Cross sections for electron impact ionization of molecules and rare gases are necessary for the modeling of phenomena related to the earth's upper atmosphere and to plasmas. The construction of an apparatus to improve the accuracy of measurements of such cross sections is reported. The ions are produced in a static gas target crossed by an electron beam and are counted with a new ion detector technology, which insures a increased accuracy of the ion flux measurement and of the target length. The target gas density is measured using an ionization gauge calibrated against a high accuracy capacitive transducer. This apparatus also features a pulsed mode of operation, which allows a product analysis through time of flight measurement.

A modified steady state flow/field model is applied to the direct interaction of the solar wind with the Martian ionosphere. The original flow/field model (Cloutier et al., 1987) is a one-dimensional, self-consistent derivation of differentials in vertical velocity, magnetic field, and ion densities from the coupled MHD equations. While successful in reproducing features of the ionosphere of Venus (Cloutier et al., 1987; McGary, 1987) and of Mars (Stewart, 1989), the flow/field model required an independently specified heating term (Q). The requirement of this term implies the presence of an energy source not accounted for in conventional calculations. This source was previously simulated with the inclusion of Q, but an unrecognized momentum or pressure term may also provide the coupling with the solar wind without the need of the free parameter Q. An in-depth analysis of Pioneer Venus data in relation to the total conservation of momentum of the system led to the discovery that the total momentum was in most cases not entirely accounted for, and that this "missing" term was correlated with solar wind dynamic pressure. By including this missing pressure, a new set of differential equations, which were also extended to include horizontal velocity terms, was derived. Extrapolation of the missing pressure to Mars gave results that faithfully reproduced the ionospheric features associated with previous flow/field models while maintaining agreement with Viking 1 and 2 observations. Finally, we suggest that the source of P$\sb{\rm missing}$ could be a population of suprathermal particles within the ionosphere. The missing pressures in the Viking simulations are consistent with measured suprathermal pressures at Mars (Hanson and Mantas, 1988).

The Pioneer Venus Orbiter Electric Field Detector (PVO OEFD) detected numerous impulsive electric field events in its 100 Hz channel when in nightside ionospheric troughs. What the source of the signals is has been under debate for over 10 years. Some researchers claim that lightning is generating whistler waves which are then being detected, while other researchers have supported the view that the signals are caused by a local generation of a plasma instability due to the conditions inside the troughs. We believe that the evidence collected by the PVO clearly disproves a lightning source and, in fact, points to an electrostatic wave as being the producer of the transients. We studied several wave modes in an effort to determine the source of the signals. We looked at the two-stream instability, the ion-acoustic instability, the gentle-bump instability, the lower-hybrid-drift instability and the Alfven wave mode. We found that not one of the wave modes studied could account for all of the signals. It would appear that there is not a large enough current within the troughs to support the two-stream instability. While the ion-acoustic instability may well be present within some troughs, the conditions needed to produce 100 Hz waves may not be universal trough conditions. Thus, this wave mode is not a likely generator of all the signals. The gentle-bump instability cannot produce 100 Hz waves and any Alfven waves will be damped. The lower-hybrid-drift instability seems to be the most likely candidate of the wave modes studied for producing the transient signals. The frequencies of the lower-hybrid-waves, however, appear to be too low to be detected by the OEFD. We believe that either the frequencies that we calculated are too small due to factors not taken into account, or there is a cascade of energy from the lower-hybrid waves to waves with frequencies that can be detected by the OEFD, or there is a combination of the two.

A series of improvements to the Rice Field Model (RFM) are described, which both increase the accuracy and extend the capabilities of the model. A new ring current parameterization improves the determination of storm-time fields in the inner magnetosphere. Replacement of the tail current module with a more flexible representation also contributes to improved accuracy in the inner magnetosphere, and enables realistic variations in current strength and orientation over the entire magnetotail length. Revision of the tail shielding/interconnection field eliminates inconsistencies in the model magnetotail, and permits variation in the normal component distribution over the tail portion of the magnetopause. The enhanced flexibilities of the interconnection field and cross-tail current module make possible the modeling of variations in the interplanetary magnetic field (IMF) as it propagates downstream, thereby advancing the steady-state RFM an important step toward time-dependent modeling. The modified RFM is used to explore a number of time-dependent magnetospheric phenomena. In simulations of the March 1998 magnetic storm, the new model displays an improved representation of the inner magnetosphere, accurately predicting both storm-induced variations and day-night asymmetry in the field at geosynchronous orbit. The effects of time-dependent interplanetary fields on magnetospheric convection are examined, using a new method to compute ionospheric flow and electric fields in non-steady configurations. This method is applied to simulations of the growth and contraction of the polar cap in Southward and Northward turnings of the IMF. Model convection patterns for Southward turnings are shown to be consistent with theoretical expectations. The RFM is also used to simulate polar cap convection in the particular IMF conditions believed to trigger formation of the theta aurora. The results of the simulation prove to be consistent with several observed properties of the theta aurora, and shed light on the plasma sheet and magnetotail configurations associated with this phenomenon.

Before the IMAGE mission, electron densities in the high latitude, high altitude region of the magnetosphere were measured exclusively by in situ means. The Radio Plasma Imager instrument onboard IMAGE is capable of remotely observing electron densities between 0.01 and 100,000 e-/cm-3 from distances of several Earth radii or more. This allows a global view of the high latitude region that has a far greater accuracy than was previously possible. Soundings of the terrestrial magnetic cusp provide the first remote observations of the dynamics and poleward density profile of this feature continuously over a 60-minute interval. During steady quiet-time solar wind and interplanetary magnetic field conditions, the cusp is shown to be stable in both position and density structure with only slight variations in both. Peak electron densities within the cusp during this time are found to be somewhat higher than predicted. New procedures for deriving electron densities from radio sounding measurements are developed. The addition of curve fitting algorithms significantly increases the amount of useable data. Incorporating forward modeling techniques greatly reduces the computational time over traditional inversion methods. These methods are described in detail. A large number high latitude observations of ducted right-hand extraordinary mode waves made over the course of one year of the IMAGE mission are used to create a three dimensional model of the electron density profile of the terrestrial polar cap region. The dependence of electron density in the polar cap on average geocentric distance (d) is found to vary as d-6.6. This is a significantly steeper gradient than cited in earlier works such as Persoon et al., although the introduction of an asymptotic term provides for basic agreement in the limited region of their joint validity. Latitudinal and longitudinal variations are found to be insignificant. Both the mean profile power law index of the electron density profile and, to a stronger degree, its variance show dependence with the DST index.

Methodologies using tunable laser absorption spectroscopy (TLAS) for quantifying carbon dioxide stable isotopes (13/12CO 2), measuring atmospheric formaldehyde (CH2O), and analyzing exhaled carbonyl sulfide (COS) in human breath are covered. Fundamental spectroscopic aspects that limit achievable precisions of 13/12CO2 isotopic ratio TLAS measurements have been investigated and include affects of temperature and pressure instabilities, differences in relative humidity between reference standards and sample gases, and the effect of gas heating from optical absorption. Experimental studies were designed and carried out to determine the best possible system configuration and analytical routines for ratiometric measurements. Direct absorption was found to be advantageous over 2nd harmonic detection in regards to precision measurements. Airborne spectral measurements of CH2O using a TLAS based instrument equipped with a lead-salt diode laser onboard a NASA DC-8 aircraft taken during the INTEX-NA 2004 mission was analyzed to assess instrument performance and reliability using standard and newly proposed statistical measures. An improvement in system performance after stabilization of optical components has been unambiguously shown. A retrospective analysis of stored spectral data has shown that methanol (CH3OH) concentrations can also be deduced along with CH2O concentrations using a least-squares singular-value decomposition regression routine. A TLAS instrument equipped with a thermo-electrically cooled pulsed quantum cascade (QC) laser was used to perform absorption measurements of carbonyl sulfide (COS) with detection limits near ∼3-ppbv. This instrument was fully characterized prior to conducting a small clinical study to perform offline measurements of COS in the exhaled breath of lung transplant patients to determine the utility of such measurements in diagnosing acute rejection (AR) of lung allografts. COS at ∼8-ppb was observed in one patient suffering from bronchiolitis.

Venus' nightside ionosphere may be characterized by two general magnetic field geometries. Most of the ionosphere is characterized by largely horizontal fields carried over across the terminator from the dayside. However, regions of mostly vertical fields, associated with the nightside ionospheric 'holes' and connected to regions in the ionosheath where there are strong tailward fields, are also present. A magnetic potential model has been developed to describe the interface of the ionosphere, represented as an infinite slab bounded by two magnetically impermeable planes, with the tail lobes idealized as semi-infinite solenoids terminating at the ionopause. From this model, ionospheric boundary currents are generated to confine all field lines in either the flat ionosphere or the vertical tail lobe, and the field geometries are explored. Techniques for mapping this solution to a sphere and approximating it at long ranges from the transition region are discussed, and a preliminary global nightside model is offered.

The El Nino phenomenon has a major impact over wide regions of the Pacific and possibly all over the world. The purpose of this thesis was to study its effects, specifically along the coast of British Columbia. An analysis of sea-surface temperature, sea-surface salinity and sea-level height was made with respect to El Nino events. Based on the results of that analysis, a model was developed. The model uses Kelvin wave dynamics, and can be used to predict the approximate time and magnitude of the sea-surface temperature anomaly created by an El Nino event. This prediction can be useful for fishermen because the anomaly of temperature has a major effect on the distribution pattern of fish. In conclusion, an analysis of water temperature and salinity anomalies as a function of depth as well as offshore distance was made.

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No description available.