J. O. Ballenthin

The February–March 2000 Eruption of Hekla, Iceland from a Satellite Perspective

An 80,000 km 2 stratospheric volcanic cloud formed from the 26 February 2000 eruption of Hekla (63.98° N, 19.70° W). POAM-III profiles showed the cloud was 9-12 km asl. During 3 days this cloud drifted north. Three remote sensing algorithms (TOMS SO 2 , MODIS & TOVS 7.3 μm IR and MODIS 8.6 μm IR) estimated ∼0.2 Tg SO 2 . Sulfate aerosol in the cloud was 0.003-0.008 Tg, from MODIS IR data. MODIS and AVHRR show that cloud particles were ice. The ice mass peaked at ∼1 Tg ∼10 hours after eruption onset. A ∼0.1 Tg mass of ash was detected in the early plume. Repetitive TOVS data showed a decrease of SO 2 in the cloud from 0.2 Tg to below TOVS detection (i.e.<0.01 Tg) in ∼3.5 days. The stratospheric height of the cloud may result from a large release of magmatic water vapor early (1819 UT on 26 February) leading to the ice-rich volcanic cloud. The optical depth of the cloud peaked early on 27 February and faded with time, apparently as ice fell out. A research aircraft encounter with the top of the cloud at 0514 UT on 28 February, 35 hours after eruption onset, provided validation of algorithms. The aircrafts instruments measured ∼0.5-1 ppmv SO 2 and ∼35-70 ppb sulfate aerosol in the cloud, 10-30% lower than concentrations from retrievals a few hours later. Different SO 2 algorithms illuminate environmental variables which affect the quality of results. Overall this is the most robust data set ever analyzed from the first few days of stratospheric residence of a volcanic cloud.

Chemical ionization mass spectrometer technique for the measurement of HNO3 in air traffic corridors in the upper troposphere during the SONEX campaign

A chemical ionization mass spectrometer (CIMS) was used for rapid detection of HNO3 in air traffic corridors, primarily over the North Atlantic region, during the NASA Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) campaign in the fall of 1997. The sensitivity of the CIMS instrument approaches 1 ion count per second for each 106 molecules cm−3, under ideal conditions. During the SONEX mission the precision of the experiment was considerably lower due to inlet fluctuations. Ten-second integration periods were used to obtain a precision of typically 10 parts per trillion by volume. A description is given of the instrument and the technique, including inflight calibration using a permeation tube. Comparisons are made with NOy data and with the University of New Hampshire HNO3 data obtained with a mist chamber method.

Chemical ionization mass spectrometric measurements of SO2 emissions from jet engines in flight and test chamber operations

We report the results of two measurements of the concentrations and emission indices of gas-phase sulfur dioxide (EI(SO2)) in the exhaust of an F100–200E turbofan engine. The broad goals of both experiments were to obtain exhaust sulfur speciation and aerosol properties as a function of fuel sulfur content. In the first campaign, an instrumented NASA T-39 Sabreliner aircraft flew in close formation behind several F-16 fighter aircraft to obtain near-field plume composition and aerosol properties. In the second, an F-100 engine of the same type was installed in an altitude test chamber at NASA Glenn Research Center where gas composition and nonvolatile aerosol concentrations and size distributions were obtained at the exit plane of the engine. In both experiments, SO2 concentrations were measured with the Air Force Research Laboratory chemical ionization mass spectrometer as a function of altitude, engine power, and fuel sulfur content. A significant aspect of the program was the use of the same fuels, the same engine type, and many of the same diagnostics in both campaigns. Several different fuels were purchased specifically for these experiments, including high-sulfur Jet A (∼1150 ppmm S), low-sulfur Jet A (∼10 ppmm S), medium-sulfur mixtures of these two fuels, and military JP-8+100 (∼170 and ∼300 ppmm S). The agreement between the flight and test cell measurements of SO2 concentrations was excellent, showing an overall precision of better than ±10% and an estimated absolute accuracy of ±20%. The EI(SO2) varied from 2.49 g SO2/kg fuel for the high-sulfur fuel in the test chamber to less than 0.01 g/kg for the lowest-sulfur fuel. No dependence of emission index on engine power, altitude or simulated altitude, separation distance or plume age, or the presence of contrails was observed. In all experiments the measured EI(SO2) was consistent with essentially all of the fuel sulfur appearing as gas-phase SO2 in the exhaust. However, accurate determination of S(IV) to S(VI) conversion was hampered by inconsistencies in the assays of total fuel sulfur content.

In situ HNO3 to NOy instrument comparison during SOLVE

Measurements of HNO 3 mixing ratios from the chemical ionization mass spectrometer have been critically compared with simultaneous measurements of total gas phase NO y from the NO chemiluminescence detector aboard the NASA DC-8 aircraft during the SAGE 3 Ozone Loss and Validation Experiment (SOLVE). The data were obtained in the arctic upper troposphere and lower stratosphere in the winter of 1999-2000. A brief comparison to the NOy instrument aboard the NASA ER-2 is also presented. The time responses, detection limits, relative precision, and stability of relative calibrations for the instruments were in excellent agreement throughout the mission. However, the average slope of the HNO 3 to NO y correlation was 1.13 ± 0.03 overall and 1.06 ± 0.03 in stratospheric air, indicating that the two measurements had a systematic calibration offset. Possible sources for the offset error are presented, and methods to reduce the calibration error in future flights are suggested.

Assimilative modeling of observed postmidnight equatorial plasma depletions in June 2008

Abstract : The Communications/Navigation Outage Forecasting System (C/NOFS) satellite observed large-scale density depletions at postmidnight and early morning local times in the Northern Hemisphere summer during solar minimum conditions. Using electric field data obtained from the vector electric field instrument (VEFI) as input, the assimilative physics-based model (PBMOD) qualitatively reproduced more than 70% of the large-scale density depletions observed by the Planar Langmuir Probe (PLP) onboard C/NOFS. In contrast, the use of a climatological specification of plasma drifts in the model produces no plasma depletions at night. Results from a one-month statistical study found that the large-scale depletion structures most often occur near longitudes of 60 deg, 140 deg, and 330 deg, suggesting that these depletions may be associated with nonmigrating atmospheric tides, although the generation mechanisms of eastward electric fields at postmidnight local times are still uncertain. In this paper, densities obtained from both assimilation and climatology for the entire month of June 2008 are compared with PLP data from C/NOFS and the Challenging Minisatellite Payload (CHAMP), as well as special sensor ionospheric plasma drift/scintillation meter (SSIES) measurements from the Defense Meteorological Satellite Program (DMSP) satellites. Our statistical study has shown that, on average, the densities obtained by the PBMOD, when it assimilates VEFI electric fields, agree better with observed background densities than when PBMOD uses climatological electric fields.

The Compact Environmental Anomaly Sensor Risk Reduction: A Pathfinder for Operational Energetic Charged Particle Sensors

Compact environmental anomaly sensor risk reduction (CEASE-RR) is a new sensor designed for anomaly attribution due to the space radiation environment. It does this using two solid-state particle telescopes that have been designed to measure proton and electron fluxes that are the drivers for three of the four primary space environment effects (event total dose, deep-dielectric charging, and single event effects). These telescopes are integrated into a compact package along with space reserved for a planned electrostatic analyzer being developed for the final CEASE 3 design (covering the fourth primary space environment effect—surface charging). The sensors themselves will measure a wider dynamic range in particle flux, provide higher energy resolution, have better out-of-band contamination rejection, and improved diagnostic capability compared to previous CEASE instruments. The CEASE-RR instrument is planned to be launched in 2018 to geostationary orbit as part of an Air Force Research Laboratory flight experiment. The sensor design, calibration, and planned flight experiment objectives are described in this paper.

Correction to “Nitric acid condensation on ice: 1. Non-HNO3 constituent of NOY condensing on upper tropospheric cirrus particles”

[1] Measurements of NOy condensation on cirrus particles during the SOLVE-I field campaign are analyzed and segregated based on altitude. Significant amounts ofNOywere found on the upper tropospheric ice particles; therefore condensation on ice appears to be an important method of NOy removal from the gas phase at the low temperatures of the Scandinavian upper troposphere. For the data set collected on 23 January 2000, NOy condensation on cirrus particles has different properties depending on whether the ice particles are sampled in the upper troposphere, where HNO 3 does not dominate NO Y , or in the lower stratosphere, where HNO 3 does dominate NOy Nitric acid becomes enriched in the gas phase as NOy condenses on upper tropospheric ice crystals, indicating that a non-HNO 3 component of NOy is condensing on upper tropospheric ice particles much faster and at higher concentrations than HNO 3 alone on this day. It is unclear which non-HNO 3 constituent of NOy is condensing on upper tropospheric ice particles, although N 2 O 5 is the most likely species. This condensation of a non-HNO 3 component of NOy is not universal in the upper troposphere but depends on the conditions of the air parcel in which sampling occurred, notably exposure to sunlight.