摘要:

The observations obtained during the IMS from the IGS magnetometer chain extending from Cambridge, England, to Tromso, Norway are used to study the time rate of change of the magnetic field at subauroral latitudes at the time of interplanetary shock passages. The time rate of change of the H component maximizes in the high latitude dayside sector. For these typical interplanetary shocks, the dayside value of time rate of change can be as high as ∼ 3 nT/sec at Tromso and ∼ 1 nT/sec at York. The time rate of change in the dayside roughly depends on the change of square root of solar wind dynamic pressure. The largest of these time rates of change are similar to but slightly smaller than those known to cause disruptive disturbances in power distribution and communication systems. Thus, the daytime effects of sudden impulses may be equal to or greater than the nighttime effects associated with substorms as measured by their impact on terrestrial syst

ISSN:0094-8276    

DOI:10.1029/92GL03012

年代:1993

数据来源: WILEY

摘要:

The annual average solar daily variations of the eastward component of the geomagnetic field, Y, at the equatorial stations, Kodaikanal and Huancayo indicate an increase on disturbed than on quiet days. With increasing daily mean geomagnetic activity index Ci, there is a systematic increase of daily mean value of Y and the systematic decrease of the daily mean value of H, (northward component) at both the stations. The storm‐time variations of the Y field are in opposite to the corresponding variations of the H field at both the stations. It is suggested that with increasing geomagnetic activity, the development of equatorial ring current is associated with corresponding increase of meridional currents at low latitude

ISSN:0094-8276    

DOI:10.1029/92GL00632

年代:1993

数据来源: WILEY

摘要:

In a laboratory simulation experiment of the earth's magnetosphere, an evidence of the existence of an earthward electric field is shown in the equatorial current sheet. The earthward electric field may be generated as a result of Hall electric field generation in the current sheet. A simple theoretical model for the existence of an earthward electric field is presented. The ions in the current sheet are accelerated by this earthward electric field, which then penetrate into the near earth dipole magnetic field. At the end of the current sheet near the earth, these ions are accumulated due to the difference of the inertia between ions and electrons. The polarization of charges reverses the electric field from earthward to tailward at this region. The experimental results have shown two directional electric fields along x‐axis in the current sheet. The earthward direction of the electric field is due to the dawn‐dusk current sheet carried by electrons. These experimental results prove the theoretical prediction. A discussion of the application of this result to the real magnetotail physics is also presen

ISSN:0094-8276    

DOI:10.1029/92GL02492

年代:1993

数据来源: WILEY

摘要:

Low frequency (ω100 mV/m) Alfvén waves occur in the auroral zone. Such waves have a ponderomotive effect, on both ions and electrons. In the region between the large wave field and the ionosphere, the ponderomotive force accelerates electrons downward and ions upward, which produces an ambipolar electric field. The combined effect is to produce a differential acceleration between O+and H+with the O+accelerated more out of the ionosphere. The typical resulting energization for O+is tens of eV, which is sufficient for the ions to escape the ionosphere. We demonstrate this by means of analysis and test‐particle calcula

ISSN:0094-8276    

DOI:10.1029/92GL03011

年代:1993

数据来源: WILEY

摘要:

There has been concern in the past that spaced antenna radar measurements of energy dissipation rates in the Mesosphere using broad beam arrays may be contaminated by the effects of atmospheric gravity waves. To investigate this possibility, a 1.98 MHz Doppler radar operated by the University of Adelaide was used in two separate configurations; a narrow vertical beam (4.5° half power half width) and 3 smaller spaced antenna systems with broad beams (20° half power half width) were used to simultaneously measure energy dissipation rates in the height region 80 to 100km. The 3 broad beams were also used to determine winds by the spaced antenna method. Although extraction of the energy dissipation rate parameter is a difficult process, temporally and spatially coincident data were obtained enabling some important comparisons to be made. Three years of such data were analysed and the following results noted: (1) the mean energy dissipation rates as measured by the two radars are comparable, (2) the variance of the data as measured by the Doppler radar is larger than that measured by the spaced antenna radar, (3) The spaced antenna radar does not generally over‐estimate energy dissipation rates at moderate and large values, but when turbulence is very weak, it may do so. The degree of over‐estimation is not as serious as has been inferred in the past. However, there is considerable scatter in the short term ratio of measurements using the two methods, which emphasizes the large degree of spatial variability of turbulence strengths in the middle atmos

ISSN:0094-8276    

DOI:10.1029/92GL01116

年代:1993

数据来源: WILEY

摘要:

One of the mechanisms that has been proposed to explain the phenomenon of sudden sodium layers (SSLs) in the upper atmosphere is dissociative attachment of electrons to sodium compounds such as NaHCO3and NaCO3. In this study,abinitiocalculations have been used to estimate the reaction enthalpies (ΔH°0(NaX + e−→ Na + X−)) for NaHCO3and NaCO3, which are found to be 72 ± 20 (0.75) and 21 ± 30 (0.22) kJmol−1(eV), respectively. NaHCO3is then shown to be relatively stable above the mesopause. This property, together with its rather small threshold for dissociative electron attachment, makes NaHCO3a possible source of SSLs under certain

ISSN:0094-8276    

DOI:10.1029/92GL03015

年代:1993

数据来源: WILEY

摘要:

HOx(OH+HO2) and NOx(NO+NO2) radicals play a key role in controlling global ozone. However, several atmospheric measurements of these species are larger than current model calculations suggest. The oxidation of H2and N2O by the second electronically excited state of oxygen, O2(b1Σg+), is theoretically possible and proposed here as an atmospheric source of these radicals. If only 1% of the quenching of O2(b1Σg+) by H2and N2O results in the proposed oxidation products (OH and NO+NO2), then model calculations predict a significant production of these radicals in exactly those regions of the atmosphere were current models seem to fai

ISSN:0094-8276    

DOI:10.1029/92GL03014

年代:1993

数据来源: WILEY

摘要:

Total Ozone Mapping Spectrometer (TOMS) measurements of equatorial total ozone following the eruption of Mt. Pinatubo show a decrease of up to 6% over climatology. Ozone losses begin approximately a month following the eruption, consistent with the time required for the SO2to convert to sulfuric acid aerosol. The thick aerosol layer interferes with the TOMS retrieval, but this interference is small and easily accounted for in the retrieval. Ozone values remain below climatology until December, 1991. Ozonesonde data from Natal, Brazil taken before and two months after the eruption support TOMS observations of ozone loss. These sondes show that the ozone loss region is confined to a 2–3 km thick layer between 24 and 28 k

ISSN:0094-8276    

DOI:10.1029/92GL02637

年代:1993

数据来源: WILEY

摘要:

The impact of the Mt. Pinatubo eruptions on the total column ozone measured from the Nimbus 7 TOMS and the NOAA ‐11 SBUV/2 spectrometers has been studied. The ozone anomalies inferred from the two instruments agree within 1–2 % in the presence of large volcanic clouds produced by Pinatubo. The Pinatubo eruptions took place on June 15–16, 1991 during the easterly phase of the quasi biennial oscillations (QBO) and as such present a different dynamical scenario for the changes in stratospheric ozone compared to the El Chichon eruptions which took place during the westerly phase of the QBO. Within a few months after the eruptions, the total column ozone decreased by 5–6 % in the tropics, 3 to 4 % at mid‐latitudes and 6–9 % at high latitudes in the northern hemisphere. However, after the effects of QBO and interannual variability are taken into account, the decrease in the column ozone attributed to volcanic eruptions at these latitudes may not be more than 2–4 % – a conclusion in general agreement with a similar study of the El Chichon effects on the stratospheric ozone. The most noticeable effect of the Pinatubo eruptions, as observed during the El Chichon period, is the breakdown of the phase relation between ozone and temperature. This is attributed to additional heating in the lower stratosphere caused by vo

ISSN:0094-8276    

DOI:10.1029/92GL03013

年代:1993

数据来源: WILEY

摘要:

Statistically significant correlations are demonstrated between annual mean column ozone data collected at mid‐latitude sites [Kerr, 1991] and mean annual and winter sea ice extents east of Greenland and in the Barents and Kara Seas. These results are discussed with reference to the locations of the correlated parameters relative to the “Basic Pattern” of stratosphere‐solar flux correlations [Labitzke and van Loon, 1992]. Possibilities for underlying linkage mechanisms are considered and related to recent decreasing hemispheric ozone level

ISSN:0094-8276    

DOI:10.1029/92GL03005

年代:1993

数据来源: WILEY