Wind In Equatorial Stratosphere Research Articles

Variations of mean winds and tides in the upper middle atmosphere over a solar cycle, Saskatoon, Canada, 52°N, 107°W

Saskatoon (52 N, 107 W) medium frequency (MF) radar data from 1979 to 1990 have been analyzed to investigate the solar activity effects on upper middle atmospheric winds and tidal amplitudes. The period of study covers two solar maxima and a solar minimum; the continuous data allow a systematic analysis of solar cycle dependence on mean winds and tides. The height region of 79–97 km sampled in the study shows an apparent but very weak dependence of mean winds and tidal amplitudes on solar activity variation. The observed features are fairly consistent with the early results reported by Sprenger and Schmindkr [(1969) J. atmos. terr. Phy. 31, 217). The mean zonal wind and the semidiurnal tidal amplitudes appear to exhibit positive and negative correlations with the solar activity, respectively; the statistical significances of these correlations are generally low. There is a biennial periodicity evident in the zonal wind oscillations but this docs not have a consistent phase relationship with the equatorial stratospheric wind oscillations (QBO). The meridional winds and the tidal amplitudes are characterized with different and quite irregular periods of oscillations (2–5 yr). The diurnal tidal variations over the solar cycle are small and irregular, although amplitudes are slightly larger during the solar minimum years.

Solar variability influences on weather and climate: Possible connections through cosmic ray fluxes and storm intensification

The question of the mechanism for solar‐variability effects on weather and climate can be separated into (1) the identification of the carrier of the solar variability and (2) the identification of the physical link between the carrier and the meteorological response. The suggestion that galactic cosmic rays (GCR), as modulated by the solar wind, are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and considerable evidence for it has now accumulated. Variations of GCR occur with the 11‐year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasi‐biennial oscillation of equatorial stratospheric winds (QBO). Variations in GCR occur on the time scale of centuries with a well‐defined peak in the coldest decade of the little ice age. Here we present new evidence on the meteorological responses to variations on the time scale of a few days. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. The responses reported here include changes in the vertical temperature profile in the troposphere and lower stratosphere and in the northern hemisphere vorticity area index, associated with Forbush decreases in GCR. The meteorological responses to Forbush decreases are in the opposite sense but otherwise are quite similar to responses that immediately follow solar flares. This is to be expected, based on the hypothesis that particles with energy about 100–1000 MeV are the external forcing function for the tropospheric response, since large solar flares increase the particle flux and ionization and minor species production in the lower stratosphere, whereas Forbush decreases reduce them. The mechanism or mechanisms linking changes in low‐energy GCR and other particles in this energy range of 100–1000 MeV to tropospheric temperature and dynamic responses have not been identified. This can be attributed to current uncertainties regarding the microphysical and electrical properties of aerosols and clouds. One possibility is that changes in clouds lead to changes in cloud radiative forcing. The height distribution of the tropospheric response and the amount of energy involved and the rapidity of the time response suggest that the release of latent heat could also be involved. These could lead to the observed tropospheric responses which are understandable in terms of changes in the intensity of cyclonic disturbances. Theoretical considerations link such changes to the observed latitudinal movement of the jet stream.

Observations and statistical simulations of a proposed solar cycle/qbo/weather relationship

The 10.7 cm solar flux is observed to be highly correlated with north pole stratospheric temperatures when partitioned according to the phase of the equatorial stratospheric winds (the quasi‐biennial oscillation, or QBO) (Labitzke and van Loon, 1988a). We supplement their observations with calculations showing that temperatures over most of the northern hemisphere are highly correlated or anticorrelated with north pole temperatures. The observed spatial pattern of solar cycle correlations at high latitudes is shown to be not unique to the solar cycle. We present results similar to the observed solar cycle correlations, with simulated harmonics of various periods replacing the solar cycle. These calculations demonstrate that correlations at least as high as those for the solar cycle results may be obtained using simulated harmonics.

Atlantic Seasonal Hurricane Frequency. Part I: El Niño and 30 mb Quasi-Biennial Oscillation Influences

This is the first of two papers on Atlantic seasonal hurricane frequency. In this paper, seasonal hurricane frequency as related to E1 Niño events during 1900–82 and to the equatorial Quasi-Biennial Oscillation (QBO) of stratospheric zonal wind from 1950 to 1982 is discussed. It is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes, hurricane days and tropical storms, and moderate or strong (15 cases) El Niñ off the South American west coast. A similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and/or are becoming more easterly with time during the hurricane season. This association of Atlantic hurricane activity with El Niño can also be made with the Southern Oscillation Index. By contrast, seasonal hurricane frequency is slightly above normal in non-El Niño years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and/or are becoming more westerly with time during the storm season. El Niño events are shown to be related to an anomalous increase in upper tropospheric westerly winds over the Caribbean basin and the equatorial Atlantic. Such anomalous westerly winds inhibit tropical cyclone activity by increasing tropospheric vertical wind shear and giving rise to a regional upper-level environment which is less anticyclonic and consequently less conductive to cyclone development and maintenance. The seasonal frequency of hurricane activity in storm basis elsewhere is much less affected by El Niño events and the QBO. Seasonal hurricane frequency in the Atlantic and the stratospheric QBO is hypothesized to be associated with the trade-wind nature of Atlantic cyclone formation. Tropical cyclone formation in the other storm basins is primarily associated with monsoon trough conditions which are absent in the Atlantic. Quasi-Biennial Oscillation-induced influences do not positively enhance monsoon trough region vorticity fields as they apparently do with cyclone formations within the trade winds. Part II discusses the utilization of the information in this paper for the development of a forecast scheme for seasonal hurricane activity variations.

Diurnal variation of temperature and wind in the equatorial stratosphere

Diurnal variation of temperature and wind in the equatorial stratosphere

Ozone Variations associated with the Equatorial Stratospheric Wind Oscillations

With a view to elucidate the bi-annual Or possibly 26-monthly oscillation in the ozone content of the atmosphere corresponding to the recently discovered equatorial stratospheric wind oscillation, an analysis was made of the monthly mean total ozone values of five stations, three in India and two in Australia covering the years 1958-1962. When the effects of the annual oscillation are suitably eliminated, it has been found that the long-period variations show a 26-month cycle in the case of four out of the five stations studied. The oscillation seems to extended as far south as 38° Latitude in the southern hemisphere but only as far as 20oN in the northern hemisphere. The amplitude of the 26-month oscillation is greater in the southern hemisphere. Further, the phase of the oscillation is mutually opposite in the two hemispheres. During epochs when the easterly stratospheric winds over the equator at the 25-km level weaken and change over to westerlies, the ozone content increases in the northern hemisphere and decreases in the southern hemisphere. The opposite effect is produced when the westerly stratospheric winds weaken and change over to easterlies.

Possibility of a 26- or 27-Month Periodicity in the Equatorial Geomagnetic Field

Stacey and Westcott1 have presented evidence of an oscillation of somewhat more than two years in the geomagnetic field at one high latitude and three equatorial stations. The importance of this observation lies in its possible connexion with a large amplitude oscillation, of about the same period, in the winds of the equatorial stratosphere2. E. R. Hope, of the Canadian Defence Research Board, early this year, directed our attention to some Soviet literature3,4 on the subject of long-period geomagnetic variations. In these investigations, analyses of geomagnetic data from a number of Soviet stations appear to yield an oscillation of somewhat greater than two years. This work has recently been described by Hope5. Our comments6 accompanying Hope's note point out that the method of analysis may have been responsible for the apparent oscillation. The method of analysis used by Stacey and Westcott, at least in part of their paper (12-monthly minus 24-monthly running means), is similar to that used by Kalinin and Mansurov. In view of the possible implication of oscillations of about the same period in the geomagnetic field and in the equatorial stratospheric winds, a re-examination of the data was felt worth while.

Variations in Ozone associated with the Oscillations of Equatorial Stratospheric Wind

THE recent discovery by Ebdon and Veryard1,2 and by Reed et al.3 of a biannual oscillation in the equatorial stratospheric winds has aroused considerable interest in the physics and dynamics of the stratosphere. It is now well established that the zonal winds in the stratosphere over the equatorial regions of the entire globe alternate in direction between east and west, one cycle of reversal taking a period of about 26 months. An oscillation of a similar period has been observed in the equatorial stratospheric temperatures also. Further, there is evidence from available aerological observations that the biannual wave is propagated slowly downwards from a level at about 30 km or perhaps even higher.

Periodicities of the Geomagnetic Variation Field at Huancayo, Peru

RECENT analyses of stratospheric winds have uncovered the rather fascinating phenomenon of an equatorial stratospheric wind oscillation of approximately 26 months1. Although the apparent wind oscillation seems to have its largest amplitude at about 25 km, it has been suggested by Stacey and Westcott2 that these stratospheric fluctuations extend to ionospheric heights. They performed a spectral analysis of the mean monthly values of the horizontal component of the geomagnetic field on magnetically quiet days, Hq, for Huancayo (12° S.), Apia (14° S.) and Alibag (19° N.). Their results indicated spectral peaks at periods of approximately 26–27 months for Alibag and Apia but not for Huancayo. For all three stations there was also an increase of spectral density at a period of about 12 months. These results were somewhat surprising in view of the fact that at stratospheric levels the maximum amplitude of the 26-month wind fluctuation is found close to the equator and then decreases poleward. Ths amplitude of the annual variation, on the other hand, increases with increasing latitude. The two seem to be equal at a latitude of about 15°. To the extent that ionospheric oscillations as manifested by the oscillation of Hq are related to the stratospheric wind oscillation, one should find the more pronounced 26-month period at the lowest latitude station.