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Ground Magnetic Disturbances (GMD) due to Neutral-wind Driven Ionospheric Currents

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Cheng Sheng¹, Yue Deng¹, Daniel T. Welling^1,2, and Steven K. Morley³

¹UTA ²UMich ³LANL

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AGU Fall Meeting 2022

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• Major sources for ground magnetic disturbances (dB)
• J_Mag, J_Gap, J_Hall, J_Peder

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• What can GCMs, such as GITM, provide?
• Ionospheric Currents: no assumptions & 3-dimentional
• Neutral-wind-driven Currents: On the average, the wind-driven FACs amount to 27% of the total FACs [Lu et al., 1995].

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I. Background & Motivation

Welling [2019]

Marsal et al. [2012]

Jp_Total

Jp_EField

Jp_UCrossB

• 5-hour simulation; Equinox condition and F10.7=150 s.f.u.
• Using step functions for IMF and SW conditions when transitioning
• IMF B_Z = 0 nT (Quiet) 🡪 -20 nT (Active) 🡪 0 nT (Reovery)
• SW V = 400 km/s (Quiet) 🡪 800 km/s (Active) 🡪 400 km/s (Recovery)
• SW N = 3.74 /cc (Quiet) 🡪 4.67 /cc (Active) 🡪 3.74 /cc (Recovery)

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• Questions:
• Neutral wind contribution to FACs
• Neutral wind contribution to dB

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II. An Idealized Event

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III. Geomagnetic Forcing

• Electron energy flux, specified by Fuller-Rowell and Evans [1987]
• Hemispheric power increases from 21.1 to 136.3 GW from Quiet to Active time.

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III. Geomagnetic Forcing

• FACs = Divergence of horizontal ionospheric currents
• FACs are dominated by the external electric field when the external electric field presents.
• FACs due to neutral winds are usually anti-sign with those due to the external electric field. Neutral winds contribute to ~25% of the total FACs.
• During the recovery time and at middle latitudes (the external electric field is absent), FACs are driven by neutral winds.

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IV. FACs

Quiet

Active

Recovery

±1

±2

±1

• Slow neutral wind recovery 🡪 FACs at middle latitudes on the dayside (large conductivity) during the recovery phase
• Left: Zonal winds at 110 km
• Right: Height-integrated horizontal ionospheric currents in the meridional direction

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IV. Neutral Wind Recovery

• Maximum dBNorth increases by ~10 times from Quiet to Active times.
• dB due to the external electric field is much larger than those due to neutral winds.
• dB driven by neutral winds during the active time is about the same magnitude as dB due to the external electric field during the quiet time.
• dB due to neutral winds is usually anti-sign with dB due to the external electric field.
• Neutral-wind-driven currents at middle latitudes on the dayside during the recovery time 🡪 Dominant source of dB at those locations

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IV. dBNorth

Quiet

Active

Recovery

±100

±1000

±100

• Neutral-wind-driven currents contribute to ~10-20% of the total currents and dB when the external electric presents.
• During the recovery phase, neutral wind is the dominant driver for FACs and dB at middle latitudes on the dayside.

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• What and how do ionospheric and thermospheric processes contribute to GMD and GIC in real events?

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Summary and Question

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Backup Slides

• On the average, the wind-driven FACs amount to 27% of the total FACs.

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I. Background & Motivation

Lu et al. [1995]

• Selected events from the matrix
• R00 🡪 R10, IMF change; R10 🡪 R20, SW changes.
• Particle model (Fuller-Rowell and Evans [1987]) saturates during the active time of R10. R10 🡪 R20, only ion convection (Weimer05) gets enhanced.

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II. Idealized Events

• At 225°E Longitude, 1500 LT at 0000 UT

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V. R20, dBNorth At a Fixed Longitude

• Steady forcing 🡪 “Steady” dB/dt
• Neutral-wind-driven currents contribute to ~10-20% of the total dB when external electric fields present.
• During the recovery phase, neutral-wind-driven current is the dominant source of dB at middle latitudes on the dayside.

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V. R20, dBNorth At a Fixed Longitude

• From R10 to R20, CPCP increases, and the potential pattern expands to lower latitudes.
• On the afternoon-dusk side, R10 produces larger currents and dB in a narrower region.

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V. R10 vs. R20