Identification of the temperature gradient instability as the source of decameter‐scale ionospheric irregularities on plasmapause field lines

Greenwald, R. A.; Oksavik, K.; Erickson, P. J.; Lind, Frank D.; Ruohoniemi, J. M.; Baker, J. B.; Gjerloev, J. W.

doi:10.1029/2006gl026581

Cited by 37 publications

(91 citation statements)

References 10 publications

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“…The Hokkaido radar was constructed in Rikubetsu town, Hokkaido, Japan at 43.53°N and 143.61°E in geographic coordinates. The magnetic latitude (MLAT) is 36.46°and the L-value is 1.55 (c.f., the Wallops radar [e.g., Greenwald et al, 2006] [4] The line-of-sight Doppler velocity observation of the flow reversal region is summarized in Figure 1. The spatial extent of the flow reversal region is about 1.5 hour in magnetic local time (MLT) and 5°in MLAT.…”

Section: Observational Resultsmentioning

confidence: 99%

“…This is just for discussing in the simplest way, based on the idea that the strong electric field and the density gradient near the edge of the subauroral trough may be effective in producing the field-aligned irregularities (FAIs). The production of FAIs in the subauroral region is an interesting and important topic [e.g., Greenwald et al, 2006], although detailed discussion on the FAI production itself is beyond the scope of this paper.…”

Section: Discussionmentioning

confidence: 99%

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Dynamic variations of a convection flow reversal in the subauroral postmidnight sector as seen by the SuperDARN Hokkaido HF radar

Kataoka¹,

Нишитани²,

Ebihara³

et al. 2007

Geophysical Research Letters

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The SuperDARN Hokkaido HF radar, capable of measuring the subauroral ionospheric plasma convection especially during storms, has been in continuous operation since the beginning of December 2006. We report the first two‐dimensional observation of a dynamic variation of convection flow reversal in subauroral postmidnight sector during the storm main phase on 29 January 2007. The flow reversal region is extended over 20° in longitude and 5° in latitude, lasting for about 10–15 min, and the maximum flow speed is about 0.5–1.0 km/s. The flow reversal structure is reasonably reproduced by the ring current simulation coupled with the ionosphere, suggesting that it is produced by the region 2 field‐aligned current associated with the ring current enhancement during the storm main phase. The dynamic variation of the flow reversal structure is interpreted as a transient eastward extension of the elongated dusk convection cell to the postmidnight and equatorward of the dawn cell, associated with the variation of the ring current whose structure is controlled by the interplanetary magnetic field and solar wind dynamic pressure. It is suggested that the ring current variation is highly coupled with the interplanetary parameters and is much more complicated than ever thought.

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Section: Observational Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Dynamic variations of a convection flow reversal in the subauroral postmidnight sector as seen by the SuperDARN Hokkaido HF radar

Kataoka¹,

Нишитани²,

Ebihara³

et al. 2007

Geophysical Research Letters

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“…Yizengaw and Moldwin [2005] showed that the equatorward wall of the midlatitude ionospheric trough is magnetically conjugate to the plasmapause, while the opposed temperature and density gradients are the precise conditions for the generation of F region TGI of Hudson and Kelley [1976]. Joint measurements by the Millstone Hill incoherent scatter radar (ISR) and the SuperDARN HF radar located at Wallops Island, Virginia, reported by Greenwald et al [2006] detected decameter-scale irregularities with low drift velocities (< 100 m/s) in the quiet time midlatitude nightside ionosphere. They showed that the irregularities are excited on the equatorward wall of the midlatitude ionospheric trough in a region of opposed density and temperature gradients.…”

Section: Figurementioning

confidence: 99%

“…Although the TGI is a form of universal instability, it can be damped by a conducting layer of the E region ionosphere that shorts out the electrostatic fields. Therefore, the TGI is only observed at night when the E region conductances have very low values [Greenwald et al, 2006].…”

Section: Figurementioning

confidence: 99%

Investigation of the temperature gradient instability as the source of midlatitude quiet time decameter‐scale ionospheric irregularities: 2. Linear analysis

et al. 2014

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Previous joint measurements by the Millstone Hill incoherent scatter radar and the Super Dual Auroral Radar Network (SuperDARN) HF radar located at Wallops Island, Virginia, have identified the presence of opposed meridional electron density and temperature gradients in the region of decameter‐scale electron density irregularities that have been proposed to be responsible for low‐velocity Sub‐Auroral Ionospheric Scatter observed by SuperDARN radars. The temperature gradient instability (TGI) and the gradient drift instability (GDI) have been extended into the kinetic regime appropriate for SuperDARN radar frequencies and investigated as the causes of these irregularities. A time series for the growth rate of both TGI and GDI has been developed for midlatitude ionospheric irregularities observed by SuperDARN Greenwald et al. (2006). The time series is computed for both perpendicular and meridional density and temperature gradients. This growth rate comparison shows that the TGI is the most likely generation mechanism for the irregularities observed during the experiment and the GDI is expected to play a relatively minor role in irregularity generation.

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“…Examples of cases when other methods are preferred include backscatter from midlatitude irregularities generated by the temperaturegradient instability (TGI) (Greenwald et al, 2006) and mixed scatter (Ponomarenko et al, 2008). In the most recent study on the issue, Ribeiro et al (2011) have employed the data from the midlatitude SuperDARN radar at Blackstone, Virginia to develop a new method for identifying TGI-generated scatter detected with midlatitude HF radars (defined in that study as being located at magnetic latitudes lower than 60 • ).…”

Section: Instrumentation and Data Post Processingmentioning

confidence: 99%

HF radar observations of ionospheric backscatter during geomagnetically quiet periods

2012

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Abstract. The quiet-time coherent backscatter from the Fregion observed by the Tasman International Geospace Environment Radar (TIGER) Bruny Island HF radar is analysed statistically in order to determine typical trends and controlling factors in the ionospheric echo occurrence. A comparison of the F-region peak density values from the IRI-2007 model and ionosonde measurements in the vicinity of the radar's footprint shows a very good agreement, particularly at subauroral and auroral latitudes, and model densities within the radar's footprint are used in the following analyses. The occurrence of F-region backscatter is shown to exhibit distinct diurnal, seasonal and solar cycle variations and these are compared with model trends in the F-region peak electron density and Pedersen conductance of the underlying ionosphere. The solar cycle effects in occurrence are demonstrated to be strong and more complex than a simple proportionality on a year-to-year basis. The diurnal and seasonal effects are strongly coupled to each other, with diurnal trends exhibiting a systematic gradual variation from month to month that can be explained when both electron density and conductance trends are considered. During the night, the echo occurrence is suggested to be controlled directly by the density conditions, with a direct proportionality observed between the occurrence and peak electron density. During the day, the echo occurrence appears to be controlled by both conductance and propagation conditions. It is shown that the range of echo occurrence values is smaller for larger conductances and that the electron density determines what value the echo occurrence takes in that range. These results suggest that the irregularity production rates are significantly reduced by the highly conducting E layer during the day while F-region density effects dominate during the night.

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Identification of the temperature gradient instability as the source of decameter‐scale ionospheric irregularities on plasmapause field lines

Cited by 37 publications

References 10 publications

Dynamic variations of a convection flow reversal in the subauroral postmidnight sector as seen by the SuperDARN Hokkaido HF radar

Dynamic variations of a convection flow reversal in the subauroral postmidnight sector as seen by the SuperDARN Hokkaido HF radar

Investigation of the temperature gradient instability as the source of midlatitude quiet time decameter‐scale ionospheric irregularities: 2. Linear analysis

HF radar observations of ionospheric backscatter during geomagnetically quiet periods

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