摘要:

Interaction between the lower thermosphere, at 40°N, and the stratosphere has been found during stratospheric warming events. This interaction shows a temperature decrease of the lower thermosphere of about 10°K (with a 95% confidence interval from 4.2°K to 17°K). Cooling already occurs by the time of peak stratospheric warming; however, maximum cooling appears nearly one lunation later. The measurements show the average magnitude of the cooling effect to be independent of solar activity, magnetic activity, and other long‐term secular variations to which the temperatures in the lower thermosphere are sensitive and to be independent of a 34° longitude separation in observing sites. The results indicate that the magnitude of the cooling effect may be dependent on the time of occurrence of the stratospheric warming during the winter; however, there are not enough measurements to test this contention

ISSN:0148-0227    

DOI:10.1029/JA082i016p02127

年代:1977

数据来源: WILEY

摘要:

This numerical study of the global distribution of helium in the terrestrial thermosphere is based on the extension of a three‐dimensional single‐fluid numerical model of the thermosphere previously developed by the authors to treat the dynamics of a minor gas imbedded in a background gas made up of N2, O2, and O. The Cira (1972) model of the upper atmosphere, based on satellite drag data, is used to specify the background gas density and temperature as functions of altitude, latitude, and local time for a given day of the year. Specific emphasis is placed on a study of the helium distribution at solstice, i.e., the ‘winter helium bulge.’ Effects of solar activity, eddy diffusion, and exospheric transport on the global distribution of helium are investigated. The model reproduces the general features of the winter helium bulge, including the variation of its amplitude with solar activity, as determined by comparison of data from several recent satellite‐borne mass spec

ISSN:0148-0227    

DOI:10.1029/JA082i016p02132

年代:1977

数据来源: WILEY

摘要:

Measurements of neutral N2density from mass spectrometers on five satellites (AE‐B, Ogo 6, San Marco 3, Aeros A, and AE‐C) and neutral temperatures inferred from incoherent scatter measurements at four ground stations (Arecibo, Jicamarca, Millstone Hill, and St. Santin) have been combined to produce a model of thermospheric neutral temperatures and N2densities similar to the Ogo 6 empirical model. The satellite‐ and ground‐based measurements provide unique and complementary information on the structure of the thermosphere. Incoherent scatter data have good local time coverage at the station locations and provide data for studies of long‐term trends. Measurements from satellites provide information at different altitudes, latitudes, longitudes, solar activities, and seasons. The overall data set covers the time period from the end of 1965 to mid‐1975. The global average temperature from the new model for anF10.7of 150 is 1041°K or 56°K lower than that from the Ogo 6 model. The annual temperature variation is about two‐thirds that of the Ogo 6 model, but variations in lower bound density (inferred from low‐altitude AE‐C data) and lower bound temperature (from incoherent scatter data) result in annual density variations at high altitude very similar to those in the Ogo 6 model. Diurnal and semidiurnal variations in lower bound density and temperature gradient parameters are also introduced. Model diurnal exospheric temperature variations reflect the observed changes with season seen in incoherent scatter measurements. Data used in the model cover a wide range of solar activities (meanF10.7of 75–180), and the annual and diurnal temperature amplitudes are found to increase with solar activity at twice the rate of the mean temperature. The model fits moderate magnetic activity better than the Ogo 6 model but does not include observed longitude variations. The overall good agreement of the individual data sets with the model confirms the basic consistency of the various measurements taken in d

ISSN:0148-0227    

DOI:10.1029/JA082i016p02139

年代:1977

数据来源: WILEY

摘要:

Measurements of O, He, and Ar from neutral gas mass spectrometers on four satellites (Ogo 6, San Marco 3, Aeros A, and AE‐C) and inferred O2and H densities from an ion mass spectrometer on AE‐C have been combined with a neutral temperature and N2density model, based on data from these four satellites and four incoherent scatter stations, to produce a global model of thermospheric composition in terms of inferred variations at 120 km. The data coverage is significantly improved over that of the similar Ogo 6 model in terms of altitude, seasonal, and solar parameters, and the usefulness is expanded by the inclusion of additional gas species. The overall data set covers the time period from mid‐1969 to mid‐1975. The seasonal He density variation is double that of the Ogo 6 model on average, with maximum variation in the northern hemisphere. Ar variations at 120 km tend to be in phase with temperature variations and inverse to the He, O, and H var

ISSN:0148-0227    

DOI:10.1029/JA082i016p02148

年代:1977

数据来源: WILEY

摘要:

The Pioneer 10 and 11 missions to Jupiter and beyond have provided the first opportunity to observe solar flare accelerated particles at distances of several astronomical units from the sun. The intensity‐time profiles out to at least 6 AU are consistent with mainly diffusive interplanetary propagation. No obvious effects of a free escape boundary have been observed, which implies that the outer boundary of the diffusion region is beyond 10 AU. Four solar particle events are discussed in detail. These are events during which azimuthal propagation and corotation effects played a relatively minor role at least until the time of maximum intensity. Their intensity‐time profiles, which were observed simultaneously at two or three well‐separated radial positions (with Imp 6 or Imp 8 at 1 AU and with Pioneer 10 and/or Pioneer 11 at 2.7–6.1 AU), are used to study the radial transport of energetic particles in interplanetary space. The events are interpreted in terms of a spherically symmetric propagation model (which is also appropriate within the flux tube from the coronal release site even ifK∥≫K⊥) which includes the effects of diffusion, convection, and adiabatic deceleration and which assumes that the particles are impulsively injected at the sun. If the effective radial diffusion coefficient is assumed to have the formKr=Kr(1 AU)(r/re)b, the average value of the radial indexbis found to be 0.4 ± 0.2. The average radial diffusion coefficient at 1 AU for 11‐ to 20‐MeV protons isKr(1 AU) = (1.7 ± 0.2) × 1021cm²/s; for 30‐ to 67‐MeV protons,Kr(1 AU) = (2.9 ± 0.2) × 1021cm²/s; and for 1‐ to 2‐MeV electrons,Kr(1 AU) = (4–9) × 1021cm²/s, all for the period 1972–1974. The corresponding radial mean free paths at 1 AU are λr(1 AU) = 0.065 ± 0.010 AU independent of energy for protons from 11 to 67 MeV and λr(1 AU) = 0.03–0.06 AU for the 1‐ to 2‐MeV electrons. The measured solar wind speeds are used to estimate the solar connection longitude of each spacecraft in order to interpret better the observed intensity‐time profiles in terms of radial propagation and corotation. It is found that when the calculated solar connection longitude remains nearly constant during an event (a ‘dwell’ region), a period during which corotation effects are minimized, the model intensity‐time prediction tends to agree with that observed even in the decay phase of the event. The maximum intensity is found to decrease with radial distance asr−3tor−4, which is consistent with the cross‐sectional area of the flux tube containing the particles

ISSN:0148-0227    

DOI:10.1029/JA082i016p02157

年代:1977

数据来源: WILEY

摘要:

A new approach to determining the solar progenitor of transient cosmic ray intensity variations has revealed that in a statistical sense, solar flares, heretofore regarded as the predominant source of the modulation, actually do not precede the reduction in flux observed at earth. Superposed epoch analysis of the cosmic ray data with respect to the time of occurrence of all 379 solar flares of importance (Imp) ≥ 2 observed during solar cycle 20 (1964–1974 inclusive) shows that the onset of a decrease in the composite nucleonic intensity at polar stations occurs prior to the zero day (i.e., time of the flare) well before the arrival in the vicinity of earth of the associated solar plasma. The statistical significance of this result is confirmed by comparing the pooled variance determined from Chree analysis of an equal number of random epochs with that of the curve representing the flare epochs. Subdivision of the latter into three groups according to the heliographic longitude of the flares shows that whereas eastern flares might be associated with cosmic ray decreases, central (30° to −30°) and western flares cannot be thus related. A similar analysis of all flares of Imp ≥ 2 that occurred in a selected set of 24 extraordinary flare‐rich active centers during 1964–1974 confirms these results and shows that the observed cosmic ray intensity decrease is, in fact, associated with the central meridian passage (±1 day) of the active regions. Thus earlier conclusions concerning relationships between the heliolongitude of flares and their apparent effectiveness in producing Forbush decreases require reevaluation. The specific feature associated with solar active centers that is actually the principal source of transient modulations remains to

ISSN:0148-0227    

DOI:10.1029/JA082i016p02170

年代:1977

数据来源: WILEY

摘要:

Coronal magnetic field structure is investigated by using solar and interplanetary magnetic polarity measurements and by using observations of solar wind plasma and energetic particles during the first 8 months of 1965. When it is compared by using all data available during this period, interplanetary polarity (mapped back to the high corona by using observed solar wind velocities) correlates best with mid‐latitude solar polarity. However, when it is compared at only those times when energetic particles were present in the interplanetary medium and again at times of fast solar wind, the best correlation is with equatorial solar polarity. From these results we infer that energetic particles and fast solar wind escape preferentially from equatorial coronal magnetic structures which are open, while the more usual equatorial structures at this time are close

ISSN:0148-0227    

DOI:10.1029/JA082i016p02175

年代:1977

数据来源: WILEY

摘要:

Data supplied by the spacecraft Explorer 33, 34, and 35 and Pioneer 6 and 7 are used to perform a statistical study of the north‐south component of the solar wind velocity. No evidence has been found for significant solar wind motions diverging away from the solar equator, such as those predicted by some models of the expanding corona. The north‐south velocity appears to be strongly correlated with other solar wind parameters (density, bulk speed, proton thermal pressure); these relationships are interpreted in terms of high‐ and low‐speed stream interactions, leading to the suggestion that most of the high‐velocity streams in the period considered originated in the more active northern solar hemisphere. Although in general the meridional flow of the solar wind does not seem to be simply related to the pattern of the interplanetary magnetic field lines, a connection appears to exist in regions where the plasma is compressed, the lines of force (as well as the stream lines) being pushed away from the Parker sp

ISSN:0148-0227    

DOI:10.1029/JA082i016p02187

年代:1977

数据来源: WILEY

摘要:

Non‐LTE (local thermal equilibrium) calculated vibrational temperatures of CO2and N2in the altitudezregion 40

ISSN:0148-0227    

DOI:10.1029/JA082i016p02195

年代:1977

数据来源: WILEY

摘要:

In order to calculate accurately the non‐LTE (local thermal equilibrium) CO2ν34.3‐µm radiance resulting from emission at altitudes greater than about 50 km it is necessary to consider (1) the near‐resonant υυ coupling between N2and the CO2ν3states, N2+ CO2(ν1ν2ν3) ⇄ N2≠+ CO2(ν1ν2ν3‐ 1), and (2) the radiative transport altitude coupling in a given ν3band, i.e., CO2(z, ν1ν2ν3) → CO2(z,ν1ν2ν3‐ 1) +hν3;hν3propagates from altitudezto altitudez′ and is absorbed,hν3+ CO2(z′, ν1ν2ν3‐ 1) → CO2(z′, ν1ν2ν3). Quenching and excitation by thermal processes must also be accounted for. We utilize a set of 11 CO2ν3bands that are sufficiently complete for an accurate description of the problem. The12C16O2001 ⇄ 000 band is by far the strongest of these bands, but errors as large as a factor of 3 in the magnitude and the timing of the CO24.3‐µm radiance may be made if the weak bands are not included in the calculation. We apply the theory for the analysis of rocket‐measured auroral 4.3‐µm zenith radiance data that have been reported in the literature (Stair et al., 1975). We also point out that the theory is generally applicable for any

ISSN:0148-0227    

DOI:10.1029/JA082i016p02203

年代:1977

数据来源: WILEY