out. The dependencies of growth rates on pre-reversal enhancement (PRE) vertical drifts and solar activity are also examined. The results show that pronounced R-T growth rates are captured between 18 and 22 local time (LT) when strong PRE occurs in the equatorial ionosphere. The simulated R-T growth rate increases with increasing solar activity levels and demonstrates strong correlations with the angle between the sunset terminator and the geomagnetic field line. These results are consistent with plasma irregularity occurrence rates shown in various satellite observations, suggesting that the newly developed R-T growth rate calculation can effectively capture the probability of irregularities by considering the changes along magnetic flux-tubes in the ionosphere. Since the WAM-IPE is running in operation at NOAA Space Weather Prediction Center (SWPC), the new calculations can be potentially implemented in the near future to provide forecasted information of the R-T growth rate.

Effect of Vertical Shear in the Zonal 1Wind on Low-Latitude Zonal Currents: An Observational Perspective Using Swarm and ICON Data

whawkins — Tue, 10 Jan 2023 23:59:46 +0000

Effect of Vertical Shear in the Zonal 1Wind on Low-Latitude Zonal Currents: An Observational Perspective Using Swarm and ICON Data whawkins Tue, 01/10/2023 - 16:59

Author:

whawkins

Jan 10, 2023

Journal of Geophysical Research: Space Physics: The winds in the ionosphere push the plasma in the presence of Earth's magnetic field, causing ions and electrons to move in different directions, producing electric current. The low-latitude ionospheric current system consists of an intense eastward current at the magnetic equator and off-equatorial reduced eastward or relative westward currents, which are called dip currents, in both hemispheres. Modelling studies have shown that the altitudinal gradient of the zonal wind is related to the strength of the dip currents. However, observational studies to validate these results have been missing to this date. This study utilizes simultaneous observations from ICON and Swarm satellites to provide insights on the connection between low-latitude winds and currents, which will improve our understanding of the causes of daytime ionospheric variability.

Quasi dipole latitudinal variations of the average Swarm and ICON conjunctions: EEJ from Swarm A (left), zonal wind from ICON/MIGHTI (middle), and the corresponding EEJ from the model (rihgt) showing that with westward turning winds in Pedersen conductivity dominated region (middle) the off-equatorial current dips are strong (left).

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.

Impacts of binning methods on high-latitude electrodynamic forcing: static vs boundary oriented binning methods

kolinski — Thu, 18 Nov 2021 18:45:53 +0000

Impacts of binning methods on high-latitude electrodynamic forcing: static vs boundary oriented binning methods kolinski Thu, 11/18/2021 - 11:45

Publication Name: JGR Space Physics; First HAO Author's Name: Art Richmond

Author:

kolinski

Nov 18, 2021

The Earth’s atmosphere is coupled at high latitude to the magnetosphere. This is a crucial region since energy is put into the upper atmosphere of Earth and is redistributed globally. Numerical models such as general circulation models (GCMs) simulate the effects of the high latitude energy input on the thermosphere-ionosphere system.

Distributions of height-integrated Joule heating in the northern hemisphere (geographic coordinates) from two GITM simulations for 2002 September 23 0010 UT: (a) Run 1 with static boundary binning and (b) Run 2 with boundary oriented binning. The hemispherically integrated Joule heating is given at the lower left of each plot. There is an 18% increase in integrated heating when employing the boundary oriented binning method.

However, an outstanding issue in the GCM simulations for Earth’s upper atmosphere is the inaccurate estimation of energy input, especially the Joule heating, which is associated with the inaccuracy of empirical models for high-latitude electrodynamic forcing. Several factors can contribute to the inaccuracy. In this study, we examine the influence of the binning methods used in the development of those empirical models on the Joule heating. Traditionally, data under similar conditions are binned through a static binning approach by using fixed geomagnetic coordinates, in which the dynamic nature of the forcing is not taken into account and therefore the forcing patterns may be significantly smoothed. To avoid the smoothing issue, data can be binned according to some physically important boundaries in the high-latitude forcing, i.e., through a boundary-oriented binning approach. In this study, we have investigated the sensitivity of high-latitude forcing patterns to the binning methods by applying both static and boundary-oriented binning approaches to the electron precipitation and electric potential data from the Defense Meteorological Satellite Program (DMSP) satellites. The forcing patterns obtained from both static and boundary-oriented binning approaches are used to drive Global Ionosphere and Thermosphere Model (GITM) to assess the impacts on Joule heating by using different binning patterns. It is found that the hemispheric-integrated Joule heating in the simulation driven by the boundary oriented binning patterns is 18% higher than that driven by the static binning patterns for southward IMF dominated case.

Modeling Diurnal Variation Magnetic Fields for Mantle Induction Studies

kolinski — Tue, 16 Nov 2021 21:21:54 +0000

Modeling Diurnal Variation Magnetic Fields for Mantle Induction Studies kolinski Tue, 11/16/2021 - 14:21

Publication Name: Geophysical Journal International; First HAO Author's Name: Astrid Maute; Authors: G.D. Egbert, P. Alken, A. Maute, H. Zhang, A.D. Richmond

Author:

kolinski

Nov 16, 2021

Accurate models of the spatial structure of ionospheric magnetic fields in the daily variation (DV) band (periods of approximately a few hours to a day) would enable use of magneto-variational methods for three-dimensional imaging of upper mantle and transition zone electrical conductivity. Constraints on conductivity at these depths, below what is typically possible with magnetotellurics, would in turn provide valuable constraints on mantle hydration and Earth’s deep water cycle. As a step towards this objective, we present here a novel approach to empirical modeling of global DV magnetic fields.

Magnetic Bx component[nT] at five representative sites for 9/20/2002 - 10/10/2002, the first half of this interval geomagnetic conditions were quiet (mean Kp 4) in the second half, with a significant storm (Kp = 7) on 10/01/2002. For each site we show the original observatory Bx time series (blue lines), the time domain PCA approximation using 20 modes for all bands (black lines), and global time domain model (red lines).

First, we apply frequency domain (FD) principal components analysis (PCA) to ground-based geomagnetic data to define the dominant spatial and temporal modes of source variability. Second, we apply FD PCA to gridded surface magnetic fields derived from outputs of the physics-based Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) to determine the dominant modes of spatial variability. Combining the two steps, we have a Frequency domain model of DV band global magnetic fields that is continuous in both space and time. The frequency domain model can easily be transformed back to the time domain (TD) to directly fit time-domain data. So far, the model uses only ground-based data, from 127 geomagnetic observatories. We show that the model accurately reproduces surface magnetic fields, including those at sites not used for model construction. Although fits are best during geomagnetically quiet times, and at mid-latitudes, the model tracks even complex magnetic field variations during storms, at all latitudes. Our preliminary model thus already represents an advance in empirical DV modeling.

Art Richmond

New Expression of the Field-line Integrated Rayleigh-Taylor Instability Growth Rate

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Effect of Vertical Shear in the Zonal 1Wind on Low-Latitude Zonal Currents: An Observational Perspective Using Swarm and ICON Data

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

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Impacts of binning methods on high-latitude electrodynamic forcing: static vs boundary oriented binning methods

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Modeling Diurnal Variation Magnetic Fields for Mantle Induction Studies

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