Robert E. Boughner

Precipitating relativistic electrons - Their long-term effect on stratospheric odd nitrogen levels

Using electron count rate data at geostationary orbit, daily energy spectra, extending from 30 keV to 15 MeV, have been developed for trapped relativistic electrons at 6.6 RE These spectra have been used to model the flux of these electrons into the atmosphere at 120 km. Energy deposition calculations permit daily sources of HOx and NOy to be calculated at auroral and subauroral latitudes due to relativistic electron precipitation (REP) for the period June 13, 1979, through June 4, 1988. Both short-term and long-term source variations are quite large over the period considered. The long-term variation of the NOy source is found to reach a maximum in late 1984 and early 1985, with significant declines thereafter. Daily Solar Backscattered Ultraviolet (SBUV) O3 data show a significant response to these precipitation events. Two-dimensional model calculations have been carried out for the period 1979 to 1990 with REP effects included through June 4, 1988. Results suggest that globally integrated NOy has increased by 35–40% from 1979 to early 1985 with declines thereafter. The largest long-term increases are found in the lower stratosphere at the high latitudes. Comparisons of Limb Infrared Monitor of the Stratosphere (LIMS), Solar Mesospheric Explorer (SME), Stratospheric Aerosol and Gas Experiment (SAGE), and SAGE II NO2 data are consistent with these calculations. The results suggest that a significant contribution to the anomalously large and unexplained global O3 declines between 1979 and 1985 has been made by the catalytic destruction of O3 by odd nitrogen in the lower stratosphere at mid to high latitudes. The results also provide evidence for a clear and strong linkage between solar variability, the state of the magnetosphere, and the chemical climatological state of the middle and lower atmosphere.

Precipitating electrons: Evidence for effects on mesospheric odd nitrogen

Observations of electron fluxes made by the PET and LICA instruments aboard SAMPEX have been used with NO measurements made by HALOE aboard UARS to provide evidence of mesospheric and lower thermospheric NO formation due to precipitating electrons. Results indicate significant NO increases from 70 to 120 km which are associated with the occurrence of enhanced electron populations in the outer trapping regions of the magnetosphere, 2.5 ≤ L ≤ 7, which precipitate into the atmosphere.

On the origin of midlatitude ozone changes: Data analysis and simulations for 1979–1993

Satellite data show large declines in global (4.5%) and midlatitude (10%) ozone in the mid-1980s and during 1992 and 1993. Analyses of ozone, temperature, and aerosol records and two-dimensional chemical transport simulations have been carried out to develop an understanding of the causes of these changes. Simulations include contemporary homogeneous and heterogeneous chemistry. Also included are the effects of trace gas increases, dilution and denitrification associated with the Antarctic ozone destruction, solar cycle effects including relativistic electron precipitation (REP), variable diabatic transport fields and temperature, and variable sulfate aerosol surface area density and acidity. Simulated global and midlatitude ozone agree very well with observations for the entire period. Mid-1980s near-global ozone declines calculated by the model were found to be due to solar cycle (including REP) effects, -1.9%; volcanic effects, -1.5%; dilution effects, -1.1%; transport and temperature effects, -1%; and trace gas effects, -0.2%. The maximum effects of these different processes occur at different times. The observed 10% reductions in midlatitude ozone are reproduced in the simulations and are primarily due to 1 to 2-year transport and temperature variations.

The effect of paleoatmospheric ozone on surface temperature

Photochemical and radiative-convective calculations are performed to evaluate the influence of ozone in determining the surface temperature of the paleoatmosphere prior to the buildup of molecular oxygen to its present atmospheric level. Possible effects of atmospheric dynamics on the photochemistry and thermal structure of the paleoatmosphere are neglected, and the present atmospheric values are assumed for the tropospheric water-vapor relative-humidity distribution and lapse rate as well as for the fractional cloud amount and cloud reflectivity. It is found that the radiative effects (at IR and solar wavelengths) of ozone for a molecular oxygen level of one-tenth the present atmospheric level resulted in a globally averaged surface-temperature increase of about 4.5 K for the present solar constant. Implications of the results for paleoclimate are briefly considered.

Sensitivity of calculated odd nitrogen distributions to the diabatic wind fields

Two-dimensional and three-dimensional model calculations are known to give stratospheric total odd nitrogen (NOy = N + NO + NO2 + 2 × N2O5 + HNO3 + HNO4 + ClONO2) mixing ratios which are significantly smaller than values inferred using measurements obtained from the limb infrared monitor of the stratosphere (LIMS) instrument. We examine NOy distributions calculated with two different advective transport fields, one derived from reported climatological data and one derived from LIMS T, O3, and H2O data. Specifically, it is of interest to see if the use of the advective fields derived from the LIMS data leads to a reconciliation of the inferred and calculated NOy distributions. Calculations with the advective field derived from climatological data show stronger poleward and downward motion in the winter season compared to the advective field derived from LIMS data. This leads to NOy mixing ratios in the lower stratosphere that are about 20% larger in the polar regions of both hemispheres and approximately 40% higher in the equatorial region for climatological transport fields compared to those derived from LIMS data. As a consequence, the NOy distributions calculated in the present model with the LIMS advective field show worse agreement with NOy values inferred from the LIMS measurements than similar results obtained with the climatological wind field. Ozone levels in the lower stratosphere calculated with the climatological wind field are smaller than those computed with the LIMS wind field, which is most likely an indirect chemical effect associated with the larger NOy values.

Comets and the Photochemistry of the Paleoatmosphere

Ozone (O3) is a key atmospheric gas in considerations of the photochemistry/chemistry of the paleoatmosphere, chemical evolution, and the origin and evolution of life. The photochemistry/chemistry of atmospheric O3 in the paleoatmosphere is investigated using a one-dimensional photochemical model that includes the chemistry of the oxygen, nitrogen, hydrogen, carbon, and chlorine gases. The role of cometary influx of H2O on the photochemistry of the paleoatmosphere is also examined. Recently, it has been suggested that our planet received a significant portion of the volatiles presently in the atmospheric/oceanic/biospheric system from cometary volatile influx. Several consequences of a cometary H2O influx on the photochemistry and structure of the paleoatmosphere are presented.

A Study of the Ozone Photochemistry in the Upper Stratosphere Using LIMS Data

LIMS data at vernal equinox conditions are used to study the photochemistry of the upper stratosphere. The results indicate, and it has been recently reported, that with the use of recommended reaction rates, current models underestimate ozone mixing ratio by 20–40%. We also find that for ozone, good agreement with data is realized with the modification of six key reaction rates within the published limits of uncertainty. These modifications also yield better agreement with data for daytime NO2. Model results for other parameters such as the ratio HN03/N02, OH mixing ratio, and the temperature sensitivity of 03 are compared with data.

An improved separability approximation for line radiative transport in nonhomogeneous media.

Abstract A simple modification to the constant half-width approximation of Wilson and Greif, which is an extension of the well-known Curtis-Godson method to the treatment of temperature variations along the integration path, is introduced which permits a more accurate evaluation of line radiative transport in non- homogeneous gases. To demonstrate the methods accuracy, comparisons are made with Wilson and Greif and numerical frequency integrated results for the line equivalent width and radiative flux in a planar slab with prescribed Planck function and line half-width spatial variations are chosen to represent typical shock layer conditions. It is found that the modified procedure reduces the inaccuracies inherent in Wilson and Greifs approximation by factors ranging from 5 to 10, while retaining the latter methods ease of application.