Observations and modeling of the April 10–12, 1997 ionospheric storm at Millstone Hill

Schlesier, A.; Buonsanto, M. J.

doi:10.1029/1999gl900486

Cited by 15 publications

(12 citation statements)

References 12 publications

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“…In fact, observations have indicated that vertical gradients of the horizontal winds exist in the upper thermosphere. Vertical shears in horizontal wind profiles were observed in the upper thermosphere at lower latitudes by Burnside et al [1983, 1991] and by Schlesier and Buonsanto [1999a, 1999b] at middle latitudes. Gravity waves are also known to produce neutral wind shears in the upper thermosphere [ Richmond and Matsushita , 1975; Millward et al , 1993].…”

Section: Introductionmentioning

confidence: 93%

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

et al. 2008

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[1] It is generally assumed that viscosity smooths out vertical gradients of the horizontal thermospheric winds in the upper thermosphere, and thus observations of neutral winds at one height can be used at other altitudes in this region. In this paper we present neutral wind simulations of the May 1997 geomagnetic storm using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The model results show that during quiet periods, the assumption of a shearless vertical profile of the horizontal winds is generally valid in low and middle latitudes, although vertical shears do occur in wind profiles in the upper thermosphere in some locations at higher latitudes. During disturbed periods, large variations in the vertical profiles of the upper thermospheric winds are seen globally in the model simulations. A diagnostic analysis of the forcing processes in the neutral momentum equations shows that (1) during quiet time, there are shearing forces, most noticeably the pressure gradient and ion drag, in the upper thermosphere that result in a net momentum forcing that changes with height; this induces altitude variations in the wind profiles at high latitudes and sometime even at middle latitudes. (2) During storm time, momentum advection, which is relatively weak during the quiet time, becomes a dominant force globally. Pressure gradient forces are also significantly enhanced. Ion drag, on the other hand, can be enhanced or suppressed, depending on the location of positive or negative effects. All these forces exhibit significant altitude variations that lead to a net force that is greatly enhanced and has large vertical shears. This produces globally enhanced neutral winds that vary with height. (3) Viscosity is less important than other forcing processes during both the quiet and storm periods and thus cannot prevent shears from occurring in the vertical profiles of the horizontal winds. Viscosity has an insignificant effect on vertical shears that change with height linearly. It, however, does restrict vertical shears that vary nonlinearly with height. The effectiveness of the viscosity in restricting such shears depends on its magnitude. In our simulations, viscosity is weaker than other forcing processes and thus is a relatively slow process, so it will take a few hours for viscosity to reduce such shears.

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Section: Introductionmentioning

confidence: 93%

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

et al. 2008

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“…Buonsanto (1995) reports a strong altitude variation in vertical ion drift in the evening hours over Millstone Hill during a positive storm phase. The altitude variation in the meridional wind was predicted in the modeling effort by Schlesier and Buonsanto (1999), who found that inclusion of a vertical gradient in the neutral wind produces better data/model agreement. Large vertical gradient in the neutral wind was interpreted by Schlesier and Buonsanto (1999) as a result of TAD.…”

Section: Article In Pressmentioning

confidence: 99%

“…The altitude variation in the meridional wind was predicted in the modeling effort by Schlesier and Buonsanto (1999), who found that inclusion of a vertical gradient in the neutral wind produces better data/model agreement. Large vertical gradient in the neutral wind was interpreted by Schlesier and Buonsanto (1999) as a result of TAD. The characteristics of a wind shear were found to be in agreement with TAD simulations by Millward et al (1993b).…”

Section: Article In Pressmentioning

confidence: 99%

Observations of a positive storm phase on September 10, 2005

Гончаренко

Foster

Coster

et al. 2007

Journal of Atmospheric and Solar-Terrestrial Physics

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“…Pavlov and Buonsanto (1998), Pavlov (1998), Pavlov et al (1999), Schlesier and Buonsanto (1999), and Pavlov and Foster (2001) studied the G condition formation for quiet and disturbed mid-latitude ionosphere during periods of low, moderate, and high solar activity, using the Millstone Hill incoherent scatter radar data. Model results also show that O + can become a minor ion in the F-region, creating a G condition during disturbed conditions at high latitudes (Banks et al, 1974;Schunk et al, 1975), and observations at EIS-CAT confirm this conclusion (e.g.…”

Section: Introductionmentioning

confidence: 99%

Solar zenith angle dependencies of F1-layer, <i>Nm</i>F2 negative disturbance, and G-condition occurrence probabilities

Lobzin

Павлов

2002

Ann. Geophys.

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Abstract. Experimental data acquired by the Ionospheric Digital Database of the National Geophysical Data Center, Boulder, Colorado, from 1957, are used to study the dependence of the G condition, F1-layer, and NmF2 negative disturbance occurrence probabilities on the solar zenith angle during summer, winter, spring, and autumn months in latitude range 1 (between −10 • and +10 • of the geomagnetic latitude, ), in latitude range 2 (10, and in latitude range 5 (60 • < | | ≤ 90 • ), where ϕ is the geographic latitude. Our calculations show that the G condition is more likely to occur during the first half of a day than during the second half of a day, at all latitudes during all seasons for the same value of the solar zenith angle. The F1-layer occurrence probability is larger in the first half of a day in comparison with that in the second half of a day for the same value of the solar zenith angle in latitude range 1 for all seasons, while the F1-layer occurrence probability is approximately the same for the same solar zenith angle before and after noon in latitude ranges 4 and 5. The F1-layer and G condition are more commonly formed near midday than close to post sunrise or pre-sunset. The chance that the daytime F1-layer and G condition will be formed is greater in summer than in winter at the given solar zenith angle in latitude ranges 2-5, while the F1-layer occurrence probability is greater in winter than in summer for any solar zenith angle in latitude range 1. The calculated occurrence probability of the NmF2 weak negative disturbances reaches its maximum and minimum values during daytime and night-time conditions, respectively, and the average night-time value of this probability is less than that by day for all seasons in all studied latitude regions. It is shown that the NmF2 normal, strong, and very strong negative disturbances are more frequent on average at night than by day in latitude ranges 1 and 2 for all seasons, reaching their maximum and minimum occurrence probability values at night and by day, respecCorrespondence to: A. V. Pavlov (pavlov@izmiran.rssi.ru) tively. This conclusion is also correct for all other studied latitude regions during winter months, except for the NmF2 normal and strong negative disturbances in latitude range 5. A difference in the dependence of the strong and very strong NmF2 negative disturbance percentage occurrences on the solar zenith angle is found between latitude ranges 1 and 2. Our results provide evidence that the daytime dependence of the G condition occurrence probability on the solar zenith angle is determined mainly by the dependence of the F1-layer occurrence probability on the solar zenith angle in the studied latitude regions for winter months, in latitude range 2 for all seasons, and in latitude ranges 4 and 5 for spring, summer, and autumn months. The solar zenith angle trend in the probability of the G condition occurrence in latitude range 3 arises in the main from the solar zenith angle trend in the F1-layer occurrence probability. The solar zenith ...

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Observations and modeling of the April 10–12, 1997 ionospheric storm at Millstone Hill

Cited by 15 publications

References 12 publications

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

Observations of a positive storm phase on September 10, 2005

Solar zenith angle dependencies of F1-layer, <i>Nm</i>F2 negative disturbance, and G-condition occurrence probabilities

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Observations and modeling of the April 10–12, 1997 ionospheric storm at Millstone Hill

Cited by 15 publications

References 12 publications

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

Altitude variations of the horizontal thermospheric winds during geomagnetic storms

Observations of a positive storm phase on September 10, 2005

Solar zenith angle dependencies of F1-layer, &lt;i&gt;Nm&lt;/i&gt;F2 negative disturbance, and G-condition occurrence probabilities

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Solar zenith angle dependencies of F1-layer, <i>Nm</i>F2 negative disturbance, and G-condition occurrence probabilities