摘要:

Measurements of suprathermal electron fluxes in the solar wind indicate that field lines within coronal mass ejections, CMEs, near and beyond 1 AU are normally connected to the Sun at both ends. However, on occasion some field lines embedded deep within CMEs appear to be connected to the Sun at only one end. Here we propose an explanation for how such field lines arise in terms of 3‐dimensional reconnection close to the Sun. Such reconnection also provides a natural explanation for the flux rope topology characteristic of many CMEs as well as the coronal loops formed during long‐duration, solar soft X‐ray events. Our consideration of the field topologies resulting from 3‐dimensional reconnection indicates that field lines within and near CMEs may on occasion be connected to the outer heliosphere at bo

ISSN:0094-8276    

DOI:10.1029/95GL00270

年代:1995

数据来源: WILEY

摘要:

We investigate the ionization of interstellar hydrogen and helium due to electron impact by shock‐heated electrons. Taking the electron distributions measured at four interplanetary shocks at 1 AU, we show that the electrons in the downstream region of strong shocks can ionize interstellar atoms at rates matching or exceeding the nominal photoionization or charge‐exchange rates. We suggest that this process may explain some puzzling observations of interstellar pickup ions made by the Ulysses spacecr

ISSN:0094-8276    

DOI:10.1029/95GL00703

年代:1995

数据来源: WILEY

摘要:

The results of observations of spatial distribution and dynamics of trapped He fluxes with the energy 3.2‐9.2MeV/nucobtained by low altitude Japanese OHZORA satellite are reported. Transient trapped He fluxes associated with solar and magnetospheric activity were observed at low altitudes in the region ofL=2.0‐3.0. Possible sources of the fluxes including remnants of solar particle population trapped during substorms, acceleration of hot plasma from the outer magnetosphere, and pitch‐angle scattering from the top of the magnetic field line are disc

ISSN:0094-8276    

DOI:10.1029/94GL03053

年代:1995

数据来源: WILEY

摘要:

The seasonal and UT variation of mesoscale structures (10 km – 100 m) in the central polar cap has been obtained from an analysis of 250‐MHz intensity scintillation observations made at Thule, Greenland. It has been established earlier [Su. Basu et al., 1990] that mesoscale structures causing scintillations of satellite signals may develop at the edges of macroscale structures (several hundred km) such as discrete polar cap plasma density enhancements or patches through the gradient drift instability process. As such, we examined the seasonal and UT variation of polar cap patches simulated by using the USU Time Dependent Ionospheric Model (TDIM) under conditions of southward Bz. A fairly remarkable similarity is found between the scintillation observations and the model predictions of patch occurrence. For instance, both the patch and scintillation occurrences are minimized during the winter solstice (northern hemisphere) between 0800–1200 UT while also having their largest seasonal intensity between 2000–2400 UT. Little UT dependence of patches and scintillations is seen at equinox with high intensity being observed throughout the day, while during local summer the intensity of macroscale patches and mesoscale irregularities are found to be a minimum at all UT. These results indicate that macroscale features in the polar cap are routinely associated with plasma instabilities giving rise to smaller scale structures and that the specific patch formation mechanism assumed in the simulation is consistent with the observations. This ability to bridge between macroscale modeling and mesoscale observations provides a natural framework for the modeling of mesoscale structures themselves. This mesoscale modeling, in turn, can be utilized in a variety of radar and communication systems applications in the polar

ISSN:0094-8276    

DOI:10.1029/95GL00467

年代:1995

数据来源: WILEY

摘要:

As there are a significant number of observed onset conditions for the post‐sunset equatorial spreadFthat are not evidently associated with the required (5%) seed perturbation as assumed by the earlier simulation studies, an investigation is carried out with different seeding conditions for the evolution of plasma bubbles in the equatorialFregion by means of a nonlinear numerical simulation model. The present investigation reveals that even an order of magnitude less perturbation (0.5%) than the earlier belief, grows into a bubble provided the nonlinear effects of other agencies such as the vertical wind and the electric field, in addition to gravity are taken into account. It is suggested that the above amplitude of the initial perturbation in plasma density can be generated through electrodynamical effects by the observed fluctuations in the electric field

ISSN:0094-8276    

DOI:10.1029/95GL00813

年代:1995

数据来源: WILEY

摘要:

The BLACKBEARD payload aboard the ALEXIS satellite has been making broadband observations in the VHF band of the radio spectrum. Since November of 1993 several hundred unusual signals have been recorded. The peculiar nature of these bursts of radio noise is that they have a duration of approximately 10 µsec, are typically 20 to 40 dB brighter than the average background, and occur in pairs separated by approximately 50 µsec. We have dubbed these emissions TransIonospheric Pulse Pairs, or TIPP events. We do not know what the source of these emissions is, but the dispersion of these signals is consistent with an origin at or near the earth's surface. The satellite field of view and time of day when TIPP events are generally detected are consistent with regions of thunderstorm activity such as south‐central Africa or Indone

ISSN:0094-8276    

DOI:10.1029/95GL00432

年代:1995

数据来源: WILEY

摘要:

Recent updates and extensions to a steady‐state two‐dimensional linearized model of global‐scale atmospheric waves have facilitated improved calculations of the subset of those waves which are subharmonics of a solar day and propagate with the apparent motion of the sun. The model improvements are briefly described and some updated predictions of the migrating solar diurnal component are highlighted. The latter represent the first numerical modeling effort to examine the seasonal variability of the migrating diurnal harmonic as it propagates into the mesosphere and lower thermos

ISSN:0094-8276    

DOI:10.1029/95GL00783

年代:1995

数据来源: WILEY

摘要:

We have reviewed the most recent results on acetylene absorption in the weak A‐X band system (features longward of 185 nm). Then, using acetone absorption measurements in the 185–200 nm range together with saturated vapor pressure studies of acetone, we are able to resolve discrepancies noted by several authors for some A‐X

ISSN:0094-8276    

DOI:10.1029/95GL00706

年代:1995

数据来源: WILEY

摘要:

Semidiurnal solar tides in the mid‐latitude troposphere are investigated using harmonic analysis of 404 MHz radar profiler wind data obtained from a wide longitude zone in the U.S. The tides are apparent above a 1000‐m‐deep surface layer and increase in amplitude with height, attaining speeds of 0.5–0.7 m/s at 5–7 km. Observed wind characteristics agree well with tidal characteristics obtained with a dynamical model driven by observed global semidiurnal horizontal pressure

ISSN:0094-8276    

DOI:10.1029/95GL00816

年代:1995

数据来源: WILEY

摘要:

The long‐term time series of global ozone from the Nimbus‐7 SBUV (Nov. 1978–June 1990) are extended through June 1994 by using measurements from the NOAA‐11 SBUV/2. The data sets are merged based upon comparisons during the 18‐month overlap period in which both instruments were operational. During this period, the average offset between the two time series is less than 2% in total ozone, and less than 6% in Umkehr layers 1–10. A linear‐regression trend model is applied to the extended time series to calculate updated trends as a function of latitude and altitude. Trends through June 1994 are 1.5‐2% per decade less negative than through June 1990 in the tropical middle stratosphere (35–40 km) and in the upper stratosphere (45–50 km) at mid‐latitudes. In the lower stratosphere, the trends are nearly 1.5% per decade more negative in the southern hemisphere tropical regions to 25°S, but remain relatively unchanged elsewhere. The seasonal structure of the total ozone trends is similar to past trend study results, but the magnitude of the seasonal trend can vary by 2% per decade depending on the length of the time series. Both TOMS (through April 1993) and SBUV total ozone time series show small negative trends in the equatorial region, though they are not statistically signif

ISSN:0094-8276    

DOI:10.1029/95GL00605

年代:1995

数据来源: WILEY