摘要:

In the present paper, ENA energy spectra at the location at the SAC‐B satellite are simulated by using AMPTE/CCE/CHEM ion distributions as originating source, with the purpose of analysing the SACB/ISENA response at different magnetic local times and latitudes. The shape of the ENA spectra simulated along different lines of sight on the equatorial plane is analysed to show that an instantaneous estimate of the global convection electric field will be possible with the ISENA data every few minutes. This unprecedented time resolution for the measurement of such a crucial parameter of the Earths magnetosphere will allow testing of many theories, like tail convection, pressure balance, global circuits, ring‐current shielding,

ISSN:0094-8276    

DOI:10.1029/96GL02925

年代:1996

数据来源: WILEY

摘要:

The Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) has observed small‐ and meso‐scale temperature fluctuations during a special limb‐tracking operation. Analysis of late‐December 1994 data shows that there exist significant radiance fluctuations with horizontal scales of 10's–100's km associated with upper tropospheric convection and the stratospheric polar vortex. Phase coherence and amplitude growth with height are observed, showing the presence of vertically propagating waves. Variance maps generated for the limb‐tracking days further show that the MLS instrument can measure horizontal temperature variations at scales less than 100 km in both limb‐scanning and limb‐tracking ob

ISSN:0094-8276    

DOI:10.1029/96GL02924

年代:1996

数据来源: WILEY

摘要:

Recent auroral sounding rocket data illustrate the relative significance of two transverse acceleration of ion (TAI) mechanisms for initiating nightside auroral ion outflow. First, the new data from this two payload mission show clearly that for lower hybrid solitary wave events, a) these individual events are spatially localized to scales approximately 100 m wide perpendicular toB, and b) the probability of occurrence of the events is greatest at times of maximum VLF wave intensity. Second, ion acceleration by broadband, low frequency electrostatic waves is observed in a 30 km wide region at the poleward edge of the arc. The fluxes from this and other sounding rockets are shown to be consistent with DE‐1 and Freja outflow measurements, indicating that the AMICIST observations show the low altitude, microphysical signatures of nightside auroral outflow from TA

ISSN:0094-8276    

DOI:10.1029/96GL02688

年代:1996

数据来源: WILEY

摘要:

Broadband electric field fluctuations with typical amplitudes of 10–20 mV/m peak‐to‐peak and frequencies from 0 Hz to 3 kHz (BB‐ELF) were observed coincident with a region of ≤200 eV transverse H+acceleration (TAI) near the poleward edge of the pre‐midnight aurora. The coherence and phase velocity of the electric fields were measured using a interferometric antenna array over the frequency range of ≈ 100 Hz to 3 kHz. These electric field fluctuations were found to have the following characteristics: 1) incoherence perpendicular to the geomagnetic field, 2) coherence parallel to the the geomagnetic field, 3) parallel phase velocity (ω/k∥) of 30–35 km/s upwards, 4) 0<|k∥/k⟂|<0.22. We show that these properties are compatible with the emission being electrostatic H+cyclotron (EHC) waves. We also discuss possible generation mechanisms for the waves, and their r

ISSN:0094-8276    

DOI:10.1029/96GL03238

年代:1996

数据来源: WILEY

摘要:

Propagation characteristics of mid‐latitude whistlers, especially whistler duct characteristics, have been investigated based on measurements in August, 1994 at Dunedin, New Zealand(L=2.78) and in August, 1989 at Ceduna, Australia(L=1.93), both during local midnight. Polarization analyses have enabled us to locate whistlers which exited the ionosphere just above the observing station (LDFis defined in this way). The nose extension method was also applied to these whistlers (their Lnis estimated by this method). The following findings have emerged from the analyses; LDF≃ Ln(at Dunedin) and LDF≃ Ln‐0.43(at Ceduna). Our analysis suggests that mid‐latitude ducts are likely to extend down to the ionosphere at L ≈ 2.8. Ray tracing studies for realistic density profiles indicates that a whistler duct terminates at an altitude of about 3,500 ∼ 5,500 km at an L value of ∼1.9 with its enhancement factor being a few percent at least. These results may imply a strong variability of the latitudinal or temporal variations of mid‐latitu

ISSN:0094-8276    

DOI:10.1029/96GL03253

年代:1996

数据来源: WILEY

摘要:

Area‐averaged anomalies of sea surface temperature (SSTA) and rainfall, developed from large scale data sets, have been used to explore the relative importance of Pacific versus Atlantic SST variability for inter‐American (50°S–50°N) climate variability at interannual time scales. SSTA in the tropical Pacific and tropical North Atlantic are comparably related to rainfall north of 15°S, with clear associations distributed between the southeastern United States (US) in the north and northern South America in the south. Although NINO3 explains 25% of the variance of the North Atlantic SSTA index, the rainfall correlations with North Atlantic SSTA are for the most part opposite in sign to those with NINO3. Hence, a significant part of the Atlantic SSTA probably has a direct association with rainfall, rather than being merely an indirect proxy for Pacific ENSO linkages. In contrast to the North Atlantic, South Atlantic SSTA appear to be only related to rainfall in northeast (NE) Brazil. The entire region between Venezuela and NE Brazil appears to be sensitive to both the ITCZ and to antisymmetric configurations of SSTA across the ITCZ, in a manner consistent with the relationships between SST, surface wind and surface wind divergence fields, and with previous

ISSN:0094-8276    

DOI:10.1029/96GL03231

年代:1996

数据来源: WILEY

摘要:

An argument based on general principles and minimal development is presented to establish the role of nonlinearity in producing the observed saturation of gravity‐wave spectra in the middle atmosphere. The complementary role of instability of the nonlinear spectrum is discussed. Earlier models of nonlinear saturation are reviewed in the context thus provide

ISSN:0094-8276    

DOI:10.1029/96GL03236

年代:1996

数据来源: WILEY

摘要:

In recent studies on the photolysis of ozone the triplet channel has been given much attention as a possible extra ozone source. The vibrationally excited oxygen molecules produced can either be quenched to heat the atmosphere or photolysed at longer wavelengths than normally possible for O2. The latter potentially lowers the fraction of solar energy that is converted to heat. Lack of experimental data to accurately estimate this fraction and the relatively small contribution to the total heating has been used to justify neglect of this effect. However, recent information on the quantum yield of excited oxygen as function of wavelength from ozone dissociation makes it possible to calculate the atmospheric heating efficiency in the ozone triplet channel in a more quantitative fashion. With the new quantum yield data the atmospheric heating efficiency in the triplet channel deviates from unity only above 80 km where the magnitude of the deviation is strongly dependent on the quantum yield. However, the large yield into the singlet channel masks any deviations from unit in the triplet channel. Therefore the current results indicate that previous work, which assumed unity heating efficiency for the triplet channel in the whole altitude range, is within 4% of a detailed calculation. Below 80 km the current results are consistent with previous work.

ISSN:0094-8276    

DOI:10.1029/96GL03151

年代:1996

数据来源: WILEY

摘要:

Lidar observations of stratospheric ozone made at Eureka (80.0°N, 86.42°W) during the 95/96 winter show substantial declines in ozone mixing ratios. Reductions in ozone levels of up to 40% between the 410 K and 580 K isentropic levels were observed between mid‐January and mid‐March. The correlation of the ozone data with potential vorticity and concurrent lidar observations of stratospheric aerosol is consistent with the claim that significant chemical depletion did

ISSN:0094-8276    

DOI:10.1029/96GL03230

年代:1996

数据来源: WILEY

摘要:

Estimates from two 2‐D (latitude ‐ height) chemical transport models of changes in tropospheric ozone concentrations since pre‐industrial times were used to calculate the radiative forcing due to these changes. The ozone changes are from Cambridge (CAMB) and the U. K. Meteorological Office (UKMO) models. The global and annual mean forcing using the UKMO changes was 0.3 Wm−2and was 0.5 Wm−2using the CAMB changes. The UKMO ozone changes are typically 60% of those from CAMB and this entirely accounts for the different forcing. Although the uncertainty is large, the calculations continue to support the case that tropospheric ozone changes make a substantial contribution (about 15%) to the total greenhouse gas radiative forcing. It is also shown that ignoring cloud and the effects of stratospheric adjustment in the radiative forcing calculations leads to an over‐estimation of the forcing by about 66%, for the glo

ISSN:0094-8276    

DOI:10.1029/96GL03277

年代:1996

数据来源: WILEY