The influence of long-period dynamo region winds on the surface geomagnetic field elements
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Nastrom, G. D.↗
Engineering topics
Nastrom, G. D.
Publications and source records attributed to Nastrom, G. D..
Comparison of periodic and other characteristics of geomagnetic and meterological rocket data
The temporal variations in stratospheric winds and temperatures with the geomagnetic field elements were compared. From a periodic analysis of the geomagnetic field elements the amplitude and phase of the quasibiennial, annual, and semiannual waves are given for stations from 1 degree S to 89 degree N. These results are then compared with corresponding waves reported in rocketsonde wind and temperature data. The annual waves are found to be coupled as a result of the annual variation in the dynamo effect of the wind in the lower ionosphere. The semiannual waves are also found to be coupled and three possible causes for the extra tropical stratospheric semiannual wind wave are discussed. Time variance spectra for the interval from 4 days to 44 days in both zonal winds and horizontal geomagnetic field intensity are compared for years when major midwinter warmings occur and years when only minor warmings occur. The noted differences are suggested to arise from upward propagating planetary waves which are absorbed or refracted in varying amounts depending on the prevailing circulation.
Nastrom, G. D.↗
Diurnal stratospheric tide in meridional wind, 30 to 60 km, by season
The diurnal component in meridional wind is estimated for each season at twelve rocket stations. Amplitudes and phases are presented as a function of height-latitude or as vertical profiles. Many of the gross features of the tide persist throughout the year, but as they migrate in height and latitude the amplitude or phase at a given location may undergo large changes with season. Longitudinal variations in the diurnal tide are found in the mid-stratosphere, and it is suggested they are coupled with longitudinal variations in the tropospheric temperature structure.
Nastrom, G. D.↗
Periodic variations in stratospheric-mesospheric temperature from 20-65 km at 80 N to 30 S
Results on large-scale periodic variations of the stratospheric-mesospheric temperature field based on Meteorological Rocket Network (MRN) measurements are reported for a long-term (12-year) mean, the quasi-biennial oscillation (QBO), and the first three harmonics of the annual wave (annual wave, semi-annual wave, and terannual wave or 4-month variation). Station-to-station comparisons are tabulated and charted for amplitude and phase of periodic variations in the temperature field. Masking and biasing factors, such as diurnal tides, solar radiation variations, mean monthly variations, instrument lag, aerodynamic heating, are singled out for attention. Models of the stratosphere will have to account for these oscillations of different periods in the thermal field and related properties of the wind fields, with multilayered horizontal stratification with height taken into account.-
Nastrom, G. D.↗
Diurnal stratospheric tide in meridional wind, 30 to 60 KM, by season and monthly mean temperatures, 20 to 60 KM, at 80 deg N and to 0 deg N
The diurnal component in meridional wind was observed for each season at twelve rocket stations. Amplitudes and phases are presented as a function of height-latitude or as vertical profiles. Many of the gross features of the tide persist throughout the year, but as they migrate in height and latitude the amplitude or phase at a given location may undergo large changes with season. Longitudinal variations in the diurnal tide are found in the mid-stratosphere, and it is suggested they are coupled with longitudinal variations in the tropospheric temperature structure.
Nastrom, G. D.↗
Periodic analysis of total ozone and its vertical distribution
Both total ozone and vertical distribution ozone data from the period 1957 to 1972 are analyzed. For total ozone, improved monthly zonal means for both hemispheres are computed by weighting individual station monthly means by a factor which compensates for the close grouping of stations in certain regions of latitude bands. Longitudinal variability show maxima in summer in both hemispheres, but, in winter, only in the Northern Hemisphere. The geographical distributions of the long term mean, and the annual, quasibiennial and semiannual waves in total ozone over the Northern Hemisphere are presented. The extratropical amplitude of the annual wave is by far the largest of the three, as much as 120 m atm cm over northern Siberia. There is a tendency for all three waves to have maxima in high latitudes. Monthly means of the vertical distribution of ozone determined from 3 to 8 years of ozonesonde data over North America are presented. Number density is highest in the Arctic near 18 km. The region of maximum number density slopes upward toward 10 N, where the long term mean is 45 x 10 to the 11th power molecules cm/3 near 26 km.
Wilcox, R. W.↗
Periodic variations in stratospheric meridional wind from 20 to 65 km - 80 N to 70 S
Long-term periodic features in the meridional wind between 20 and 65 km attitude are analyzed. No appreciable periodic waves are found in the tropics. The quasi-biennial oscillation, annual wave, and four-month wave have maximum amplitudes of about 10, 20, and 10 m/s respectively in the arctic near 45 km. The phase of the annual wave changes by nearly 180 deg in a narrow zone near 45 deg N. The semiannual wave has an amplitude of 10 m/s near 50 deg N above 50 km with equinoctial phase dates in the region of maximum amplitude. The location of this polar semiannual wave corresponds closely to that previously found in the zonal wind.
Nastrom, G. D.↗
Periodic variations stratospheric temperature from 20-65 km at 80 deg N to 30 deg S
Results for a seasonally varying diurnal tide in temperature at Churchill are presented, and possible significant aliasing of longer period waves by this tide is discussed. A diurnal tide whose amplitude and phase are coherent throughout the year is found to have little effect on periodic amplitudes other than the long-term mean, because most rocketsonde observations are taken near the same local time each day. Errors in periodic components arising from lack of solar radiation corrections are found to be largest for the long-term mean with a small influence noted in the annual wave's amplitude. Spatial variations of the amplitudes and phases of long-period waves are examined through the use of height-latitude sections, 20-65 km, at 80 deg N to 30 deg S. The quasi-biennial oscillation and semiannual waves have tropical maxima of 2 and 3C near 30 and 40 km respectively. The annual wave's maximum is over 22C near 45 km at 70 deg N and the terannual wave's maximum is over 6C near 55 km at 80 deg N. The semiannual wave has to polar maxima: 7C near 75 deg N at 32 km and 3C above 60 km north of 35 deg N.
Nastrom, G. D.↗
Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind
The polar semiannual oscillation in zonal wind explains midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summer easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that the polar wind oscillations are caused by the semiannual maxima in magnetic storm activity, which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.
Belmont, A. D.↗
Significance of semiannual waves in the mesospheric zonal wind and evidence of influence by the geomagnetic field
The recently described polar semiannual oscillations in zonal wind can explain midwinter weakening of the polar winter vortex and the relatively short stratospheric and mesospheric summer easterlies. This explanation implies that stratospheric sudden warmings may be caused or affected by the polar semiannual oscillation. Two potential physical mechanisms (not mutually exclusive) for the oscillation are presented: planetary wave action and changes in the radiation field. Radiation absorption changes are suggested to result from changes in ozone concentration during magnetic storms. Contours of amplitude of both the polar and tropical semiannual wind oscillations are more nearly congruent with geomagnetic than with geographic latitude.
Belmont, A. D.↗
Periodic variations in stratospheric meridional wind from 20-65 km, at 80 deg N to 8 deg S
The variability of stratospheric meridional winds is examined in both space and time. Height-latitude sections for January along 70 deg E and 90 deg W show a divergence zone above 50 km near 60 deg N and an intense convergence zone 40 km near 50 deg N over North America. This latter structure, with southward winds in the Arctic and northward winds at mid-latitudes over North America, persists from October through April. Tidal winds dominate all other circulation features in summer at all latitudes, and throughout the year at low latitudes. To help understand the observed patterns of variability, long-term periodic features are analyzed. The quasi-biennial oscillation, annual wave, and four-month wave have amplitudes of about 10, 20, and 10 m/sec respectively in the Arctic near 45 km. The phase of the annual wave changes by nearly 180 deg in a narrow zone near 45 deg N. The semiannual wave has an amplitude of 10 m/sec. 50 deg N above 50 km equinoctial phase dates in the region of maximum amplitude. This polar semiannual wave corresponds closely to that previously found in the zonal wind.
Nastrom, G. D.↗
Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind
The polar semiannual oscillation in zonal wind can explain midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summar easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that polar wind oscillations are caused by the semiannual maxima in magnetic storm activity which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and thereby inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.
Belmont, A. D.↗
Suggested causes of latitudinal asymmetries of periodic variations of the stratospheric zonal wind
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Belmont, A. D.↗
Variability of the observed temperature, 20-60 km at 80 deg N to 40 deg S
Results are presented for a periodic analysis of atmospheric temperature variations at heights of from 20 to 60 km between 80 deg N and 40 deg S. The analysis is based on Meteorological Rocket Network temperatures not corrected for solar radiation or aliasing by the diurnal tide, and the frequencies examined include the long-term mean, the quasi-biennial oscillation (QBO), and the first six harmonics of the annual wave. Amplitudes are plotted for the long-term mean and QBO as well as for the annual, semiannual, and terannual components. The results show two distinct annual oscillations (the high-latitude one and another above the tropical stratopause) and a polar semiannual wave with two centers of large amplitude that are 90 deg out of phase and separated by a zone of minimum amplitude near 45 km.
Nastrom, G. D.↗