ALBERT

Description: The Swedish microsatellite ASTRID was launched by a Russian Cosmos rocket on January 24, 1995 into a 1000 km circular orbit with 83 deg inclination. Besides the main objective of technological demonstration, imaging of energetic neutral atoms (ENAS) was attempted. The imager detected ENA in the energy range 0.1 - 140 keV utilizing two different techniques. Neutrals of the energy 13 - 140 keV were recorded by 14 solid state detectors with the total field of view 5 deg x 322 deg. For half a spin (approx. 1.5 s) of the ASTRID spacecraft, almost all of space was covered with an angular resolution 2.5 deg x 25 deg. Less energetic neutrals of approx. 0.1 - 70 keV were converted on a graphite target into secondary particles which then were detected by a microchannel plate with 32 anodes. A fraction of primary neutrals was directly reflected towards the sensor. This technique provided the total ENA flux with an angular resolution 4.6 deg x 11.5 deg. The instrument weight is 3.13 kg. Successful operation of the instrument during the first 5 weeks of the mission provided the first ENA images of the ring current at low altitudes.

Description: Two aspects of the cloud ice parameterization in the Goddard Cumulus Ensemble Model cloud physics parameterization are examined: the conversion of cloud ice to snow by depositional growth, designated PSFI, and the saturation adjustment scheme. The original formulation of PSFI is shown to produce excessive conversion of cloud ice to snow because of an implicit assumption that the relative humidity is 100% with respect to water even though the air may actually be quite less humid. Two possible corrections to this problem are proposed, the first involving application of a relative humidity dependent correction factor to the original formulation of PSFI, and the second involving a new formulation of PSFI based on the equation for depositional growth of cloud ice. The sensitivity of these formulations of PSFI to the assumed masses of the ice particles is examined. Possible problems associated with using a saturation adjustment scheme for cloud ice are discussed and simulations of a squall line with and without application of the adjustment scheme for ice are compared.

Description: Observations of energetic neutral atoms (ENA) in the energy range 26- 52 keV are reported from four occasions during geomagnetically disturbed periods. The data were acquired by the ENA imager flown on the Swedish microsatellite Astrid in a 1000 km circular orbit with 83 deg inclination. The ENA imager separates charged particles from neutrals through an electrostatic deflection system in the energy range between 0.1 and 114 keV. ENA images obtained from vantage points in the polar cap and in the afternoon magnetic local time (MLT) hours looking into the antisunward hemisphere show intense ENA fluxes (approx. 10(exp 4)/sq cm sr s over 26-37 keV) coming from the dusk region and low altitudes (approx. 300 km). The morphology shows no relation to local magnetic field excluding the possibility of charged particle detection. It is concluded that the source of these ENAs are precipitating/mirroring ions from the ring current/trapped radiation interacting with the exobase on auroral L-shells and in the dusk region. The observed ENA fluxes show a relation with Kp and Dst geomagnetic indices. The observed ENA spectrum from a geomagnetic storm on February 8, 1995, is investigated in more detail and compared to the parent ion spectrum obtained by the Defense Meteorological Satellite Project (DMSP) satellite, Fl2, during the same period on L = 6 +/- 2 around dusk. The observed ENA spectral slope is used to derive the parent ion spectral temperature. The derived ion temperatures range is 3.0 - 6.0 keV for H and 4.5 - 8.5 keV for O. The higher of these ion temperatures comes closest in agreement to the extrapolated DMSP spectrum leading us to favor O over H as the species of the detected ENAS. It is shown that the detected ENAs must have been produced at L greater than or equal to 6 to reach the detector without atmospheric attenuation and that the main energy dependence of the ENA spectrum, apart from the parent ion spectrum, is governed by the energy dependence of the charge exchange cross section between ions and exospheric oxygen.

Description: The purpose of this project was to determine the suitability of measuring active deformation of volcanoes in Alaska using Interferometric Synthetic Aperture Radar (INSAR) techniques. Work sponsored by this grant supported one graduate student (for almost 2 years) and one postdoc (for several months), and has resulted in two published peer-reviewed papers and a front-page article in EOS. An additional paper is in review and a fourth is in preparation. An additional paper in preparation was based in part on research supported by this grant and in part by a successor grant from NASA's Solid Earth Natural Hazards program. Over the course of this research, we documented measurable uplift of Trident volcano in the Katmai group, conducted a systematic study of the change in phase coherence over time on volcanic surfaces, and measured and modeled the spectacular 1.5 m deflation of Okmok caldera associated with its 1997 eruption. We also generated initial interferograms spanning the 1996 seismic swarm of Akutan volcano; however, during the period covered by this project we were not able to remove topography. That has been done under the subsequent funding and a paper is now in preparation. This report summarizes work done under two separate contracts because both were based on the same proposal to NASA's ADRO (Application Development and Research Opportunity) program. The first year was funded out of a grant from NASA Headquarters and the second and third years out of a grant through Goddard. The work, however, was a continuous three year effort.

Description: This study investigates the evolution of the magnetotail's magnetic field with the aid of a self-consistent two-dimensional model in which the ion current periodically updates the magnetic field. The plasma mantle supplies particles continuously to the magnetotail, and the perturbation magnetic field is calculated from the ion current using the Biot-Savart law. The simulated magnetotail evolves into a quasi-steady state, characterized by the periodic motion of the near-Earth X-line in the model. This variability is caused by the nonadiabatic acceleration of ions in the current sheet and their rapid loss from the tail. Particularly noteworthy is the value found for the characteristic time scale of variability in the magnetotail. on the order of 4 - 5 minutes.

Description: This study investigates the evolution of the magnetotail's magnetic field with the aid of a self-consistent two-dimensional model. In this model the plasma mantle continuously supplies particles to the magnetotail, the ion current periodically updates the magnetic field using the Biot-Savart law. The simulated magnetotail evolves into a quasi-steady state, characterized by the periodic motion of the model's near-Earth X-line. This variability results from the nonadiabatic acceleration of ions in the current sheet and their rapid loss from the tail. The characteristic time scale of variability in the magnetotail is on the order of 4 - 5 minutes. We also investigate how the magnetotail's topology responds to increased convection electric fields, and show examples of observations of variability in the magnetotail.

Description: This study employs Geotail plasma observations and numerical modeling to determine sources of the ions observed in the near-Earth magnetotail near midnight during a substorm. The growth phase has the low-latitude boundary layer as its most important source of ions at Geotail, but during the expansion phase the plasma mantle is dominant. The mantle distribution shows evidence of two distinct entry mechanisms: entry through a high latitude reconnection region resulting in an accelerated component, and entry through open field lines traditionally identified with the mantle source. The two entry mechanisms are separated in time, with the high-latitude reconnection region disappearing prior to substorm onset.

Description: Observational studies were performed of westward propagating synoptic scale waves in the tropical troposphere, the structure of monsoon circulations in the upper troposphere and lower stratosphere, and zonally propagating features in deep tropical convection. The effect of the quasi-biennial oscillation (QBO) were investigated, and a numerical study of the QBO was performed using a two-dimensional model, highlighting the role of gravity waves in the momentum balance of the QBO. Vertical coupling of the troposphere and stratosphere was examined in polar regions on intraseasonal and interannual timescales. A deep circumpolar mode was discovered, now known as the Arctic Oscillation.

Description: Remote airborne measurements of the vertical and horizontal structure of the atmospheric pressure field in the lower troposphere are made with an oxygen differential absorption lidar (DIAL). A detailed analysis of this measurement technique is provided which includes corrections for imprecise knowledge of the detector background level, the oxygen absorption fine parameters, and variations in the laser output energy. In addition, we analyze other possible sources of systematic errors including spectral effects related to aerosol and molecular scattering interference by rotational Raman scattering and interference by isotopic oxygen fines.

Description: The first in situ measurements of ClONO2 in the lower stratosphere, acquired using the NASA ER-2 aircraft during the Polar Ozone Loss in the Arctic Region in Summer (POLARIS) mission, are combined with simultaneous measurements of ClO, NO2, temperature, pressure, and the calculated photolysis rate coefficient (J(sub ClONO2)) to examine the balance between production and loss of ClONO2. The observations demonstrate the ClONO2 photochemical steady state measurement, [ClONO2](sup PSS) = k[ClO][No2]/J(sub ClONO2), is in good agreement with the direct measurement, [ClONO2](sup MEAS). For the bulk of the data (80%), where T 〉 220 K and latitudes 〉 45 N, [ClONO2](sup PPS) = 1.15 +/- 0.36(1-sigma)[ClONO2](sup MEAS), while for T〈 220 K and latitudes 〈 45 N, the result is somewhat less at 1.01 +/- 0.30. The cause of the temperature and/or latitude trend is unidentified. These results are independent of solar zenith angle and air density, thus there is no evidence in support of a pressure-dependent quantum yield for photodissociation of ClONO2 at wavelengths 〉 300 nm. These measurements confirm the mechanism by which active nitrogen (NOx = NO + NO2) controls the abundance of active chlorine (Clx = ClO + Cl) in the stratosphere.