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  • GEOPHYSICS  (14)
  • 1990-1994  (14)
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  • 1
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    Episodic total ozone minima and associated effects on heterogeneous chemistry and lower stratospheric transport (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Three-dimensional model simulations are used to describe the January 31, 1989 ozone minihole over Stavanger, Norway. This minihole is typical of many transient events in the lower stratosphere that arise because of cyclonic-scale disturbances in the troposphere. Although the ozone reduction is a short-lived reversible dynamical event, through heterogeneous chemical processes there can be a significant transfer of chlorine from reservoir molecules to active radicals. This chemically perturbed air is defined as processed air, and it is found that a single event can produce enough processed air to reduce the HCl in the entire polar vortex. Chemical processing on clouds associated with transient events is shown to be a major source of processed air in the polar vortex in December before background temperatures are cold enough for more uniform heterogeneous conversion.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 97; D8, M
    Format: text
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  • 2
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    Application of a monotonic upstream-biased transport scheme to three-dimensional constituent transport calculations (1991)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The application of van Leer's scheme, a monotonic, upstream-biased differencing scheme, to three-dimensional constituent transport calculations is shown. The major disadvantage of the scheme is shown to be a self-limiting diffusion. A major advantage of the scheme is shown to be its ability to maintain constituent correlations. The scheme is adapted for a spherical coordinate system with a hybrid sigma-pressure coordinate in the vertical. Special consideration is given to cross-polar flow. The vertical wind calculation is shown to be extremely sensitive to the method of calculating the divergence. This sensitivity implies that a vertical wind formulation consistent with the transport scheme is essential for accurate transport calculations. The computational savings of the time-splitting method used to solve this equation are shown. Finally, the capabilities of this scheme are illustrated by an ozone transport and chemistry model simulation.
    Schlagwort(e): GEOPHYSICS
    Materialart: Monthly Weather Review (ISSN 0027-0644); 119; 2456-246
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    Three-dimensional simulations of wintertime ozone variability in the lower stratosphere (1991)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The evolution of ozone has been calculated for the winters of 1979 and 1989 using winds derived from the stratospheric data assimilation system STRATAN. The ozone fields calculated using this technique are found to compare well with satellite-measured fields for simulations of 2-3 months. This paper presents comparisons of model fields with both satellite and sonde measurements to verify that stratospheric transport processes are properly represented by this modeling technique. Attention is focused on the Northern Hemisphere middle and high latitudes at the 10-hPa level and below, where transport processes are most important to the ozone distribution. First-order quantities and derived budgets from both the model and satellite data are presented. By sampling the model with a limb-viewing satellite and then Kalman filtering the 'observations' of the model, it is shown that transient subplanetary-scale features that are essential to the ozone budget are missed by the satellite system.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 96; 5055-507
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Effect of solar proton events on the middle atmosphere during the past two solar cycles as computed using a two-dimensional model (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper investigates the effects of solar proton events (SPEs) on the middle atmosphere during the past two solar cycles (1963-1984), by examining changes in the production of odd nitrogen, NO(y), and ozone and using a proton energy degradation scheme to derive ion pair production rates. These calculations show that NO(y) is not substantially changed over a solar cycle by SPEs; significant SPEs last only 1-5 days, tend to occur near solar maximum, and are typically months to years apart, preventing a build up of SPE-produced NO(y). Fractional ozone changes are even smaller than the fractional NO(y) changes and are significant only for the August 1972 SPE. Ozone, like NO(y), returns to its ambient levels on time scales of several months to a year.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 95; 7417-742
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
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    Spatial and temporal variability of the extent of chemically processed stratospheric air (1991)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Simulations of the spatial and temporal variability of the extent of chemically processed air in the Arctic stratosphere have been carried out using a three-dimensional chemistry-transport model for the winters of 1979 and 1989. Chemically processed air is identified in the model as that in which the amounts of hydrogen chloride (HCl) calculated with parameterized loss for conditions appropriate to polar stratospheric cloud (PSC) formation are substantially smaller than those calculated in a model with gas phase chemistry only. It is seen that chemically processed air may be identified over much of the Arctic lower stratosphere from early January to late February, with HCl depletions being larger in 1989 than in 1979. Near the latitude of the Arctic circle, there is important spatial and temporal variability in the extent of chemically processed air. There is some evidence for transport to midlatitudes of processed air during these winters, but the HCl reductions are much smaller and more sporadic than those near the pole. At 62 and 42N, processed air is calculated to occur preferentially over the longitude regions from 60-120E and 270-330E.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 18; 29-32
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    The influence of polar heterogeneous processes on reactive chlorine at middle latitudes - Three dimensional model implications (1991)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Three-dimensional model calculations with the NASA/GSFC chemistry and transport model have been designed to consider the impact of heterogeneous processes occurring on polar stratospheric clouds (PSCs) in the Arctic vortex on the HCl distribution. By examining the HCl concentration for a calculation with PSCs relative to a calculation with gas phase chemistry only, the impact of polar processing on reactive chlorine species at middle latitudes is inferred. Results from the chemistry and transport model reproduce basic features of the ClO measurements (Toohey et al., 1991), which were made on the ferry flights of the ER-2 from Stavanger, Norway to Moffett Field, California via Wallops Island, Virginia on February 20 and 21, 1989. The model indicates that perturbed air which is contained within the polar vortex during winter is not homogeneously mixed, and that the ferry flights were made through air with the largest conversion of HCl to reactive chlorine that is seen at middle latitudes.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 18; 25-28
    Format: text
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  • 7
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    Wintertime nitric acid chemistry - Implications from three-dimensional model calculations (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A three-dimensional simulation of the evolution of HNO3 has been run for the winter of 1979. Winds and temperatures are taken from a stratospheric data assimilation analysis, and the chemistry is based on Limb Infrared Monitor of the Stratosphere (LIMS) observations. The model is compared to LIMS observations to investigate the problem of 'missing' nitric acid chemistry in the winter hemisphere. Both the model and observations support the contention that a nitric acid source is needed outside of the polar vortex and north of the subtropics. Observations suggest that HNO3 is not dynamically controlled in middle latitudes. The model shows that given the time scales of conventional chemistry, dynamical control is expected. Therefore, an error exists in the conventional chemistry or additional processes are needed to bring the model and data into agreement. Since the polar vortex is dynamically isolated from the middle latitudes, and since the highest HNO3 values are observed in October and November, a source associated solely with polar stratospheric clouds cannot explain the deficiencies in the chemistry. The role of heterogeneous processes on background aerosols is reviewed in light of these results.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 2696-270
    Format: text
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  • 8
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    Global three-dimensional constituent fields derived from profile data (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The success of three-dimensional simulations of stratospheric constituent variability depends critically on the initialization of the constituent fields within the global model. This paper describes a technique for generating global three-dimensional fields from vertical constituent proflies. The technique uses potential vorticity (q) and potential temperature (theta) to map the profiles onto the global domain. The profiles used here are obtained from a two-dimensional model calculation that reproduces the relationship between theta, q, N2O and O3 observed during the Airborne Arctic Stratospheric Expedition. The method is verified by comparison with satellite data, aircraft data, and model simulations.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 525-528
    Format: text
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  • 9
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    Stratospheric temperatures during AASE - Results from STRATAN (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Comparisons of temperatures from the research analysis STRATAN to radiosonde data, Meteorological Measurement System (MMS) data, and the National Meteorological Center (NMC) analyses are presented for the Airborne Arctic Stratospheric Expedition (AASE). The STRATAN analyses show consistent quality throughout AASE. The comparisons to MMS show that STRATAN more accurately represented low temperatures than NMC. This, coupled with forecast quality, show that STRATAN temperature fields are a valuable tool for diagnosing and forecasting polar stratospheric clouds.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 337-340
    Format: text
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  • 10
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    Three dimensional simulation of hydrogen chloride and hydrogen fluoride during the Airborne Arctic Stratospheric Expedition (1990)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Simulations of the evolution of stratospheric distributions of hydrogen chloride (HCl) and hydrogen fluoride (HF) have been carried out for the period of the Airborne Arctic Stratospheric Expedition (AASE) with a three-dimensional chemistry-transport model. Simulations were performed assuming only homogeneous gas phase chemistry for HF and both homogeneous gas phase and heterogeneous chemistry for HCl. Results show heterogeneous loss of HCl is needed to provide agreement with infrared column measurements. Estimates of the impact of heterogeneous loss on the global HCl distribution are obtained from the model. Reductions of HCl due to heterogeneous loss are calculated to be localized to regions of high vorticity, even after more than a month of integration.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 529-532
    Format: text
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