摘要:

Winter polar stratospheric nitric oxide (N2O) measurements made during two NASA polar aircraft field campaigns are used to evaluate the dynamics of the Geophysical Fluid Dynamics Laboratory's “SKYHI” general circulation model. SKYHI has 1° latitude by 1.2° longitude grid spacing and 40 vertical levels (up to 80 km) and prescribed N2O dissociation coefficients. The model has been integrated a total of 20 months, producing one Antarctic and two Arctic winters. The climatologies of these winters are compared with the known northern and southern hemisphere climatologies and to the meteorological conditions during the time of the field campaigns. The two Arctic SKYHI winters show considerable interannual variability. In the lower stratosphere, SKYHI realistically simulates the magnitude and variability of winds and temperatures both inside and outside the polar vortex and can produce a credible sudden warming. In the Antarctic the magnitude and variability of winds and temperatures around the polar vortex are quite realistic, but inside the vortex, temperatures are too low. Flight data from each mission have been averaged together to produce a contour map showing N2O morphology in and around the vortex. Because the N2O distribution in the lower stratosphere is under dynamical control, the mean N2O field can be used to interpret the dynamics of the polar stratosphere. At the Arctic vortex edge, AASE data show large gradients of N2O on isentropic surfaces. SKYHI vortex edge gradients are nearly as large, and model mixing ratios between 400 and 500 K (potential temperature) are similar to the observations. In the Antarctic, model mixing ratios are too high everywhere and the edge gradients are flatter than the observed gradients. The comparison of mean N2O fields suggests realistic wave activity in the SKYHI Arctic winter but inadequate wave activity in the SKYHI Antarctic w

ISSN:0148-0227    

DOI:10.1029/93JD02332

年代:1994

数据来源: WILEY

摘要:

Winter polar stratospheric nitrous oxide (N2O) measurements made during two NASA polar aircraft field campaigns provide a unique opportunity to evaluate the performance of the 1° latitude resolution version of the Geophysical Fluid Dynamics Laboratory's “SKYHI” general circulation model. This high‐resolution model has been integrated 20 months, producing one Antarctic and two Arctic winters. Power spectra of the dynamically controlled tracer N2O are used as a diagnostic of wave activity. Comparison of the spectra of SKYHI and the observations shows that the SKYHI Arctic winter lower stratosphere is dynamically active enough to generate realistic mesoscale tracer variability but that the SKYHI Antarctic has deficient variability at scales of 220–3000 km. Low‐pass filtering is applied to a new type of analysis that attempts to discriminate between different sources of atmospheric variability, to the extent that different sources are characterized by different timescales. The goal is to diagnose mesoscale sources of tracer variability in the model and in the observations and then to assess whether SKYHI generates variability for the right physical reasons. This analysis shows that variability from “slow” processes such as planetary wave breaking dominates and is generated in realistic amounts in the SKYHI Arctic winters. The SKYHI Antarctic vortex shows insufficient “debris” from planetary wave breaking at scales below 700 km. The balance between diabatic descent inside the vortex and wave breaking in the “surf zone” generates N2O gradients at the vortex edge in the model and the real atmosphere. Because the diabatic circulation is driven by wave activity, the strength of model wave activity diagnosed by the spectral analysis and the mean N2O gradients can be used to evaluate SKYHI's diabatic circulation and net tracer transport. In the Arctic, SKYHI temperatures, spectral results, and realistic N2O gradients at the vortex edge suggest a reasonable diabatic meridional circulation and transport. Antarctic spectral results, low vortex temperatures, and flatter N2O gradients at the edge all support the conclusion that the diabatic circulation and wave activity in the model southern

ISSN:0148-0227    

DOI:10.1029/94JD00044

年代:1994

数据来源: WILEY

摘要:

The stratospheric aerosol measurement II, stratospheric aerosol and gas experiment (SAGE) I, and SAGE II series of solar occultation satellite instruments were designed for the study of stratospheric aerosols and gases and have been extensively validated in the stratosphere. They are also capable, under cloud‐free conditions, of measuring the extinction due to aerosols in the troposphere. Such tropospheric extinction measurements have yet to be validated by appropriate lidar and in situ techniques. In this paper published atmospheric aerosol optical depth measurements, made from high‐altitude observatories during volcanically quiet periods, have been compared with optical depths calculated from local SAGE I and SAGE II extinction profiles. Surface measurements from three such observatories have been used, one located in Hawaii and two within the continental United States. Data have been intercompared on a seasonal basis at wavelengths between 0.5 and 1.0 μm and found to agree within the range of measurement errors and expected atmospheric variation. The mean rms difference between the optical depths for corresponding satellite and surface measured data sets is 29%, and the mean ratio of the optical depths is

ISSN:0148-0227    

DOI:10.1029/94JD00167

年代:1994

数据来源: WILEY

摘要:

Ground‐based measurements of the solar transmission and sky radiance in a horizontal plane through the Sun are taken in several geographical regions and aerosol types: dust in a desert transition zone in Israel, sulfate particles in Eastern and Western Europe, tropical aerosol in Brazil, and mixed continental/maritime aerosol in California. Stratospheric aerosol was introduced after the eruption of Mount Pinatubo in June 1991. Therefore measurements taken before the eruption are used to analyze the properties of tropospheric aerosol; measurements from 1992 are also used to detect the particle size and concentration of stratospheric aerosol. The measurements are used to retrieve the size distribution and the scattering phase function at large scattering angles of the undisturbed aerosol particles. The retrieved properties represent an average on the entire atmospheric column. A comparison between the retrieved phase function for a scattering angle of 120°, with phase function predicted from the retrieved size distribution, is used to test the assumption of particle homogeneity and sphericity in radiative transfer models (Mie theory). The effect was found to be small (20%±15%). For the stratospheric aerosol (sulfates), as expected, the phase function was very well predicted using the Mie theory. A model with a power law size distribution, based on the spectral dependence of the optical thickness, a, cannot estimate accurately the phase function (up to 50% error for λ = 0.87 μm). Before the Pinatubo eruption the ratio between the volumes of sulfate and coarse particles was very well correlated with α. The Pinatubo stratospheric aerosol destroyed this correlation. The aerosol optical properties are compared with analysis of the size, shape, and composition of the individual particles by electron microscopy of in situ samples. The measured volume size distributions before the injection of stratospheric aerosol consistently show two modes, sulfate particles withrm0.7 μm. The “window” in the tropospheric aerosol in this radius range was used to observe a stable stratospheric aerosol in 1992, withrm∼ 0.5 μm. A combination of such optical thickness and sky measurements can be used to assess the direct forcing and the climatic impact of aerosol. Systematic inversion for the key aerosol types (sulfates, smoke, dust, and maritime aerosol) of the size distribution and phase function can give the relationship between the aerosol physical and optical properties that can be used to compute the radiative forcing. This forcing can be validated in dedicated fi

ISSN:0148-0227    

DOI:10.1029/94JD00229

年代:1994

数据来源: WILEY

摘要:

Land surface climatologies averaged over the last 5 years of 10‐year seasonal cycle integrations of the National Center for Atmospheric Research community climate model 2 (CCM2) with the Biosphere‐Atmosphere Transfer Scheme (BATS) land surface option configured for R15 and T42 resolutions were compared. Both simulations had a large warm‐temperature bias over northern hemisphere land regions in July. The CCM2 without BATS has a similar bias, which BATS, with its interactive hydrology, accentuated. Both simulations had too much precipitation, which is also a feature of CCM2 without BATS. Most differences in continental‐averaged hydrologic and surface energy fluxes between the R15 and T42 simulations were minor for January and July (<0.4 mm d−1and<11 W m−1). Only 5 of 14 continental‐scale comparisons showed larger differences. In two of these, differences in land surface hydrology and energy exchange between the R15 and T42 simulations were related to precipitation differences, possibly from changes in the cloud fraction parameterization of CCM2 in its R15 and T42 configurations. The spatial resolution of the model was also important for the Mississippi Basin, where the T42 model was hotter and drier than the R15 model. These analyses show that improved spatial resolution does not necessarily result in continental‐averaged land surface climatologies substantially different from those of lower‐resolution models but that the improved resolution can be important a

ISSN:0148-0227    

DOI:10.1029/94JD00424

年代:1994

数据来源: WILEY

摘要:

A 10‐year atmospheric simulation was run using the European Centre for Medium‐Range Weather Forecasts (cycle 36) model for the decade 1979–1988. The observed monthly mean sea surface temperatures were specified in the integration. This simulation was part of the Atmospheric Model Intercomparison Project. From the output of the model, simulated monthly mean microwave sounding unit (MSU) temperatures were computed. The anomalies of these monthly MSU temperatures were then compared to the observations and to previously published works. The results are as follows: (1) The model displays similar patterns of MSU/sea surface temperature (SST) correlations to the data of Trenberth et al. (1992). These patterns are formed by spatial variations in the SST signal and by the varying response of the atmosphere to SST changes. (2) The model evidently underestimates the air‐sea exchange of heat in the region of the Kuroshio current. (3) The point correlation patterns in the MSU temperatures for the 10‐year period are strongly influenced El Niño‐Southern Oscillation (ENSO) events in this decade. (4) The dominance of the signal of the 1982/1983 and 1986/1987 events makes it risky to extend the relationships seen in this decade to other, less active periods. (5) The model tends to produce MSU anomalies in good accord with the observations only during ENSO western Pacific

ISSN:0148-0227    

DOI:10.1029/94JD00546

年代:1994

数据来源: WILEY

摘要:

The amplification of small initial errors in connection with mesoscale atmospheric variability is studied on a simplified thermal convection model. It is found that when the system is perturbed uniformly over the physical space, the initial regime of error dynamics follows a pathway far from the traditional exponential function whose rate is the largest positive Lyapunov exponent. It comprises two stages: (1) a transient decrease of the initial error as a result of the displacement of the system out of its attractor and (2) a superexponential increase whose origin is in the multifractal character of the attractor. Numerical experiments in which the initial error is introduced selectively in a particular scale reveal that perturbations at larger scales grow faster than those at the intermediate and small scales. A qualitative explanation of this unexpected behavior based on intrinsic properties of the dynamics such as the local Lyapunov vectors is advanced.

ISSN:0148-0227    

DOI:10.1029/94JD00248

年代:1994

数据来源: WILEY

摘要:

A novel method for remote optical diagnostics of the atmosphere at heights 30–60 km is proposed. The method relies on exciting atoms and molecules of minority species by electron impact during and following an ionizing microwave pulse injected from a focused ground‐based transmitter. Free electrons produced in the breakdown region are the exciting agents for the atmospheric target molecules. The mixing ratio of the minority species can then be measured by either detecting the direct emission from allowed transitions or by utilizing lidar techniques to measure the excitation level of metastable states. Computer simulations of the intensity of the expected emission, based on kinetic theory of air breakdown, are presented. It is shown that mixing ratios below particle per trillion can be detected using microwave heaters with state of the art effective radiation power and modern detection technol

ISSN:0148-0227    

DOI:10.1029/93JD03196

年代:1994

数据来源: WILEY

摘要:

Modeling studies suggest that polar regions play a major role in modulating the Earth's climate and that they may be more sensitive than lower latitudes to climate change. Until recently, however, data from meteorological stations poleward of 70° have been sparse, and consequently, our understanding of air‐sea‐ice interaction processes is relatively poor. Satellite‐borne sensors now offer a promising opportunity to observe polar regions and ultimately to improve parameterizations of energy transfer processes in climate models. This study focuses on the application of the TIROS‐N operational vertical sounder (TOVS) to sea‐ice‐covered regions in the nonmelt season. TOVS radiances are processed with the improved initialization inversion (“3I”) algorithm, providing estimates of layer‐average temperature and moisture, cloud conditions, and surface characteristics at a horizontal resolution of approximately 100 km × 100 km. Although TOVS has flown continuously on polar‐orbiting satellites since 1978, its potential has not been realized in high latitudes because the quality of retrievals is often significantly lower over sea ice and snow than over other surfaces. The recent availability of three Arctic data sets has provided an opportunity to validate TOVS retrievals: the first from the Coordinated Eastern Arctic Experiment (CEAREX) in winter 1988/1989, the second from the LeadEx field program in spring 1992, and the third from Russian drifting ice stations. Comparisons with these data reveal deficiencies in TOVS retrievals over sea ice during the cold season; e.g., ice surface temperature is often 5 to 15 K too warm, microwave emissivity is approximately 15% too low at large view angles, clear/cloudy scenes are sometimes misidentified, and low‐level inversions are often not captured. In this study, methods to reduce these errors are investigated. Improvements to the ice surface temperature retrieval have reduced rms errors from approximately 7 K to 3 K; correction of microwave (50 GHz) brightness temperatures for view angle dependence now allows the surface type (open water versus sea ice) to be determined; modifications to the clear/cloud tests have improved cloud detection over sea ice, especially where it is inhomogeneous; and improved surface temperature estimates have resulted in more successful diagnoses of low‐level stratification. Applications of improved retrievals to studies of the Arctic energy budget are encouraging. Preliminary calculations of air‐ice stress vectors, 10‐m wind speed, and horizontal advection of he

ISSN:0148-0227    

DOI:10.1029/94JD00166

年代:1994

数据来源: WILEY

摘要:

Infrared radiative excitation in non‐local thermodynamic equilibrium (non‐LTE) regions of the Earth's atmosphere for thev3‐mode vibrationally excited states of CO2under sunlit conditions and the resulting 4.3‐μm limb radiance are calculated using a line‐by‐line (LBL) radiative transfer model. Excited‐state population densities and the corresponding vibrational temperature profiles are calculated for the important emitting states using a model which includes radiative absorption and emission as well as various collisional processes. The quenching of O(1D) by N2has a greater impact on these population densities than has been previously reported in the literature. Integrated radiance in a limb view for the 4.3‐μm bands is calculated from the model and compared with sunlit earthlimb measurements obtained by the Spectral Infrared Rocket Experiment (SPIRE). Solar pumping is the dominant excitation process for the 4.3‐μm emitting states in the daytime. The major contribution to the total limb radiance for tangent heights of 55–95 km is made by the fluorescent states at approximately 3600 cm−1which absorb sunlight at 2.7 μm and then emit preferentially at 4.3 μm. The predicted radiance is in good agreement with the SPIRE measurements for all tangent heights in the 50‐ to 130‐km range. This is the first detailed comparison of results of a full line‐by‐line non‐LTE radiative transfer calculation

ISSN:0148-0227    

DOI:10.1029/94JD00315

年代:1994

数据来源: WILEY