Geophysical Research Letters

Shuchman, R. A.; Meadows, G. A.

doi: 10.1029/GL007i011p00857pmid: N/A

Ravishankara, A. R.; Kreutter, N. M.; Shah, R. C.; Wine, P. H.

doi: 10.1029/GL007i011p00861pmid: N/A

The laser/flash photolysis‐resonance fluorescence technique was employed to study the kinetics of the reaction OH + COS →k1 products. Complicating secondary reactions involving COS photofragments were eliminated by using 193 nm laser photolysis of HNO3 as a source of OH. The rate constant was found to be much slower than previous measurements indicated. Based on our experiments, the upper limit for k1 at 298K is 8.8 × 10−15 cm³molecule−1s−1. Our results suggest that the title reaction is only a minor COS degradation pathway in the troposphere.

Brinton, H. C.; Taylor, H. A.; Niemann, H. B.; Mayr, H. G.; Nagy, A. F.; Cravens, T. E.; Strobel, D. F.

doi: 10.1029/GL007i011p00865pmid: N/A

The concentration of atomic hydrogen in the Venus thermosphere near 165km altitude and ∼18° north latitude has been derived from Pioneer Venus in situ measurements of n(H+), n(O+), n(O), and n(CO2), under the assumption of chemical equilibrium. Altitude profiles of derived n(H) suggest that chemical equilibrium prevails to an altitude of at least 200km on the dayside and to 165 km on the nightside. Measurements below these limits were made by the ion and neutral mass spectrometers on the orbiter spacecraft between December 1978 and July 1979, while periapsis traversed a complete diurnal cycle. The hydrogen concentration is found to rise sharply at both terminators from a dayside value of ∼5 × 104 cm−3, and to exhibit an asymmetric nightside distribution with a peak density in the predawn sector approximately 400 times greater than the dayside value. Analysis suggests that wind‐induced diffusion, combined with exospheric return flow, can account for the observed hydrogen behavior. The large day‐night temperature contrast enhances advective transport, which produces the large n(H) diurnal variation; the shift of the n(H) nighttime maximum toward dawn is caused by atmospheric superrotation.

Marché, Pierre; Barbe, Alain; Secroun, Claude; Corr, John; Jouve, Pierre

doi: 10.1029/GL007i011p00869pmid: N/A

The vertical profile and total column concentration of HCl have been measured from ground based high resolution infrared absorption spectra. The lines recorded were the R1 and P5 of HCl35 at 2942.731 cm−1 and 2775.760 cm−1 respectively. Vertical profiles and column concentrations are reported for different seasons. Measurements indicate an HCl volume mixing ratio equal to (2.2 ± 0.5) × 10−11 at 10 km increasing to (3.4 ± 0.6) × 10−9 at 33 km.

Mauersberger, K.; Finstad, R.

doi: 10.1029/GL007i011p00873pmid: N/A

A mass spectrometer experiment for the analysis of minor constituents in the stratosphere has been flown successfully four times from Palestine, TX on board a balloon gondola. The carbon dioxide mixing ratio, which shows unexpectedly large variations in the stratosphere, reached 400 ppm in one particular night flight. This is about 20% higher than the ground value. Evidence is presented that the experiment performed well during each of the balloon flights. The isotopic ratio 12C/13C was measured and found in good agreement with previous air analyses showing a depletion of 13C.

Lui, A. T. Y.; Akasofu, S. ‐I.

doi: 10.1029/GL007i011p00877pmid: N/A

It is shown that the north‐south component of electric fields in the plasma sheet can be estimated uniquely from simultaneous measurements of plasma flow components (vx, vy) and the magnetic field components (Bx, By) in the equatorial plane. The estimated field strength ranges from 0.3 to 7.8 mV/m during substorms at geocentric distances beyond ∼ 15 Re. During the magnetospheric substorm expansion phase, the north‐south component of the electric fields is almost oppositely directed from what one would expect on the basis of projection of the general pattern of the ionospheric electric field to the plasma sheet along geomagnetic field lines (assumed to be equipotential). It is only during the recovery phase when both electric field patterns become similar. The result also suggests that strong fields occur preferentially near the plasma sheet boundary rather than near the neutral sheet region.

Maynard, N. C.; Aggson, T. L.; Heppner, J. P.

doi: 10.1029/GL007i011p00881pmid: N/A

An example of large sub‐auroral poleward electric fields, similar to those observed on OGO‐6, S3‐2 and AE‐C (recently referred to as SAID) has been found in the magnetosphere near L = 4 and 2300 MLT using ISEE‐1 electric field data. The event is located adjacent to and outside the plasmapause and occurs 1½ hours into a substorm. The event is accompanied by a significant penetration of the convection electric field inside the plasmasphere. Data from similar regions on the next orbit occurring near the beginning of a substorm did not exhibit these effects. Recent theoretical models predict SAID to occur in the trough regions, where substorm dynamics force currents to flow in regions of low conductivity. These models provide a first‐order interpretation of this phenomena; however, the overall picture is more complex.

Meyers, Philip A.; Owen, Robert M.

doi: 10.1029/GL007i011p00885pmid: N/A

Fatty acid and organic carbon contents have been measured in the particulate and dissolved phases of surface microlayer and subsurface water samples collected from Lake Michigan. Concentrations are highest close to fluvial sources and lowest in offshore areas, yet surface/subsurface fractionation is lowest near river mouths and highest in open lake locations. These gradients plus accompanying fatty acid compositional changes indicate that river‐borne organic materials are important constituents of coastal Lake Michigan microlayers and that sinking and turbulent resuspension of particulates affect surface film characteristics. Lake neuston and plankton contribute organic components which partially replace potamic materials removed by sinking.

Ashour‐Abdalla, M.; Leboeuf, J. N.; Dawson, J. M.; Kennel, C. F.

doi: 10.1029/GL007i011p00889pmid: N/A

We present results of a computer simulation study of electron cyclotron harmonic waves. We model the initial electrons velocity distribution function as a hot ring perpendicular to the ambient magnetic field and a cold Maxwellian component. We identify nonlinear cyclotron resonance as the saturation mechanism of the unstable waves and as the heating mechanism of the cold electrons.

Murrow, P. J.; Rose, W. I.; Self, S.

doi: 10.1029/GL007i011p00893pmid: N/A

Grain size analysis of samples representing all sampleable portions of the airfall deposit produced by the Fuego volcano in Guatemala on 14 October 1974 form the basis for estimating the total grain size distribution of tephra from this eruption. The region enclosed by each isopach has a particular average grain size distribution which can be weighted proportionally to its percentage volume. The grain size of pyroclastic avalanche deposits produced during the eruption are also included. The total grain size distribution calculated as a sum of weighted distributions has a median grain size of 0.8∅ (0.6mm) and a sorting coefficient (σ∅) of 2.3. The size distribution seems to approximate Rosin and Rammler's law of crushing and this observation allows us to estimate that no more than 15% volume of the fine tail of the total size distribution is likely to be missing. The ash composed of these fine particles did not fall in the region of the volcano as part of the recognizable tephra blanket. The eruption column reached well into the stratosphere: heights estimated from the ground were 10‐12 km above sea level but estimated heights based on mass flux rates are higher (18‐23 km). The proportion of ash smaller than 2 µm, which could remain for substantial periods in the stratosphere, is no more than 0.8% volume of the total. It seems probable that acid aerosol particles from vulcanian type eruptions are more important to stratospheric aerosol perturbation than fine silicate ash particles by at least an order of magnitude.