Magnetic Shear Damped Polar Convective Fluid Instabilities

Atul, J.K.; Singh, Rameswar; Sarkar, Samrat; Kravchenko, O. V.; Singh, Sushil K.; Chattopadhyaya, P. K.; Kaw, P. K.

doi:10.1002/2017ja024778

Cited by 4 publications

(8 citation statements)

References 60 publications

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“…The plasma convection in this study is simplified as the high‐latitude horizontal

\overset{E}{true} \times \overset{B}{true}

drift by ignoring other contributions to drift. However, to examine LCSs globally, a study would need to be conducted with modeled plasma drifts including electric Pedersen drift, gravitational Pedersen drift, pure gravitational drift, and parallel mean flow (Atul et al, ; Sotnikov et al, ). This would likely lead to a three‐dimensional flow field, requiring 3‐D LCS analysis, which ITALCS does not currently treat.…”

Section: Discussionmentioning

confidence: 99%

“…For this analysis, the flow of interest is the plasma drift convection as a flow field at high latitudes in both hemispheres. While in general plasma drift is a superposition of electric Pedersen drift, gravitational Pedersen drift, pure gravitational drift, and parallel mean flow (Atul et al, ; Sotnikov et al, ), in the high‐latitude region above 50° geomagnetic latitude, the plasma drift is dominated by

\overset{E}{true} \times \overset{B}{true}

drift due to the absence of vertical shears (Anderson et al, ; Kirchengast, ). The

\overset{E}{true} \times \overset{B}{true}

drift is governed by the local electric and magnetic fields:

{\overset{v}{true}}_{E \times B} = \frac{- \overset{\nabla}{true} V \times \overset{B}{true}}{B^{2}}

where V is an electrostatic potential function and

\overset{B}{true}

is the magnetic field.…”

Section: Introductionmentioning

confidence: 99%

“…The mechanism for scintillation is electromagnetic wave scattering due to variations in density (Sotnikov et al, 2014). Polar cap patch scintillations are believed to arise due to a number of possible instability mechanisms (Atul et al, 2018;Burston et al, 2016;Moen et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Horseshoes in the High‐Latitude Ionosphere

et al. 2018

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In the high‐latitude ionosphere, predicting transport of polar cap patches is important because of their impact on radio communications and navigation systems. Lagrangian coherent structures (LCSs) are barriers to transport in nonlinear time‐varying flow fields, found by computing the local maximum finite‐time Lyapunov exponent (FTLE). We propose that LCSs are barriers governing patch formation. In this work, we compute and visualize the LCSs in high‐latitude ionospheric convection by computing the FTLE field with the Ionosphere‐Thermosphere Algorithm for Lagrangian Coherent Structures (ITALCS). The Weimer 2005 high‐latitude electric potential model and the 12th‐generation International Geomagnetic Reference Field (IGRF‐12) are used to generate the trueE→×trueB→ drift field at each gridpoint in the ionosphere. The trueE→×trueB→ drifts are used as the input to ITALCS. Time‐varying structures are detected in two‐dimensional ionospheric drifts at high latitudes based on locally maximum forward time FTLE values for both geomagnetically stormy and quiet periods. Typically, the dominant structure is shaped like the letter “U,” or a “horseshoe,” oriented with the curved portion of the “U” on the dayside around local noon. The LCSs during the geomagnetically stormy period have more complex topology and shift equatorward compared to the LCSs during quiet times. Analysis of a polar cap patch observed on 17 March 2015 with the Multi‐Instrument Data Analysis System indicates that a necessary condition for its formation and transport is that storm enhanced density exist poleward of the LCS.

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“…The plasma convection in this study is simplified as the high‐latitude horizontal

\overset{E}{true} \times \overset{B}{true}

Section: Discussionmentioning

confidence: 99%

\overset{E}{true} \times \overset{B}{true}

drift due to the absence of vertical shears (Anderson et al, ; Kirchengast, ). The

\overset{E}{true} \times \overset{B}{true}

drift is governed by the local electric and magnetic fields:

{\overset{v}{true}}_{E \times B} = \frac{- \overset{\nabla}{true} V \times \overset{B}{true}}{B^{2}}

where V is an electrostatic potential function and

\overset{B}{true}

is the magnetic field.…”

Section: Introductionmentioning

confidence: 99%

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Horseshoes in the High‐Latitude Ionosphere

et al. 2018

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“…Scintillation can degrade the performance of the Global Navigation Satellite System (GNSS) by causing loss of satellite lock and may lead to positioning errors (Moen et al, ; Pi et al, ). Previous work has proposed that polar cap patches may lead to scintillation through one or more of the following instability mechanisms: gradient drift, current convective, and Kelvin‐Helmholtz instabilities, as well as small‐scale “turbulence" processes (Atul et al, ; Burston et al, ; Moen et al, ). Because of this, it is important to study the formation and propagation of polar cap patches.…”

Section: Introductionmentioning

confidence: 99%

“…In general, plasma motion has components parallel and perpendicular to the local magnetic field. The motion is the sum of the electric Pedersen drift, gravitational Pedersen drift, pure gravitation drift, and parallel mean flow (Atul et al, ; Sotnikov et al, ). Specifically, in the high‐latitude ionosphere, plasma motion is coupled to the magnetosphere and the IMF.…”

Section: Introductionmentioning

confidence: 99%

SuperDARN Evidence for Convection‐Driven Lagrangian Coherent Structures in the Polar Ionosphere

et al. 2019

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Polar cap patches are large sporadic enhancements of plasma density on the scale of hundreds of kilometers, which can impact the performance of Global Navigation Satellite Systems. Lagrangian Coherent Structures (LCSs) are ridges that show areas of maximal separation in a time‐evolving flow. Previous work based on modeled ionospheric flow showed that LCSs exist in the ionosphere and are barriers governing patch formation. In this work, we identify the first data‐driven LCSs in the high‐latitude ionosphere using Super Dual Auroral Radar Network (SuperDARN) ion convection fields. The LCSs found using the Ionosphere‐Thermosphere Algorithm for LCSs are compared during geomagnetically quiet and active periods. The shape of the LCS is found to be dependent on the electric potential pattern. A consistent two‐cell pattern results in a W‐shaped LCS, but when the two‐cell pattern breaks down, the LCS loses this characteristic shape. The changes in the electric potential, and thus the LCS, are likely due to changes in the interplanetary magnetic field. A comparison between LCSs obtained from empirical models and data reveal that the data‐driven LCSs are poleward of and have a shorter longitudinal span than the model‐based LCSs. A comparison of the LCS location and the formation of a polar cap patch on 17 March 2015 showed that the center of the patch developed from plasma on the main LCS ridge, and this is confirmed with a separate polar cap patch event from 26 September 2011.

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Statistics of Traveling Ionospheric Disturbances at High Latitudes Using a Rapid‐Run Ionosonde

Moges,

Sherstyukov,

Kozlovsky

et al. 2024

JGR Space Physics

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The potential of deep learning for the investigation of medium scale traveling ionospheric disturbances (MSTIDs) has been exploited through the Sodankylä rapid‐run ionosonde in this statistical study. The complementing observations of the Sodankylä ionosonde with those of the Sodankylä meteor radar reveals the diurnal and seasonal occurrence rate of high‐latitude MSTIDs in the recent low solar activity period, 2018–2020. In our results, the daytime, nighttime and dusk MSTIDs are predominantly identified during winter, summer, and equinoctial months, respectively. The winter daytime higher (lower) occurrence rate is well correlated with the lower (higher) altitude of the height of the F2‐layer peak (hmF2), and the low occurrence rate of the summer daytime is well correlated with the mesosphere‐lower‐thermosphere wind shear and higher gradient of temperature. Relatively high occurrence rate (>0.4) of summer nighttime MSTIDs has a general—but not one‐to‐one agreement—with post‐noon to evening IU (eastward auroral current index) inferred ionospheric conductivity. Rather, we see a one‐to‐one relationship between the summer nighttime MSTIDs and zonal wind shear suggesting that the wind shear‐induced electrodynamic processes could play significant roles for higher occurrence rate of MSTIDs. Furthermore, significant MSTIDs with ∼0.4 occurrence rate are so far revealed during spring and autumn transition periods. The enhanced nighttime MSTID amplitudes during the equinox are observed to be well correlated with IL index (westward auroral current indicator) suggesting that the particle precipitation during substorms could be the primary cause.

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Magnetic Shear Damped Polar Convective Fluid Instabilities

Cited by 4 publications

References 60 publications

Horseshoes in the High‐Latitude Ionosphere

Horseshoes in the High‐Latitude Ionosphere

SuperDARN Evidence for Convection‐Driven Lagrangian Coherent Structures in the Polar Ionosphere

Statistics of Traveling Ionospheric Disturbances at High Latitudes Using a Rapid‐Run Ionosonde

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