Storm Of February Research Articles

Spherical asymmetry in thermospheric magnetic storms

During moderate magnetic storms, changes in the neutral composition suggest that energy is deposited in the auroral zones. This results in thermal expansion (enhancement in N 2, Ar) and consequent redistribution of the lighter species O and He such that their densities decrease at high latitudes and increase at low latitudes. From measurements obtained by the ESRO 4 gas analyzer during a major storm in late February 1973 ( K p = 7 +) these typical high latitude characteristics were observed in the southern hemisphere and at certain longitudes to extend toward mid and low latitudes as far as −20° invariant latitude. Further examination of these data for latitudes across the equator up to +20° latitude, however, shows evidence for an enhancement zone in He and O which is clearly displaced into the northern hemisphere thus suggesting a pronounced spherical asymmetry. Ground based observations on the state of the ionosphere between ±50° latitude confirm this asymmetry and suggest that the center of this enhancement zone occurs at about +15° invariant latitude. Adopting a suitable energy distribution in both hemispheres the magnetic storm response in the neutral composition is simulated with a circulation model. From this analysis it is concluded that for some longitudes a difference of a factor of two or more between the heating rates of the northern and southern hemispheres is required to match the ESRO-4 data.

Significance of large-scale circulation in magnetic storm characteristics with application to AE-C neutral composition data

Theoretical analysis of a magnetic storm in February 1974 leads to the following conclusions: (1) Wind-induced diffusion leads to depletion of O and He and enhancements of Ar at high latitudes. (2) The same process increases O and He and decreases Ar at low latitudes. (3) There is substantial agreement between theory and neutral composition data from the AE-C closed source neutral mass spectrometer; the low-latitude enhancements of O and He, in magnitude comparable to or even larger than those of N2 and Ar, are observed, which is characteristic for the circulation mechanism. (4) To achieve agreement with the composition measurements, a heat input rate of 1.7 ergs/cm² s is required above 120 km. (5) Changes in the neutral composition associated with the annual variations have significant effects on the magnetic storm dynamics.

Esro 4 Gas Analyzer results 3. Spatial and temporal structure of the mid-latitude atmosphere during a geomagnetic storm

Neutral atmospheric composition measurements were obtained by the Esro 4 gas analyzer during a series of geomagnetic storms in late February 1973. Complemented by ground-based ionosonde data, these measurements show a complex latitudinal and longitudinal structure of the storm-associated disturbances in the upper atmosphere. Specifically, a strong depression of the O/N2 ratio developed and persisted for several consecutive days above the Australian-African area. It was distinguished by a fairly sharp eastward boundary near 180°E longitude. This mid-latitude disturbance zone was distinctly separated from strongly disturbed regions at higher latitudes. It is suggested that the energy causing this mid-latitude disturbance was deposited primarily at altitudes below 150 km. Because of the long diffusion time constants in the lower thermosphere this can account for the persistence of the phenomena observed at F2 layer heights.

Development of four magnetic storms in February 1972

Four magnetic storms were observed in February 1972, with instruments on the Explorer 45 satellite in the evening quadrant of the inner magnetosphere. The magnitude of the storms ranged from small, D st ≅ −40 γ, to moderate, D st ≅ −80 γ. During the development of the storms several substorms occurred. At the beginning of the substorms there was evidence of a partial ring current above L = 5. After the expansion phase of several substorms there was evidence of enhancement of a partial ring below L = 5. Distortions of the field in the east-west direction were observed, in conjunction with substorm expansions, that can be interpreted as due to field aligned currents flowing from the ionosphere. A substantial symmetric ring current, at L∼4, developed during the largest storm. Very little additional ring current was contributed by the smallest storm. Relations between the magnetosphere inflation and ring current protons, plasmaspheric hiss, and ULF waves also measured on Explorer 45 were noted.

Evolution of disturbance daily variation (DS) and interplanetary plasma parameters

The evolution of DS during the storms of February 7 and February 16, 1967 and October 31, 1968 is studied. It is shown that DS usually evolves as a morning maximum and a dusk minimum but not necessarily simultaneously. Also, the maxima and minima may shift to other LT sectors too. DS continues to be high even in the recovery phase and generally ends up as anoon-time decrease. DS seems to be related with solar wind parameters N and V but not with interplanetary magnetic field.

Esro 4 Gas Analyzer results 2. Direct measurements of changes in the neutral composition during an ionospheric storm

Direct measurements of the neutral composition at ionospheric heights with the gas analyzer aboard Esro 4 reveal large decreases in the atomic oxygen to molecular nitrogen ratio during the ionospheric storm in late February 1973. A comparison shows that these changes in the neutral composition correlate well with decreases in the F2 layer critical frequency observed at different ionosonde stations. The data presented therefore strongly support previous theoretical studies that delineate neutral composition changes as the major cause for negative ionospheric storm effects. It is suggested that ionospheric and neutral upper atmospheric storm data could be used to supplement each other.

Marine Conditions and Automated Forecasts for the Atlantic Coastal Storm of February 18–20, 1972

Abstract The storm surge and ocean waves associated with the Atlantic coastal storm of Feb. 18–20, 1972, caused extensive damage along beaches of Long Island and New England. Meteorological conditions of the storm, along with resulting tides, surges, and waves, are described. Comparison is made with forecasts of the storm produced by the primitive-equation model of the National Meteorological Center, as well as with automated forecasts of storm surge and wave height. It is concluded that the meteorological forecasts and the resulting storm surge and wave forecasts were quite good.

Isis 1 observations of the high-latitude ionosphere during a geomagnetic storm

The Isis 1 satellite has made measurements of several ionospheric and related parameters, and the results of the various measurements have been compared in detail for two north transpolar passes during the geomagnetic storm of February 3, 1969. Simultaneous measurements were made of local electron and ion densities and temperatures, electron density between the satellite and the peak of the F layer, radio noise, and particle fluxes over a wide energy range extending down to 10 eV. Several features of the ionosphere (in particular, enhancements of radio noise, scale height, and plasma temperatures) appear to be due to soft-particle (100 eV to 1 keV) precipitation, which is related to magnetospheric structure as delineated by the observation of more energetic particles. The magnetosheath particles precipitating on the dayside of the polar cap are particularly effective.

Magnetosphere inflation during four magnetic storms in 1965

Study of four magnetic storms in 1965, using Explorer 26 and ground observatory magnetic data, shows that both small and large magnetic storms develop through initial asymmetric inflation of the evening magnetosphere. Development times vary from 6 to 36 hours, and the development is sometimes interrupted. The inflating particles are injected as deep as L = 3 during the development phase in large storms but only to L = 4 in smaller storms. In the slow recovery phase there is a clear relation between the magnitude of the inflation and the location of the inflation belt. The April storm belt with 100-γ inflation at the beginning of slow recovery was at L = 3.7, whereas the February storm with 30-γ inflation was at L = 4.8. An unusual distortion of field direction on June 16 is interpreted as evidence for current flow along field lines at the onset of a substorm.

Interplanetary field and geomagnetic variations—a unifield view

The relationship between interplanetary magnetic fields seen by the Ames magnetometer on board Explorer 33 and surface magnetic variations has been studied. The emphasis of the study is toward achieving a unified view of all the experimental results, both of this study and previous studies. Various statistical studies of the relationship between K p and parameters of the solar wind were carried out. The effect of the direction of the z component of the interplanetary field is confirmed. In all other statistical studies the data were divided into two groups, one in which the 3-hr average field pointed northward, and the other in which it pointed southward. In this way, we show, for example, that the tendency toward an association of high K p with intense interplanetary fields is independent of the North-South effect. Other statistical investigations were also carried out. The Sun was considerably disturbed during the period covered by this study, giving an excellent opportunity to observe the magnetic configuration of flare-induced interplanetary storms and their relation to geomagnetic storms. The interplanetary storm was found to be typified by persistent, strong fields (up to 30 γ) that rise far out of the ecliptic plane. As discussed below, this is to be expected on the basis of simple models. Further, it was found that high-velocity plasma and intense, highly disturbed interplanetary fields are also typical of interplanetary storms. The close association of these parameters in the interplanetary medium is one cause of confusion in interpretations of geomagnetic studies. During the flare-produced storm of February 15, 1967, there was a remarkably close temporal association between events in space and on the surface. This event is discussed in detail.

Contribution à l'étude des relations entre les activités solaire et géomagnétique

The article states the necessary conditions under which geomagnetic storms and disturbances arise, as revealed by observations of the Sun. The new criteria do not conflict with those previously developed, based on other phenomena. On the strength of these new ideas a method for forecasting geomagnetic activity has been elaborated, enabling a sudden commencement to be predicted with great accuracy. It makes possible the forecasting of geomagnetic storms in each period of the solar cycle, and to say in advance whether the onset of a given storm will be sudden or gradual. As examples for the purpose of explaining their origin, use has been made of the suddencommencement geomagnetic storms of llth February 1958, 20th September 1959, 29th October 1963, and 22nd November 1963. Except for the first, all these storms had been predicted on the basis of observations of the Sun by means of the spectrohelioscope. Furthermore, an explanation is given of the origin of the gradual-onset geomagnetic storm of 6th and 7th October 1960, which had likewise been predicted. On the same principles explanations are given of the geomagnetic quiet period of 19th–25th June 1965, which recurred six times (16th–17th July, 13th August, 8th–9th September, 6th–7th October, 1st–3rd November and 28th–29th November 1965) and of the one that occurred twice—on 31st December 1965 and 1st January 1966 and on 27th–28th January 1966.

Solar protons and magnetic storms in February 1962

The satellite Injun 1 (1961o2) detected solar protons during February 2–7, 12, and 20–23, 1962. We will discuss the first of these three periods in detail, with only a brief reference to the following relatively smaller events. Injun 1 was designed and built at the State University of Iowa. It is described in detail by O'Brien and Whelpley [1962]. The satellite was launched on June 29, 1961, and is in an orbit of inclination 66.8°, apogee altitude 998 km, perigee altitude 881 km, and period 104 minutes; the orbit carries the satellite to a geomagnetic latitude of 78°. Injun's fourteen radiation detectors include an APL package of four silicon p–n junction detectors [Pieper, 1961] and a SUI spectrometer background Geiger counter that is sensitive to protons with energy above 40 Mev and forms part of a magnetic electron spectrometer developed by Laughlin [1960] and also described by O'Brien, Van Allen, Laughlin, and Frank [1962]. The APL unit has two orthogonally mounted pairs consisting of detector PNA with its background monitor PNB and PNC with its monitor PND. Detectors PNA and PNC are sensitive to protons in the energy ranges 1.4–17 Mev and 1.6-11 Mev, respectively. As in earlier reports, for brevity we treat the PN energy ranges as 1–15 Mev.

AN INVESTIGATION OF BROADSCALE VERTICAL MOTIONS AND PRECIPITATION IN AN EASTERN NORTH AMERICAN STORM

The precipitation associated with the intense storm of February 25–27, 1961, which affected eastern North America, is investigated. Vertical motion patterns are computed for successive days of the storm using a method suggested by Bushby, and based on the Sutcliffe development theory. These patterns are used, together with different, rate of precipitation formulas, to calculate, precipitation amounts. Comparisons with actual amounts are made. A method of quantitative precipitation forecasting is suggested.

Polar-cap absorption and the magnetic storm of February 11, 1958

For l2 hr preceding the storm, polar-cap absorption indicated a fiux of actinic radiations at 10 to 100 Mev near the earth. A solar flare of 2/sup +/ importance produced the storm. Effects on energetic particles near the earth are discussed. Cosmic-noise absorption was recorded using high-latitude riometers. Data are presented in graphical form. (L.N.N.)

North–South Anisotropy and Anticipatory Increase of Intensity Associated with the Cosmic-Ray Storm of February II, 1958

Solar and terrestrial observations associated with the cosmic-ray storm of February 11, 1958, are discussed relative to North-South anisotropy and the anticipatory increase of intensity. A chronology of events associated with the Forbush Decrease of February 11 is given and the connection between these events is discussed. (C.J.G.) expcsures, The charge spectra, flux, mean free paths, and angular distributions are given. (auth)

Auroral x-rays, cosmic rays, and related phenomena during the storm of February 10-11, 1958

Balloon observations were made during the auroral storm of February 10- 11, 1958, at Minneapolis. Strong x-ray bursts in two groups were detected. The groups appeared coincident with two large magnetic bays, with strong radio noise absorption, and with the passage across the zenith of a very large amount of auroral luminosity. From the x-ray intensity and measured energies, an electron current of 0.6 x 10/sup 6/ electrons /cm/sup 2// scc was present. These electrons ionizing the upper D layer accounted for the increased cosmic noise absorption. The x-rays themselves carried 1000 times less energy than the electrons and could not provide sufficient ionization for the observed radio absorption. Visual auroral fornis during this storm are reported to have lower borders at thc 200 to 300 km level. There is thus a difficulty in bringing the electrons to the D layer without ani accompanying visible aurora. A cosmic-ray decrease accompanied the storm and was observed to be from 4 to 6% at sea level, 21% in the balloon altitude ionization, and 15% in total energy influx at 55 deg geomagnetic latitude. Compared with the great intensity of the magnetic and auroral phenomena in this storm, the cosmic-ray modulation was notmore » exceptionally large. (auth)« less

The electro-magnetic state in interplanetary space during the flare of feb. 23, 1956

The increase in cosmic-ray intensity in connection with the solar fiare of February 23. 1956. was observed at different places around the earth to have started at different times. This means that cosmic-ray particles which have been produced in the vicinity of the sun must have travelled along orbits of different length before reaching the earth. It has been possible to cornect the onset time observed at a particular station with certain directions outside the geomagnetic field. The results of the study indicate that those particles which arrived first st the earth did not travel along straight lines from the sun. This proves the existence of deflecting fields between the sun and the earth. Two days after the flare increase. a heavy magnetic storm was registered. There is evidence that magnetic storms are caused by the electric fleld set up in a field of ionized gas which is enfitied frnm the sun. It is assumed that the magnetic storm of february 25 was caused by such a beam. lt is assumed that solar flare cosmic particles can not escape from the vicinity of the sun until they have entered the beam. (A.C.)

Sudden Decrease in Low-frequency Atmospheric Noise during the Cosmic-Radiation Storm of February 23

AT Churchill, Manitoba (lat. 58.8° N., long. 94.2° W.), an unusual event occurred on the 100-kc./s. atmospheric noise recordings on the morning of February 23. Churchill is situated near the region of maximum intensity of the auroral zone.

THE FEBRUARY MINIMUM IN HAWAIIAN RAINFALL AS A MANIFESTATION OF THE PRIMARY INDEX-CYCLE OF THE GENERAL CIRCULATION

The climatic minimum in rainfall observed in February at most stations in the Hawaiian Islands is ascribed to the expansion of the circumpolar westerly vortex of the mid-troposphere incident to the annual primary index-cycle. The southward migration of the westerlies in February and early March results in weakening the trade winds, thereby reducing the trade component of Hawaiian rainfall. The migration also makes possible a longer stationary wavelength between the climatologically “anchored” Asiatic coastal trough and the next down-stream trough, whose position with respect to the islands is critical in that it frequently brings kona storms in January but comparative freedom from such storms in February. The trade-wind regime is restored in strength during March when rainfall again increases. Numerous statistics are cited to establish the reality and time scale of the rainfall minimum and its relation to the index cycle.

EVOLUTION OF THE KONA STORM A SUBTROPICAL CYCLONE

Abstract Two sources of kona-storm development in the eastern Pacific are studied, together with factors leading to storm intensification. Vertical structure of this subtropical cyclone is considered in terms of sounding data from Hawaiian stations during the storms of February and March 1951. The kona cyclone initially possesses cold-core characteristics, with winds and rainfall amounts increasing with distance from the low-pressure center and reaching a maxima at a radius of 200 to 500 mi. However, with intensification, this cyclone may develop warm-core properties, with rainfall and wind profiles bearing marked resemblance to those of the tropical cyclone.