The upper atmosphere and ionosphere of Mars

The topics discussed include the following: the dynamic atmosphere of Mars; possible similarities with Earth and Venus; the atmosphere and ionosphere of Mars; solar wind interactions; future approved missions; and possible future mission

Kilometer‐sized waves in electron density in the Venusian nightside ionosphere

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95281/1/grl7045.pd

To what extent is mass loading responsible for the Venus bowshock precursor?

Significant ion and electron flux enhancements immediately upstream of the Venus bow shock were observed by the Electron Temperature Probe on the Pioneer Venus Orbiter. It is shown that mass loading of the solar wind by oxygen ions accounts for only about 10 percent of the observed effect

Solar cycle variations of electron density and temperature in the Venusian nightside ionosphere

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95478/1/grl7104.pd

Use of Langmuir probes in non-Maxwellian space plasmas

Disturbance of the Maxwellian plasma may occur in the vicinity of a spacecraft due to photoemission, interactions between the spacecraft and thermospheric gases, or electron emissions from other devices on the spacecraft. Significant non-Maxwellian plasma distributions may also occur in nature as a mixture of ionospheric and magnetospheric plasmas or secondaries produced by photoionization in the thermosphere or auroral precipitation. The general formulas for current collection (volt–ampere curves) by planar, cylindrical, and spherical Langmuir probes in isotropic and anisotropic non-Maxwellian plasmas are examined. Examples are given of how one may identify and remove the non-Maxwellian components in the Langmuir probe current to permit the ionospheric parameters to be determined. Theoretical volt–ampere curves presented for typical examples of non-Maxwellian distributions include: two-temperature plasmas and a thermal plasma with an energetic electron beam. If the nonionospheric electrons are Maxwellian at a temperature distinct from that of the ionosphere electrons, the volt–ampere curves can be fitted directly to obtain the temperatures and densities of both electron components without resorting to techniques that attempt to derive the plasma distribution from the current by taking derivatives. For an arbitrary isotropic distribution, the current for retarded particles is shown to be identical for the three geometries. For anisotropic distributions, the three probe geometries are not equally suited for measuring the ionospheric electron temperature and density or for determining the distribution function in the presence of non-Maxwellian background electrons. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70117/2/RSINAK-70-7-3015-1.pd

Empirical models of the latitudinal variations of Te and Ne in the ionosphere at solar maximum

Global spectral models of electron temperature (Te) and density (Ne) were produced earlier using Dynamics Explorer-2 (DE-2) Langmuir probe measurements made between 1981 and 1983. The models were derived for the fixed altitudes of 300, 500, and 850 km. The variables in those models included spatial structure (geomagnetic latitude and longitude) and temporal variations (local time, season, UT, F10.7, and kp). Unfortunately, the DE-2 data base is not adequate to fully define all of these variables because of the eccentricity of the orbit, the slow evolution of the orbit, and the brevity of the mission (19 months). Legendre polynomials beyond order 5 could not be well enough defined to resolve small scale structures like the auroral oval, the midlatitude trough, and the equatorial anomaly, though these feature are clearly evident in the profiles from individual orbits. In the present work we take a different approach by modelling only the latitudinal variations observed in narrow altitude and local time bands and using measurements obtained during intervals short compared to a season. This approach allows the data to accurately define latitudinal terms up to 17 th order. To illustrate this improved latitudinal resolution, selected models of Te and Ne at 500 km are compared with latitude profiles from the earlier global models and with the DE-2 measurements for the same local times and altitudes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29564/1/0000652.pd

Energetics of the dayside ionosphere of Venus

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94981/1/grl6860.pd

Pioneer Venus Orbiter Measurements of Solar EUV Flux During Solar Cycles 21 and 22

The Pioneer Venus Orbiter (PVO) had on board the electron temperature probe experiment which measured temperature and concentration of electrons in the ionosphere of Venus. When the probe was outside the Venus ionosphere and was in the solar wind, the probe current was entirely due to solar photons striking the probe surface. This probe thus measured integrated solar EUV flux (Ipe) over a 13-year period from January 1979 to December 1991, thereby covering the declining phase of solar cycle 21 and the rising phase of solar cycle 22. In this paper, we examine the behavior of Ipe translated to the solar longitude of Earth (to be called EIpe) during the two solar cycles. We find that total EUV flux changed by about 60% during solar cycle 21 and by about 100% in solar cycle 22. We also compare this flux with other solar activity indicators such as F_10.7 , Lα, and the solar magnetic field. We find that while the daily values of EIpe are highly correlated with F_10.7 (correlation coefficient 0.87), there is a large scatter in EIpe for any value of this Earth-based index. A comparison of EIpe with SME and UARS SOLSTICE Lα measurements taken during the same period shows that EIpe tracks Lα quite faithfully with a correlation coefficient of 0.94. Similar comparison with the solar magnetic field (Bs) shows that EIpe correlates better with Bs than with F_10.7 . We also compare EIpe with total solar irradiance measured during the same period.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43713/1/11207_2004_Article_140430.pd

An unusual SAR arc observed during ring current development, 4 August 1972

Measurements made from the ISIS-II spacecraft at 1400 km and ground-based measurements from New Zealand provide a detailed description of an unusual SAR arc observed at dusk on 4 August 1972, during the growth phase of the ring current. Proton precipitation was observed over a latitude range of a few degrees, with electron temperature enhancements throughout the region but espeically at its boundaries, and an F-region trough was present at the equatorward boundary. SAR arcs usually occur at equatorward proton boundaries but this one appeared at the poleward boundary, which seems to have given rise to a number of unusual features. Characteristics unique to this event are a high flux of low energy electrons at the SAR arc location, associated with an upward field-aligned current there, and a "slot" in the ambient electron density, which falls to 5% of the background density over a region of 1.5 km half-width. Immediately poleward of the low energy electron flux, intense whistler mode noise (0.1-0.4 MHz) is evident. The 6300 A emission, which has a total intensity of 10.6 kR, appears divided into two components, one at 285 km excited by the low energy electrons, and the other at 400 km, excited thermally by the electron gas. Comparisons are made with S3-A spacecraft observations made in the equatorial region at the same time, with ISIS-II observations of a more normal SAR arc, and with other observations reported in the literature. The kinetic Alfven wave process described by Hasegawa and Mima (1978) seems a candidate for the acceleration of these low energy electrons, but it is not possible to entirely exclude the alternative of an auroral-type acceleration process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23358/1/0000302.pd

Satellite observations of new particle and field signatures associated with SAR arc field lines at magnetospheric heights

Enhancements in thermal ion densities, an oxygen dominated ring current at energies below 17 kev, and invariant latitude-limited bands of intense ELF hiss have been discovered on Stable Auroral Red (SAR) arc field lines at magnetospheric heights. These new signatures were revealed by an examination of 31 coordinated data sets taken simultaneously at magnetospheric and ionospheric heights by the DE-1 and -2 satellites during SAR arc traversals within the period September 1981 through April 1982. Data sets from DE-2, for the first time, provide information on the location of a SAR arc (determined by the F region electron temperature enhancement) during the nearly simultaneous passage of these field lines by DE-1 in the magnetosphere. These new high altitude signatures are examined in the context of possible magnetospheric SAR arc energy source mechanisms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26844/1/0000404.pd