Maryland Shared Open Access Repository
MD-SOAR is a shared digital repository platform for twelve colleges and universities in Maryland. It is currently funded by the University System of Maryland and Affiliated Institutions (USMAI) Library Consortium (usmai.org) and other participating partner institutions. MD-SOAR is jointly governed by all participating libraries, who have agreed to share policies and practices that are necessary and appropriate for the shared platform. Within this broad framework, each library provides customized repository services and collections that meet local institutional needs. Please follow the links below to learn more about each library's repository services and collections.
Browse
Communities and Collections | By Issue Date | Author | Titles | Subjects | TypeSubmit
Institutions in MD-SOAR
Select a community to browse its collections.
Recent Submissions
TRACE A trajectory intercomparison: 2. Isentropic and kinematic methods
(AGU, 1996-10-01) Fuelberg, Henry E.; Loring Jr., Robert O.; Watson, Mark V.; Sinha, M. C.; Pickering, Kenneth E.; Thompson, Anne M.; Sachse, Glen W.; Blake, Donald R.; Schoeberl, Mark R.
Kinematic and isentropic trajectories are compared quantitatively during a single 5-day period (October 13–18, 1992) when several flights for the Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE A) experiment were conducted off the west coast of Africa. European Centre for Medium-Range Weather Forecasts (ECMWF) data are used to compute the 5-day backward trajectories arriving at locations over the South Atlantic Ocean and nearby parts of South America and southern Africa. Two versions of kinematic trajectories are examined. One version employs vertical motions supplied with the ECMWF data. These trajectories often differ greatly from those based on the isentropic assumption. The kinematic trajectories usually undergo considerably greater vertical displacements than their isentropic counterparts; however, most diabatic rates are consistent with those of synoptic-scale systems. Ratios of acetylene to carbon monoxide are related to backward trajectories at various locations along a TRACE A flight. A second version of kinematic trajectories employs vertical motions diagnosed from ECMWF horizontal wind components using the continuity equation. These vertical motions are stronger than those supplied with the ECMWF data, causing many of the trajectories to have larger vertical displacements and considerably different paths than the original kinematic versions. Many of these kinematic trajectories undergo diabatic rates that exceed generally accepted values on the synoptic scale. This occurs, in part, because the diagnosed vertical motions are inconsistent with the ECMWF data. The research indicates that the kinematic procedure yields realistic 5-day backward trajectories when the three-dimensional wind data are available from a numerical model or other dynamically consistent data set such as provided by ECMWF.
Vertical ozone distribution over southern Africa and adjacent oceans during SAFARI-92
(AGU, 1996-10-01) Diab, R. D.; Thompson, Anne M.; Zunckel, M.; Coetzee, G. J. R.; Combrink, J.; Bodeker, G. E.; Fishman, J.; Sokolic, F.; McNamara, D. P.; Archer, C. B.; Nganga, D.
A set of four ozonesonde stations located at Ascension Island, Brazzaville, Okaukuejo, and Irene, operational during the TRACE A and SAFARI-92 experiments has provided an opportunity to investigate the vertical distribution of ozone over southern Africa and adjacent oceans. All stations display a springtime maximum in tropospheric ozone. Enhanced tropospheric ozone, which occurs between June and September at Brazzaville and between July and October at Ascension Island, is linked to dry season biomass burning. The influence of tropical biomass burning is delayed until September at Okaukuejo when a sharp increase in tropospheric ozone is experienced. The biomass burning influence at Irene is less because of its more southerly location. A general tropospheric enhancement is observed at all stations. It is manifest as an enriched layer in the upper troposphere at Okaukuejo (9–12 km) and Brazzaville (11–14 km) and in the lower troposphere (2–8 km) at Ascension Island. At Ascension Island lower tropospheric ozone values are about 20 parts per billion by volume greater than elsewhere and the tropospheric component here accounts for about 18% of the total column ozone. A series of tethersonde soundings conducted at hourly intervals at Okaukuejo revealed ozone to be well mixed in the lower boundary layer during the day, but to display marked vertical stratification at night.
Ozone over southern Africa during SAFARI-92/TRACE A
(AGU, 1996-10-01) Thompson, Anne M.; Diab, R. D.; Bodeker, G. E.; Zunckel, M.; Coetzee, G. J. R.; Archer, C. B.; McNamara, D. P.; Pickering, K. E.; Combrink, J.; Fishman, J.; Nganga, D.
Characteristics of total O3 in southern Africa and over the adjacent Atlantic during the IGAC/STARE/SAFARI-92/TRACE A (International Global Atmospheric Chemistry/South Tropical Atlantic Regional Experiment/Southern African Fire Atmospheric Research Initiative/Transport and Atmospheric Chemistry near the Equator-Atlantic) field experiments are described. Most of the analysis is based on data from the Nimbus 7/total ozone mapping spectrometer (TOMS) gridded O3 data archive (version 6.0), which is used to examine O3 in terms of seasonal and interannual variability. Total O3 column variability is compared to the tropospheric O3 column derived from balloonborne ozonesondes at four fixed SAFARI-92/TRACE A sites (Ascension Island, Brazzaville, Okaukuejo, and Irene) from September 1 to October 23, 1992. All of these sites except Okaukuejo had regular ozonesonde launches from 1990 to 1992. Total O3 and integrated tropospheric O3 at the sounding sites showed the expected September–October maxima over southern Africa and the adjacent Atlantic Ocean. Statistical analysis of the TOMS record for 1979–1992 allows disaggregation of components contributing to total O3 variability: Signals due to semiannual and annual cycles and the quasi-biennial oscillation are identified at the sounding sites. The tropospheric O3 column estimated from integrated sondes (to ?16 km) at the four sites ranged from 24 to 62 Dobson units (DU) (mean, 45 DU) and averaged 15% of total O3 at Irene (14 launches) and 19% of total O3 at Ascension (20 launches). Tropospheric O3 was higher at Ascension and Brazzaville than at the sites south of 15°S because transport from biomass burning regions was more direct at these sites. This transport is seen in Hovmöller (time-longitude) plots of total O3. A comparison of 1990–1992 integrated tropospheric O3 amounts with the annual total ozone cycle shows that tropospheric ozone variations may account for all of the annual signal at Ascension (8°S) and Brazzaville (4°S) but only 30–40% of the seasonal total O3 variation at Irene (26°S). Hovmöller plots of daily TOMS O3 over southern Africa and the Atlantic show easterly flow of local O3 maxima at 0°–10°S and westerly movement from 30°–40°S. At 0°–10°S the continent-ocean total O3 gradient and Ascension and Brazzaville O3 soundings are used to estimate a photochemical O3 formation rate of 1–2 ppbv O3/d over the Atlantic. This agrees with model calculations of moderately aged biomass burning emissions from SAFARI-92/TRACE A [Jacob et al., this issue; Thompson et al., 1996, this issue].
TRACE A trajectory intercomparison. 1. Effects of different input analyses
(AGU, 1996-10-01) Pickering, Kenneth; Thompson, Anne M.; McNamara, Donna; Schoeberl, Mark; Fuelberg, Henry; Loring, Robert; Watson, Mark; Fakhruzzaman, Khan; Bachmeier, A.
We address the problem of air mass trajectory uncertainty through an intercomparison of trajectories computed from operational meteorological analyses from the region and time period of the NASA/GTE/TRACE A experiment. This paper examines the trajectory uncertainty that results from the input meteorological analyses. We first compare the National Meteorological Center (NMC) and European Centre for Medium-Range Forecasts (ECMWF) meteorological analyses to an independent set of observations, the dropsondes released from the NASA DC-8 over the South Atlantic during TRACE A. We also compare the gridded wind and temperature fields with selected rawinsonde data that entered the analyses. These comparisons show that the ECMWF fields are marginally better than the ones from NMC, particularly in the tropical regions of the southern hemisphere. The NMC analyses are marginally better in the midlatitude westerlies in some cases. In general, slightly more confidence can be placed in trajectories computed with ECMWF data over the TRACE A region, based on our comparisons of the analyses with observations. Second, we compute 5-day back trajectories with three different models from a grid of points over the South Atlantic and adjacent portions of South America and Africa as well as on the track of TRACE A flight 15 over the South Atlantic. When using the Goddard Space Flight Center isentropic model, horizontal separations of greater than 1000 km occur for about 50% of the points when trajectories run with the ECMWF and NMC analyses are compared. Greater sensitivity to the input analysis differences is noted when trajectories are computed with the FSU kinematic model (separations exceed 1000 km for 75% of the points). The problem of meteorological uncertainty should be addressed with two approaches. There are large differences between both sets of analyses and the TRACE A soundings; this is also likely to be the case in other remote regions. Therefore we recommend that a test set of trajectories be computed with both sets of input data to quantify the uncertainty due to analysis differences. In addition, clusters of trajectories about the points of interest should be run to assess the uncertainty due to wind shear. These recommendations are applicable to any region of the globe with sparse observations. The companion paper [Fuelberg et al., this issue, part 2] addresses uncertainties due to trajectory technique.
A new method of deriving time-averaged tropospheric column ozone over the tropics using total ozone mapping spectrometer (TOMS) radiances: Intercomparison and analysis using TRACE A data
(AGU, 1996-10-01) Kim, J. H.; Hudson, R. D.; Thompson, Anne M.
Error analysis of archived total O3 from total ozone mapping spectrometer (TOMS) (version 6) presented in earlier studies [Hudson and Kim, 1994; Hudson et al., 1995] is extended to include scan angle effects. Daily total O3 maps for the tropics, from the period October 6–21, 1992, are derived from TOMS radiances following correction for these errors. These daily maps, averaged together, show a wavelike feature, which is observed in all latitude bands (10°N to 14°S), underlying sharp peaks which occur at different longitudes depending on the latitude. The wave pattern is used to derive both time-averaged stratospheric and tropospheric O3 fields. The nature of the wave pattern (stratospheric or tropospheric) cannot be determined with certainty due to missing data (no Pacific sondes, no lower stratospheric Stratospheric Aerosol and Gas Experiment (SAGE) ozone for 18 months after the Mt. Pinatubo eruption) and significant uncertainties in the corroborative satellite record in the lower stratosphere (solar backscattered ultraviolet (SBUV), microwave limb sounder (MLS)). However, the time-averaged tropospheric ozone field, based on the assumption that the wave feature is stratospheric, agrees within 10% with ultraviolet differential absorption laser Transport and Atmospheric Chemistry near the Equator-Atlantic) (TRACE A) O3 measurements from the DC-8 [Browell et al., this issue] and with ozonesonde measurements over Brazzaville, Congo (4°S, 15°W;), Ascension Island (8°S, 15°W), and Natal, Brazil (5.5°S, 35°W), for the period October 6–21, 1992. The derived background (nonpolluted) Indian Ocean tropospheric ozone amount, 26 Dobson units (DU), agrees with the cleanest African ozonesonde profiles for September–October 1992. The assumption of a totally tropospheric wave (flat stratosphere) gives 38 DU above the western Indian Ocean and 15–40% disagreements with the sondes. Tropospheric column O3 is high from South America to Africa, owing to interaction of dynamics with biomass burning emissions [Thompson et al., this issue (a, b)]. Comparison with fire distributions from advanced very high resolution radiometer (AVHHR) during October 1992 suggests that tropospheric O3 produced from biomass burning in South America and Africa dominates the O3 budget in the tropical southern hemisphere during the study period.