Showing papers by "James Walega published in 1994"

Distributions of NO, NOx, NOy, and O3 to 12 km altitude during the summer monsoon season over New Mexico

Abstract: During late July and August 1989, 12 flights of the National Center for Atmospheric Research Sabreliner jet aircraft were made over New Mexico when the region was dominated by either synoptic high pressure or moist “monsoon” flow. In the latter case, sampling was made within and about deep convective clouds which were sometimes electrically active. A summary of the measurements of the species listed in the title and their ratios are given. These distributions include signatures from deep convection, lightning production of odd nitrogen, aircraft exhaust emissions, and possible stratospheric input. The averages and range of these distributions are considered to be more representative of typical summer conditions over the region compared to flights that are often restricted more to fair weather situations. Coherence between the O3 and the NOy observations is compared to results from other ground-based and aircraft programs and possible contributing factors are discussed. Because the measurements were made with then newly developed instrumentation, its capabilities and shortcomings are summarized.

Meridional distributions of NOx, NOy, and other species in the lower stratosphere and upper troposphere during AASE II

Abstract: The meridional distribution of NO(x) in the lower stratosphere and upper troposphere is inferred form 10 flights of the NASA DC-8 in the northern winter of 1992 along with like distributions of NO(y), NO(x)/NO(y), CO, and C2Cl4. In the lowest few km of the stratosphere there is little vertical gradient in NO(x) over the range of latitiudes measured (40 deg-90 deg N). There is a substantial latitudinal gradient, with 50 pptv above the pole and 120 pptv near 40 deg N. In the uppermost few km of the troposphere, background values range from 30 pptv over the pole to 90 pptv near 40 deg N. On two occasions higher values, up to 140 pptv in the mean, were seen 2-3 km below the tropopause in association with frontal systems. The meridional distributions of CO and C2Cl4 show the same feature, suggesting that the source of the elevated NO(x) is near the earth's system.

Parameterization of subgrid scale convective cloud transport in a mesoscale regional chemistry model

Abstract: A parameterization of subgrid scale convective cloud vertical mixing has been developed in the National Oceanic and Atmospheric Administration Aeronomy Laboratory three-dimensional regional chemistry model. The parameterization is evaluated by comparing model results (with and without the cloud mixing parameterization) with observations of O{sub 3}, NO{sub x}, and NO{sub y} made onboard the National Center for Atmospheric Research Sabreliner aircraft during the 1990 Rural Oxidants in the Southern Environment campaign in Alabama. The authors` studies show that model results with and without the cloud transport significantly differ from each other when convective clouds are present, implying that cloud exchange is an important process in determining the distributions of trace species. Their studies also show that model results with cloud transport parameterization are in much better agreement with the aircraft observations than those without. 45 refs., 13 figs., 2 tabs.

Three‐dimensional model interpretation of NO x measurements from the lower stratosphere

Abstract: A three-dimensional off-line chemistry transport model, driven by European Center for Medium-Range Forecasts winds and temperatures, is used to interpret measurements of NO and NO2 taken from the DC-8 during the second Airborne Arctic Stratospheric Expedition. The model was run in three configurations: gas phase chemistry alone, inclusion of the N2O5 aerosol reaction, and inclusion of both N2O5 and ClONO2 aerosol reactions. The run including the N2O5 aerosol reaction alone usually agreed best with measured NO(x)/NO(y) ratios in midlatitude air masses. The NO(x)/NO(y) ratios of the run with both aerosol reactions were always too low, while the gas phase ratios were usually too high, especially during March. All three simulations generated extremely low NO2/NO(y) ratios in air parcels that had spent several days or more in the polar night. Measured NO2/NO(y) ratios in these types of air masses were sometimes equally low but could also be considerably higher. Observed NO/NO2 ratios differed strongly from known theory.