Seasonal and solar cycle variations in the thermospheric circulation observed over Millstone Hill

Babcock, R. R.; Evans, J. V.

doi:10.1029/ja084ia12p07348

Cited by 27 publications

(15 citation statements)

References 18 publications

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“…The diurnally averaged meridional winds tend to be more equatorward on very disturbed days, but again the pattern is not consistent. In analyzing 64 quiet days (daily average of AE < 300 3') over a 6-year period [Babcock and Evans, 1979 While the trend is for the winds to be more equatorward on disturbed days, the scatter is so large that the result is not significant statistically.…”

Section: Resultsmentioning

confidence: 98%

“…However, during disturbed periods, we find that the zonal winds calculated in this manner become much larger than normal and the non-linear terms may no longer be unimportant. Three variations to the analysis procedures employed previously for quiet days [Babcock and Evans, 1979] were included in this analysis. Since the derived neutral winds were found to be significantly larger than during quiet times, the contribution of frictional heating, caused by ion-neutral collisions to the heat balance equation was included in the derivation of T•,; this tended to reduce the values of T•, derived.…”

Section: Introductionmentioning

confidence: 99%

“…It has been established that the increase in exospheric temperature over Millstone as a function of the Ap index is much more pronounced in summer than winter. It seems likely that this arises because there is more intense Joule heat-The difference between average meridional velocity (P) and that predicted (I/FIT) from a model fitted to the 64 quiet days analyzed byBabcock and Evans [1979] plotted against the daily average auroral index/IE. The straight line is the least mean square fit.…”

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confidence: 99%

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Effects of geomagnetic disturbances on neutral winds and temperatures in the thermosphere observed over Millstone Hill

Babcock¹,

Evans²

1979

J. Geophys. Res.

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Ionospheric measurements of electron density, electron and ion temperature, and vertical drift made at the Millstone Hill incoherent scatter radar have been used to derive the neutral exospheric temperature and the thermospheric neutral wind speed along the magnetic meridian. These two parameters were used as input to a dynamic model for the neutral atmosphere over Millstone from which values of the zonal and meridional winds at 300 km were derived. Of 85 days of data available over the 6 year period 1970‐1975, 21 days were geomagnetically active (daily average AE ≥ 300 γ). In analyzing the disturbed days, heating of the ions by the neutral winds, differences in the neutral density from MSIS model predictions, and electric field effects were taken into consideration. All disturbed days show three distinct effects, viz., enhanced nighttime temperatures, strong equatorward nighttime winds, and transition of the zonal winds from eastward to westward much earlier in the nighttime sector than usual. The strong equatorward winds transport high latitude heat away from the auroral zone. They usually are found to maximize after midnight and probably represent an extension to mid‐latitudes of the ‘midnight surge’ seen at auroral latitudes (Bates and Roberts, 1977). In the daytime sector, some disturbed days exhibit poleward winds, which are not as strong as normal, but this does not seem to be a consistent feature.

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Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Effects of geomagnetic disturbances on neutral winds and temperatures in the thermosphere observed over Millstone Hill

Babcock¹,

Evans²

1979

J. Geophys. Res.

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“…Fuller-Rowell et al, 1996;Field et al, 1998;Richmond and Lu, 2000 transport of neutral composition changes to lower latitudes. The resulting equatorward wind is stronger at night, because the additional geomagnetic storm equatorward wind is added to the quiet day-to-night circulation and because the additional wind is reinforced by antisunward ion drag due to magnetospheric convection E×B drifts (Straus and Schulz, 1976;Babcock and Evans, 1979). As a result, the neutral composition disturbance zone reaches more lower latitudes at night than by day, and the NmF2 normal, strong and very strong negative disturbances tend to be more frequent on average at night than by day in latitude ranges 1 and 2 for all seasons (see Figs.…”

Section: Nmf2 Normal Strong and Very Strong Negative Disturbance Occmentioning

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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“…These studies have shown that during the solstice period a summer-towinter mean meridional wind exists, but the circulation reverses in the winter F region if significant Joule heating is present at high latitudes. The conclusions of these models have been largely confirmed by the measurements of meridional winds deduced from observations of the 630.0-nm airglow Doppler shift [Hernandez and Robie, 1976a, b] and by incoherent scatter radar measurements [Emery, 1978a, b; Babcock and Evans, 1979;OliVer, 1980]. The coupling between zonal mean dynamics and composition in the lower thermosphere was studied by Kasting and Robie [1981] and Robie and Kasting [this issue], and their results are used as background properties for our calculations, as described in a later section.…”

Section: Introductionmentioning

confidence: 66%

The global distribution of thermospheric odd nitrogen for solstice conditions during solar cycle minimum

Gérard

Roble

Rusch³

et al. 1984

J. Geophys. Res.

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A two‐dimensional model of the minor neutral constituents N(²D), N(4S), and NO from 70 to 360 km is formulated and used to investigate the global distributions of these species for December solstice conditions during solar cycle minimum. For background properties the zonally averaged circulation, temperature, and compositional structure of major neutral constituents in the thermosphere are obtained from the coupled dynamical chemical model calculations of Roble and Kasting (this issue). Transport of the minor neutral constituents by both the meridional and vertical circulation and vertical molecular and eddy diffusion are considered in the model. The calculated distributions of the minor neutral constituents for solar ionization only and for solar plus auroral ionization are considered. The results show that the summer‐to‐winter pole meridional circulation transports both NO and N(4S) across the solar terminator into the polar night region where there is a downward vertical transport toward the mesosphere. The calculated latitudinal distribution of NO in the lower thermosphere for the solar‐ionization‐only case does not agree with the latitudinal NO distribution usually measured by the Atmosphere Explorer satellites. To obtain agreement between the calculated and observed structure, it is necessary to include ionization and dissociation sources due to auroral particle precipitation. The temperature and compositional structure and the circulation changes caused by high‐latitude heating and the particle‐induced production of N(²D) and N(4S) all combine to bring the calculated NO structure into better agreement with observations. The choice of the eddy diffusion coefficient critically controls the downward flow of thermospheric nitric oxide into the mesosphere. The model shows that the odd nitrogen densities at high winter latitudes are entirely controlled by particle precipitation and transport processes.

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Seasonal and solar cycle variations in the thermospheric circulation observed over Millstone Hill

Cited by 27 publications

References 18 publications

Effects of geomagnetic disturbances on neutral winds and temperatures in the thermosphere observed over Millstone Hill

Effects of geomagnetic disturbances on neutral winds and temperatures in the thermosphere observed over Millstone Hill

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

The global distribution of thermospheric odd nitrogen for solstice conditions during solar cycle minimum

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Seasonal and solar cycle variations in the thermospheric circulation observed over Millstone Hill

Cited by 27 publications

References 18 publications

Effects of geomagnetic disturbances on neutral winds and temperatures in the thermosphere observed over Millstone Hill

Effects of geomagnetic disturbances on neutral winds and temperatures in the thermosphere observed over Millstone Hill

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

The global distribution of thermospheric odd nitrogen for solstice conditions during solar cycle minimum

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