No abstract

Compressional oscillations of nearly constant frequency (period ≲ 8 min) were observed from L ≃ 5 to L ≃ 10 near local noon over an interval of almost 3 hours during a dayside radial pass of the ISEE 1 spacecraft on August 12, 1982. The density fluctuations, measured by the electron density experiment, were in phase with the compressional magnetic oscillations measured by the magnetometer. We relate the observations to an analytical model of a global compressional wave reflected at the gradient of the magnetic field and plasma density near the plasmapause and standing in the outer magnetosphere. Qualitative arguments based on the model lead one to expect that conditions in the outer magnetosphere are not normally compatible with the standing wave solution, that when such a solution can be found, only the lowest eigenfrequencies will be present, and that some variation in period with local time may occur.

A detailed study of electron plasma waves observed upstream of the earth’s bow shock and of their relationships to the position of the satellite in the foreshock and to the electron measurements has been carried out. The wave characteristics depend on the position in the electron foreshock: a narrow‐band (a few percent) and intense (a few millivolts per meter) noise is observed at the plasma frequency at the edge of the foreshock while the spectrum widens (Δf/f ≃ 0.3) at the same time as the power decreases (hundreds of microvolts per meter) deeper (a few earth radii) inside the foreshock. Signals below the plasma frequency are also observed. These waves are polarized along the magnetic field, with long wavelengths below and at the plasma frequency and short wavelengths above it. They appear as short bursts, the duration of which depends on the frequency: longer close to the plasma frequency (50 ms), they shorten with increasing separation from the plasma frequency, the usual duration being 15 ms. While the correlation of the wave characteristics with the reflected electrons is good as the satellite moves inside the foreshock, no evolution is found with the distance to the bow shock, neither for the noise nor for the particles. These results are discussed in the frame of various mechanisms which have been proposed to explain these upstream waves but no satisfactory agreement is found with any of them.

Plasma waves associated with the magnetopause, from the magnetosheath to the outer magnetosphere, are examined with an emphasis on high time resolution data and the comparison between measurements by using different antenna systems. An early ISEE crossing of the magnetopause region, including passage through two well‐defined flux transfer events, the magnetopause current layer, and boundary layer plasma, is studied in detail. The waves in these regions are compared and contrasted with the waves in the adjoining magnetosheath and outer magnetosphere. Four types of plasma wave emissions are characteristic of the nominal magnetosheath: (1) a very low frequency continuum, (2) short wavelength spikes, (3) ‘festoon‐shaped’ emissions below about 2 kHz, and (4) ‘lion roars.’ The latter two emissions are well correlated with ultra‐low frequency magnetic field fluctuations. The dominant plasma wave features during flux transfer events are (1) an intense low‐frequency continuum, which includes a substantial electromagnetic component, (2) a dramatic increase in the frequency of occurrence of the spikes, (3) quasi‐periodic electron cyclotron harmonics correlated with ∼1‐Hz magnetic field fluctuations, and (4) enhanced electron plasma oscillations. The plasma wave characteristics in the current layer and in the boundary layer are quite similar to the features in the flux transfer events. Upon entry into the outer magnetosphere, the plasma wave spectra are dominated by intense electromagnetic chorus bursts and electrostatic (n + 1/2)fg− emissions. Wavelength determinations made by comparing the various antenna responses and polarization measurements for the different waves are also presented.

Abstract-Soil Moisture and Ocean Salinity (SMOS) is an Earth Explorer Opportunity Mission from the European SpaceAgency with a launch date in 2007. Its goal is to produce global maps of soil moisture and ocean salinity variables for climatic studies using a new dual-polarization L-band (1400-1427 MHz) radiometer Microwave Imaging Radiometer by Aperture Synthesis (MIRAS). SMOS will have multiangular observation capability and can be optionally operated in full-polarimetric mode. At this frequency the sensitivity of the brightness temperature ( ) to the sea surface salinity (SSS) is low: 0.5 K/psu for a sea surface temperature (SST) of 20 C, decreasing to 0.25 K/psu for a SST of 0 C. Since other variables than SSS influence the signal (sea surface temperature, surface roughness and foam), the accuracy of the SSS measurement will degrade unless these effects are properly accounted for. The main objective of the ESA-sponsored Wind and Salinity Experiment (WISE) field experiments has been the improvement of our understanding of the sea state effects on at different incidence angles and polarizations. This understanding will help to develop and improve sea surface emissivity models to be used in the SMOS SSS retrieval algorithms. This paper summarizes the main results of the WISE field experiments on sea surface emissivity at L-band and its application to a performance study of multiangular sea surface salinity retrieval algorithms. The processing of the data reveals a sensitivity of to wind speed extrapolated at nadir of 0.23-0.25 K/(m/s), increasing at ( ) is found to be correlated with the measured sea surface slope spectra. Peaks in ( ) are due to foam, which has allowed estimates of the foam brightness temperature and, taking into account the fractional foam coverage, the foam impact on the sea surface brightness temperature. It is suspected that a small azimuthal modulation 0.2-0.3 K exists for low to moderate wind speeds. However, much larger values (4-5 K peak-to-peak) were registered during a strong storm, which could be due to increased foam. These sensitivities are satisfactorily compared to numerical models, and multiangular data have been successfully used to retrieve sea surface salinity.

Particle and field data obtained by eight ISEE spacecraft experiments are used to define more precisely the characteristics of the high‐latitude boundary region of the plasma sheet. We find that there is a region immediately adjacent to the high‐latitude plasma sheet boundary whose particle and field characteristics are distinctly different from its neighbors, the lobe and the plasma sheet. This region supports intense ion flows, field‐aligned currents, large amplitude electric fields, and enhanced broad band electrostatic noise. A detailed analysis of events detected on April 19, 1978, shows that the plasma distributions in the region are unstable. For instance, bidirectional field‐aligned electron distributions are observed at nearly all energies (a few electron volts to a few hundred keV). Both the differential energy spectra and the reduced distribution function F(υ∥) = 2π∫υ⊥f(υ∥, υ⊥) dυ⊥ show significant peaks at 100‐400 eV. These peaks comprise electrons coming from the earthward direction. Ions below a few keV are convected in the direction perpendicular to B, whereas the higher energy ions (>30 keV) are field‐aligned and travelling mainly toward the earth. The electric field in the region is intense, spiky, and possibly time varying. The magnetic By component increases dramatically from a few nanoteslas to more than 20 nT, indicating presence of a field‐aligned current. These features are in contrast with the plasma characteristics outside the region. In the adjacent regions (closer to the lobe and the inner plasma sheet regions), the electron distributions are nearly isotropic. Ion flow is virtually at a standstill. The high‐energy ions (>30 keV) are anisotropic and field‐aligned but bidirectional.

[1] In order to determine high-resolution variations of CO 2 distributions in the equatorial Pacific, we have developed seasonal and interannual fCO 2 -SST relationships from shipboard data. The data were gathered onboard NOAA ships from 1992 through 2001. The cruises during the 10-year period included 89 transects of the equatorial Pacific between 95°W and 165°E, and spanned two El Niño events (1992-1994 and 1997-1998). Data were collected during the equatorial warm season (January-June) and cool season (July-December) as well as during all phases of the ENSO cycle, making it possible to examine the interannual and seasonal variability of the fCO 2 -SST relationship. There is a significant difference between the regression lines for El Niño versus non-El Niño data sets. During both non-El Niño and El Niño periods we observed seasonal differences in the fCO 2 -temperature relationship. With respect to the non-El Niño period, the seasonal regression lines have lower root mean square (rms) deviations than the composite non-El Niño regression line, and the slopes are significantly different at the 95% confidence level. The slope for the cool season is less negative than the slope for the warm season, suggesting higher biological productivity occurs during the latter half of the year.

A self‐consistent solution of the equation of wave generation and particle diffusion is obtained for gyroresonant interactions between ELF waves (a few hundred hertz) and medium‐energy electrons (a few tens of kev). A dynamic equilibrium is considered in which new particles are continuously injected and ultimately lost in the atmosphere through diffusion inside the loss cone; meanwhile, waves are generated continuously, but only a fraction of them is reflected by the ionosphere. By an iterative process the wave spectrum can be computed in shape as well as in amplitude; the distribution function of the trapped particles is also obtained. Some of the concepts that were introduced by Kennel and Petschek (1966) are more precisely defined, and attention is drawn to possible misapplications of these concepts. In particular, it is established that the so‐called limiting flux does not have a unique value and that it in fact depends upon the source strength: enhancements by factors of up to 20 can be achieved in very disturbed conditions (Kp ≥ 6). It is also demonstrated that the particle distribution function, in an equilibrium configuration, does not depend on the cold plasma density, a conclusion that is of great geophysical importance. A comparison with experimental data shows a reasonable agreement with the theory and establishes its interest for interpreting ELF hiss and equilibrium particle distributions, at least inside the plasmasphere.