Storm Of February Research Articles

Radar and satellite observations of the storm time cleft

During the magnetic storm of February 8–9, 1986, the region of strong ion convection in the vicinity of the dayside cusp expanded equatorward into the field of view of the Millstone Hill radar at lower mid‐latitudes. High‐speed (>1.5 km s−1) poleward ion flows were found at latitudes as low as 60° invariant latitude, at least 10° lower than the typical cleft/cusp position for moderately disturbed (Kp>4) magnetospheric conditions. The ion velocity pattern responded promptly to changes in the interplanetary magnetic field By direction. The large‐scale two‐dimensional convection pattern across the dayside was well resolved using radar azimuth scan data at Millstone Hill, thus enabling us to place the fine‐scale radar/satellite observations of the storm time cusp and cleft in the context of the large‐scale pattern. We present a detailed comparison of radar and DMSP F7 satellite observations in the prenoon sector during a period of Kp > 7, to examine the low‐altitude signatures of various plasma regions in the vicinity of the cusp. The combination of particle precipitation, magnetic field perturbation, radar measurements of ion heating, and convection consistently suggests the unusual low‐latitude position of cusp at 65° invariant latitude. Boundary plasma sheet particles were observed to coincide with a narrow region of magnetic‐field‐aligned currents, and with antisunward convection flows at the equatorward edge of the cleft. This may be an indication of the presence of a viscous cell. The radar and satellite observations indicate that the storm time cleft and cusp at ionospheric altitudes retain the general characteristics revealed in their average configuration. Particle and field signatures of the plasma sheet, plasma sheet boundary layer, low‐latitude boundary layer, cusp, and mantle are identified at unusually low magnetic latitude in the 9–10 magnetic local time sector during this event.

Precipitating and trapped ions and electrons observed at 840 km during the Great Magnetic Storm of February 1986

A detailed picture is presented of the equatorward boundaries of the auroral ovals at dawn, morning, dusk, and evening for the three most disturbed days of February 1986. North–south symmetry for the boundaries of keV particles was good, and the differences between the ion and electron boundaries agreed with statistics which show the ion edge slightly equatorward of the electron edge at dusk, with the reverse for dawn. The electron boundary was most equatorward of the ion boundary for morning. Best symmetry and least difference were for evening, the sector nearest the central plasma sheet. Ions with energies from thermal to several hundred electron volts penetrated inward to L = 1.2. Initial penetration was confined mainly, if not exclusively, to the dawn sector. The sudden appearance of low‐energy ions deep in the plasmasphere at dusk and evening after storm maximum suggests corotation from a plasmapause as low as L = 1.7 at dawn. Low‐energy electrons rarely advanced equatorward of the keV electrons. On the other hand, keV electrons occasionally were detected about the equator, apparently in relation to the inward convection of the radiation belt. Very energetic, MeV, particles occurred near 52° MLAT, mainly after storm maximum and often unsymmetrically, which may reflect a characteristic akin to the South Atlantic Anomaly.

Simultaneous relativistic electron and auroral particle access to the polar caps during interplanetary magnetic field Bz northward: A scenario for an open field line source of auroral particles

The large magnetic storm of February 1986 provides a unique opportunity to assess whether existing open‐closed theories of the magnetosphere can consistently account for precipitating particle signatures measured at 840 km under a wide variety of solar wind and solar particle conditions. Here we report the simultaneous observation of relativistic electrons associated with a solar proton event and of auroral ions and electrons associated with a polar cap arc event, made across the central polar cap using detectors on board the Defense Meteorological Satellite Program (DMSP) satellites. On February 7 while a solar proton event was still in progress, polar cap arc activity (interplanetary magnetic field (IMF) Bz large and positive, Kp = 3+) occurred prior to a prolonged period of oval arc activity (IMF Bz large and negative, Kp = 6−). Throughout these periods the following are identified: the equatorward edge of the relativistic electron precipitation; the outer zone electron poleward and equatorward boundaries; the equatorward auroral electron and ion boundaries; and the auroral electron transition boundary. The history of the boundaries is presented as the transition from intense polar cap activity to intense auroral oval activity takes place. The data clearly show that the polar cap region of relativistic electron precipitation does not change significantly as the sign of Bz changes. On the other hand, the boundary layer population, which contains auroral arcs and 1‐ to 10‐keV ion precipitation, expands to fill most of the polar cap for Bz northward and greatly contracts as Bz turns southward. The expansion is not symmetric between poles. The fact that in a broad region of the central polar cap, auroral arcs and relativistic electrons are found on the same field lines presents some difficulty for jointly maintaining theories that propose the formation of polar cap arcs strictly on closed field lines and theories that explain relativistic electron entry by means of direct access along open field lines. We argue that the data support polar cap arc formation on open field lines and present a scenario in which the tail lobe boundary plasma is the source of auroral particles at high latitudes.

Radiation belt dynamics during solar minimum

Two types of temporal variation in the radiation belts are studied using low-altitude data taken onboard the DMSP F7 satellite: those associated with the solar cycle and those associated with large magnetic storm effects. Over a three-year period from 1984 to 1987 and encompassing solar minimum, the protons in the heart of the inner belt increased at a rate of approximately 6% per hear. Over the same period, outer zone electron enhancements declined both in number and peak intensity. During the large magnetic storm of February 1986, following the period of peak ring current intensity, a second proton belt with energies up to 50 MeV was found at magnetic latitudes between 45 degrees and 55 degrees . The belt lasted for more than 100 days. The slot region between the inner and outer electron belts collapsed by the merging of the two populations and did not reform for 40 days.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Explosive East Coast Cyclogenesis: Numerical Experimentation and Model-Based Diagnostics

Numerical experimentation of explosive east-coast cyclogenesis is performed using the Florida State University Global Spectral Model (FSUGSM). The three cases examined here are the Presidents' Day storm of February 18-19, 1979 and the North Atlantic and Pacific bombs of January 18-20, 1979 which formed off the east coasts of the United States and Japan, respectively. The use of a global model provides a framework for studying the phenomena on the 3-5 day time scale. The forecast verifications of the numerical experiments indicate that the FSUGSM was able to adequately predict the phase, intensity, and synoptic-scale structure. These results justify the use of model data for diagnostic studies of the bomb. The model data are used to quantify the role of the adiabatic and diabatic forcing in the explosive cyclogenetic process, using surface pressure tendency to gage development.

Sc- and Si-associated ULF and HF-Doppler oscillations during the great magnetic storm of February 1986.

Results are presented of an investigation of SC- and SI-associated ULF and HF-Doppler pulsations observed during the great geomagnetic storm of February 1986, which began with a sudden commmencement on February 6 at about 13:12 UT, developed slowly over the next two days, and, after a rapid intensification late on February 8, reached a minimum. It is shown that these ULF and geomagnetic pulsations can be explained by the dynamo-motor mechanism of ionospheric electric fields and by global compressional oscillations in the magnetosphere and ionosphere, respectively.

The ion energy spectra in the ring current during the geomagnetic storm of February, 1986

Using data from the CHEM instrument on the AMPTE/CCE spacecraft, we follow the development of the ring current energy spectra (1–300 keV/e) of the ion species H +, O +, He +, and He ++ in the post-noon and pre-noon local time sectors during the geomagnetic storm of February 1986. By comparing displays of phase space density, f, vs. magnetic moment, μ, we can distinguish between enhancements due to newly injected ions and those due to adiabatic energization of a pre-existing population. In both the local time sectors, the initial drop in Dst is associated with enhanced phase space densities of all species. The spectra observed during the pass when the Dst dropped to a minimem of −312 nT show a strong local time asymmetry. In the post-noon sector, the spectra showed the influx of a new population of ions, rich in O + and He ++. In the pre-noon sector, the flux increase was consistent with adiabatic energization of the ion population injected earlier in the storm. This local time difference is consistent with a greatly enhanced convection electric field which brings a new population from the magnetotail to the post-noon, but not the pre-noon local time sector.

Ionospheric incoherent scatter measurements with the middle and upper atmosphere radar: Observations during the large magnetic storm of February 6‐8, 1986

The middle and upper atmosphere (MU) radar of Japan is a 46.5‐MHz, pulse‐modulated, monostatic, Doppler radar with an active phased‐array antenna which consists of 475 crossed yagis. This system has been used primarily, since its initial observations with a partial system in 1983, to observe the coherent backscatter from irregularities in the troposphere, stratosphere, and mesosphere (MST radar). However, this system was also designed to be able to observe the weak incoherent scatter (IS) from the free electrons of the ionosphere. We report here the MU radar IS observations made during the strong geomagnetic storm of 6–8, February 1986. During this period the MU radar observed the echo power (an approximate measure of electron density) simultaneously in four antenna beam positions. Coincident with the rise in the Kp index from 3+ to 6− near 1800 LT (0900 UT) on February 7, the MU radar detected the beginning of several hours of wave activity having a period of 100 min. By correlating the density observations in the different beams and at different altitudes, we were able to compute the phase speed (410 m/s), direction of travel (19° west of south), and horizontal (2500 km) and vertical (290–490 km) wavelengths of the wave. The F layer peak density and height oscillated during this nighttime period, and we consider several mechanisms that might cause these effects. We find that the density oscillation was too large to be caused solely by wave dynamics. We suggest that an influx of ionization from the plasmasphere, and a wave‐induced modulation of the assimilation of this plasma flux into the ambient density, may have been the cause of the observed density increases. During the following morning (February 8) the F layer density was observed to become increasingly large while the layer peak height dropped, and we also consider the cause for this effect.

Ring current development during the great geomagnetic storm of February 1986

The largest geomagnetic storm in recent decades began with a sudden commencement on February 6, 1986, developed slowly over the next two days, and, with a rapid intensification late on February 8, reached a minimum Dst of −312 nT during the first hour of February 9. Initial recovery was rapid, but full recovery took more than a month. In this paper we follow the ring current development during the storm using particle measurements from the charge‐energy‐mass (CHEM) instrument on the Active Magnetospheric Particle Tracer Explorers (AMPTE) CCE spacecraft. We compare the energy content of the ring current ions with that expected from observed Dst values utilizing for the first time composition coverage over nearly the complete ring current energy range (1–310 keV/e). The ring current composition is followed for five days from prestorm quiet time to early recovery phase. Ions of both solar wind and ionospheric origin are important constituents of the storm time ring current. Although H+ carries the majority of the energy during most of the storm, O+ dominates near the storm's maximum phase, with 47% of the energy density compared with 36% in H+. This is in contrast with all of the more moderate storms which occurred during 1984–1985 in which H+ ions contained most of the energy density near storm maximum. The very rapid initial Dst recovery (τ ∼ 9.3 hours) in this storm results largely from the rapid loss of 75‐ to 100‐keV O+ via charge exchange in the inner portion of the ring current (L = 2.5–3.0). Since it has been long observed that initial Dst recovery is much more rapid in great storms than in moderate storms, we suggest that a major (&gt;50%) O+ + N+ ring current component generally exists near the maximum phase of great storms.

The solar origin of geomagnetic storms

A recent study of associations between geomagnetic storms and solar phenomena has found more associations with solar flares than with coronal holes (Garcia and Dryer, 1987). This disagrees with observations of earthbound transients obtained from IPS imaging which showed that nearly all geomagnetically effective disturbances originated from coronal holes at low latitudes. The discrepancy has arisen because the former study failed to take into account the large angular extent of transient eruptions from coronal holes. It is highly probable that the intense geomagnetic storm of February 1986, discussed by Garcia and Dryer, was caused by a low-latitude coronal hole which was present at that time. This answers their question concerning moderately strong flares that apparently cause major storms, while much larger flares often do not; flares may sometimes be associated with eruptions from coronal holes, but only as peripheral events.

The effect of interplanetary parameters as observed in geomagnetic storms in dependence on geomagnetic latitude

The purpose of this study was to determine to what extent the effect of interplanetary parameters is reflected in the separate storms in dependence on geomagnetic latitude. The results were obtained by studying 5 storms of February 1967 and 1968 recorded at 6 observatories between latitude 5.7° and 53.5° with small differences in local time. These results concern the dynamic pressure of the solar wind and the function of the interplanetary electric field, which approximates the plasma injection into the ring current. This is also associated with the decay time of the storm ring. In most cases the dependence of the effect of the investigated parameters on latitude was proved and expressed in terms of quantitative relations with a reasonable degree of correlation. The derived constants were used in a model of time variations of the storm-time geomagnetic field. The storm-time variations, constructed using this model, mostly agree, as regards their main features, with the real variations, whereas differences can be observed in details, namely of a local nature.

Major magnetic storm effects noted

The major magnetic storm of February 8–9, 1986, was possibly the final burst of activity caused by a protracted sequence of one or more large solar flares that occurred daily February 4–7. There is great interest in the entire sequence of events, as the magnetic storm was one of the largest in 40 years. By using satellite and ground‐based near‐real‐time data, the staff of the National Oceanic and Atmospheric Administration Space Environment Services Center (SESC) provided early alerts about this solar activity and its consequences. This was an opportunity to test many of the interactive data bases available through the new SELDADS II (Space Environmental Laboratory Data Acquisition and Display System).

Simultaneous electric field changes in the equatorial electrojet in phase with polar cusp latitude changes during a magnetic storm

The Doppler frequency of the VHF radar signals backscattered from the drifting ionization irregularities in the equatorial electrojet is proportional to the east‐west electric field Ey in the equatorial electrojet. Using the VHF backscatter radar observations at Thumba during the geomagnetic storm of February 16, 1980, it is shown that the decreases and increases of the storm‐time electric fields in the equatorial electrojet are completely in phase with the decreases and increases in the mean latitude of the polar cusp region. This observation has important implications for understanding the magnetosphere‐ionosphere interactions, particularly the effect of the magnetospheric electric fields on the low latitude ionosphere.

The influence of plant cover on surfperch abundance at an offshore temperate reef

At an offshore reef near Santa Barbara, southern California, young-of-year (‘young’) of five surfperch species (Embiotocidae: Embiotoca jacksoni, E. lateralis, Hypsurus caryi, Rhacochilus toxotes, Damalichthys vacca) once thrived in a dense kelp understory of Pterygophora californica and Laminaria farlowii, but disappeared after a severe storm in February, 1980 deforested their habitat. Measurements of fish density and kelp cover made before deforestation indicated that the young surfperch appeared in the spring and disappeared in the fall as cover increased and declined. Adult surfperch and large kelp bass (Paralabrax clathratus), which can eat young but not adult surfperch, remained all year. We tested to see if kelp cover was an essential refuge for the young by pruning back (‘thinning’) kelp blades from one of two transects. The thinning caused a significant redistribution of young which clearly avoided open spaces, but not of adults which are less vulnerable to predation. Measurements of fish density made after the storm-induced deforestation showed that adult surfperch and kelp bass still remained abundant even after the young surfperch were gone. Only after an abrupt reforestation in 1983, more than a year after the present study was terminated, were young once again seen on the reef. Although young surfperch may seek tiny prey living on kelp blades, most lines of evidence indicated that the distribution of the young is more a response to risk of predation. Hence the extent of kelp understory was probably the main determinant of the survival of young surfperch on the reef.

A Diagnostic Analysis of the Presidents' Day Storm Of February 1979

Abstract A diagnostic analysis of the Presidents' Day storm of February 1979 is used to extend and quantify earlier findings of Bosart. The initial growth of cyclonic vorticity in the lower troposphere is driven primarily by convergence along the Carolina coastal front. Rapid cyclone spinup accompanies the approach of a potent midtropospheric short wave trough from the Ohio Valley. An analysis of the vorticity structure discloses that cyclone spinup is enhanced by the~vertical advection of vorticity in the strongly cyclonic in situ vorticity environment along the coast as the upper level trough overspreads the region. Similarly, a downward extension of high semige-strophic potential vorticity air accompanies a tropopause fold to the west of thecyclone and prior to the rapid cyclogenesis stage, confirming a result of Uccellini and others. Semigeostrophic potential vorticity is poorly conserved, however, and there is evidence for a separate region of semigeostrophic potential vorticity growth below 800 mb n...

A preliminary investigation using a Nova Scotia storm surge prediction model

Abstract A test of a storm surge model using the shallow water equations is presented. The model is designed to be run using CMC (Canadian Meteorological Centre) prognostic data. The model incorporates a quadratic bottom friction term and is capable of including advective, topographic and tidal effects. It can simulate a moving land‐sea boundary approximately. The model is applied to the east coast of Nova Scotia for the “Ground Hog Day” storm of February 1976. Meteorological forcing is calculated using subjectively analysed sea‐level pressures. Away from open boundaries, the agreement with observed surge residuals is generally good. However, the results are less satisfactory near the boundaries. CMC meteorological data are found to underestimate the surface wind stress during this period.

Periodicity of Fine Root Growth in Jarrah (Eucalyptus marginata Donn Ex Sm.)

The timing of new surface root growth in jarrah (Eucalyptus marginata) was followed for a 15-month period in the field. The periodicity of new root growth was similar for long roots, non-mycorrhizal and mycorrhizal root clusters. Root growth was initiated during two peak periods in spring (September-October) and following autumn rain (May-June). Little new root activity was recorded in late winter (August) or during summer drought. Rapid root growth occurred within 2 days of a storm (47 mm rain) in February. In addition, short roots formed after very light showers of rain (&lt;5 mm) in late summer. Much of the framework for fine feeder roots was built up after autumn rain. In contrast to new long root growth which was equally spread between spring and late autumn, the majority of new mycorrhizal roots were produced from May to July. Root growth ceased when warm surface soils dried out and commenced when the soils were moist after rain. Much of the new root growth in jarrah occurred when the root pathogen Phytophthora cinnamomi was active in the soil.

The cosmic-ray storm of February 15, 1978

During the Forbush decrease of February 14, 1978 a huge cosmic-ray decrease lasting only ≈10 hours was observed by the neutron monitor stations. A detailed analysis, performed on data of numerous neutron monitors, shows that this event is a bidirectional anisotropy with a cosmic-ray density gradient rising from a plane tilted ≈30° with respect to the Earth equator; the interplanetary magnetic field should be perpendicular to that plane.

Search for the magnetic neutral line in the near-Earth plasma sheet, 3. An extensive study of magnetic field observations at the lunar distance

In this paper we have extended our search for the magnetic neutral line in the magnetotail to the lunar distance on the basis of the Explorer 35 magnetic field observations from July 1967 to December 1970. The sign of the B/sub z/ component is found to be predominantly positive during satellite crossings of the midplane (or the so-called neutral sheet) during the substorm expansive phase. Thus combining the present and the earlier results, we conclude that there is no supporting evidence for the formation of a neutral line within the lunar distance during the expansive phase of most substorms. We also discuss in detail a rare event during the geomagnetic storm of February 2-4, 1969 (Dstapprox.-180 ..gamma..). The magnetic field was observed to be pointing nearly 90/sup 0/ southward with a magnitude of 20-32 ..gamma.. for an extended period.

Observations of neutral composition and related ionospheric variations during a magnetic storm in February 1974

The neutral-atmosphere composition experiment on Atmosphere Explorer C measured N2, O, Ar, and He densities during a magnetic storm at altitudes down to about 160 km. At latitudes above 45 deg N, N2 and Ar densities generally increase during the storm, while He and O densities decrease. Below 45 deg N all densities tend to increase during the storm. The density increases at perigee indicate that density- or temperature-profile changes are taking place below 160 km. The return to prestorm conditions is very slow, demonstrating the integrating effect of the atmospheric response. A recent theoretical model incorporating thermospheric circulation and diffusion effects reproduces the longitudinally averaged data, including latitude trends and the asymmetry about the storm maximum. Comparison with the mass-spectrometer and incoherent-scatter empirical model shows qualitative agreement with latitude trends but not with storm asymmetry, while the earlier J71 model based on total mass density is not in agreement with observed latitudinal trends. A close correlation is found between in situ O/N2 measurements and in situ and ground-based ionosonde measurements of electron density.