Neutral thermospheric winds deduced above Millstone Hill, 2. Seasonal wind variations, 1970–1971

Emery, B. A.

doi:10.1029/ja083ia12p05704

Cited by 18 publications

(7 citation statements)

References 34 publications

(39 reference statements)

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“…From the results presented here, it appears that the seasonal pattern in the winds seen by Emery [1978b] (2)). Because of the large scatter in the data the fit is not statistically significant; however, there is a general trend of eastward winds in winter and westward winds in summer, with no apparent change in the pattern over the solar cycle.…”

Section: Discussionmentioning

confidence: 53%

“…Near equinox there is a short-lived transition period (3-4 weeks) in which the global circulation is relatively symmetric. The meridional mass flow patterns shown in Figure 1 To date, the largest sample of thermospheric wind measurements used to examine this wind pattern has been presented by Emery [1978b]. Using neutral winds and temperature data derived from ionospheric measurements made at Millstone over the 2-year period 1970-1971 as input to a semiempirical dynamic model, Emery confirmed the persistence of this pattern over the 2-year period 1970-1971.…”

Section: Introductionmentioning

confidence: 77%

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

Babcock¹,

Evans²

1979

J. Geophys. Res.

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Incoherent scatter measurements of the ionospheric F region electron density, electron and ion temperature, and vertical ion drift made at Millstone Hill have been used to derive estimates of the exospheric neutral temperature T∞ and the horizontal component of the neutral wind along the magnetic meridian VHn. These data then were employed in a semiempirical model for the local thermosphere (Emery, 1978a) to calculate the diurnal variation of the zonal and meridional winds for the days of the measurements. A total of 64 geomagnetically quiet days from the years 1970, near solar maximum, through 1975 were analyzed. The mean meridional and zonal winds were found to exhibit a marked seasonal variation of about ±50 and ±30 m/s, respectively. The amplitude of this oscillation did not appear to decrease with decreasing sunspot activity; however, the annual mean meridional wind was found to decrease from 25 m/s equatorward to about 0 m/s over the 6‐year period. It is believed that this is indicative of a decrease in the auroral forcing relative to the solar forcing at solar minimum. The meridional winds near equinox shifted from being generally equatorward at solar maximum to being poleward at solar minimum, also suggesting decreased auroral forcing. The diurnally averaged zonal winds maintained a fairly consistent pattern of eastward winds in winter and westward winds in summer over the 6‐year interval.

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Section: Discussionmentioning

confidence: 53%

Section: Introductionmentioning

confidence: 77%

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

Babcock¹,

Evans²

1979

J. Geophys. Res.

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“…These results suggest that the assumed estimate of interhemispheric differences in auroral heating may be high by a factor of 2. However, comparison between the calculated and measured zonal average north/south velocity as done by Emery [1978] suggest a smaller reduction of about 30% is needed. We regard the velocity measurements as a somewhat more sensitive index of the auroral heating, so that we believe the average auroral heating rates we used here and in previous papers are likely to be high by approximately 30%-40%.…”

Section: Results For Solsticementioning

confidence: 99%

A three‐dimensional general circulation model of the thermosphere

Dickinson¹,

Ridley²,

Roble³

1981

J. Geophys. Res.

382

221

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The global neutral gas temperature distribution and circulation of the thermosphere are calculated for equinox and solstice conditions by using NCAR's thermospheric general circulation model (TGCM). The variables are determined on a 5° grid in latitude and longitude at 24 constant pressure surface layers in the vertical from about 90 to 500 km. Global empirical models of electron density and neutral composition are used to specify ion drag and the neutral gas background properties. The energy sources that drive the thermosphere include heating caused by the absorption of solar EUV and UV radiation and a high‐latitude heat source associated with auroral processes. Starting from a global average state, the TGCM reached a diurnal reproducible pattern in approximately 5 days and showed no apparent instabilities in the basic flow. The calculated motion patterns indicate that the observed day‐to‐day variability in the thermosphere is likely because of variations in the heat and momentum sources such as the result of neutral plasma interactions and waves coming from the lower atmosphere. The calculated horizontal structure of wind and temperature is qualitatively different between the upper and lower thermosphere. This difference occurs because the diurnal and semidiurnal forcing are in phase in the optically thick lower thermosphere but out of phase in the optically thin upper thermosphere. Using the latest calculated heating efficiencies and measured fluxes of EUV, the calculated diurnal temperature amplitude is 250 K, compared to 320 K predicted by the MSIS empirical model, indicating that solar heating is primarily responsible for maintaining the structure of the thermosphere. The zonally averaged properties of the TGCM essentially agree with previous results obtained from a two‐dimensional model of the zonally symmetric thermosphere. However, for reasons discussed, the latitudinal variations of temperatures is somewhat larger than previously calculated. Our previously estimated auroral heating terms need to be reduced by 30%–40% to get best agreement with observations.

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“…In one of the earliest seasonal analyses of ISR derived winds Emery (1978) used solar maximum data at 43 • N to show a large seasonal change in mean southward wind from about +70 ms −1 in summer to 30 ms −1 in winter. On comparison with the data presented here it is interesting to note that neither of the measurement based climatologies, i.e.…”

Section: Summary Of the High Solar Activity Comparisonsmentioning

confidence: 99%

Comparison of high-latitude thermospheric meridionalwinds II: combined FPI, radar and model Climatologies

et al. 2004

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Abstract. The climatological behaviour of the thermospheric meridional wind above Kiruna, Sweden (67.4°N, 20.4°E) has been investigated for seasonal and solar cycle dependence using six different techniques, comprising both model and experimental sources. Model output from both the empirical Horizontal Wind Model (HWM) (Hedin et al., 1988) and the numerical Coupled Thermosphere and Ionosphere Model (CTIM) are compared to the measured behaviour at Kiruna, as a single site example. The empirical International Reference Ionosphere (IRI) model is used as input to an implementation of servo theory, to provide another climatology combining empirical input with a theoretical framework. The experimental techniques have been introduced in a companion paper in this issue and provide climatologies from direct measurements, using Fabry-Perot Interferometers (FPI), together with 2 separate techniques applied to the European Incoherent Scatter radar (EISCAT) database to derive neutral winds. One of these techniques uses the same implementation of servo theory as has been used with the IRI model. Detailed comparisons for each season and solar activity category allow for conclusions to be drawn as to the major influences on the climatological behaviour of the wind at this latitude. Comparison of the incoherent scatter radar (ISR) derived neutral winds with FPI, empirical model and numerical model winds is important to our understanding and judgement of the validity of the techniques used to derive thermospheric wind databases. The comparisons also test model performance and indicate possible reasons for differences found between the models. In turn, the conclusions point to possible improvements in their formulation. In particular it is found that the empirical models are over-reliant on mid-latitude data in their formulation, and fail to provide accurate estimates of the winds at high-latitudes. Key words. Meteorology and atmospheric dynamics (thermospheric dynamics), Ionosphere (ionosphere-atmosphere interactions, auroral ionosphere)

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Neutral thermospheric winds deduced above Millstone Hill, 2. Seasonal wind variations, 1970–1971

Cited by 18 publications

References 34 publications

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

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

A three‐dimensional general circulation model of the thermosphere

Comparison of high-latitude thermospheric meridionalwinds II: combined FPI, radar and model Climatologies

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