An imaging passive microwave radiometer for precipitation retrieval and mesoscale storm system studies
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Galliano, J. A.↗
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Results for “Mesoscale”
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Mesoscale air-sea interactions related to tropical and extratropical storms in the Gulf of Mexico
Observations of the lower atmosphere of the northwestern Gulf of Mexico from November 1982 to mid-February 1983 were studied in which seven significant cyclones were generated in the northwestern gulf. It was found that all seven storms occurred when the vorticity correlate of the horizontal air temperature difference was about 3-5 C above the climatological mean difference. It is shown that a maximum in the frequency of tropical storms within the Gulf of Mexico exists some 275 km south of the Mississippi delta at 27 deg N, 90 deg W. This maximum is a result of only those storms which originate within the gulf. Two plausible effects of the Loop Current and its rings on tropical storms are discussed. One is that these ocean features are large and consolidated heat and moisture sources from which a nearby slowly moving atmospheric disturbance can extract energy. The second is that of the cyclonic vorticity that can be generated in the lower atmosphere by such oceanographic features.
Lewis, James K.↗
Distribution of Reynolds stress carried by mesoscale variability in the Antarctic Circumpolar Current
Satellite altimeter data collected by the Geosat Exact Repeat Mission were used to investigate turbulent stress resulting from the variability of surface geostrophic currents in the Antarctic Circumpolar Current. The altimeter measured sea level along the subsatellite track. The variability of the along-track slope of sea level is directly proportional to the variability of surface geostrophic currents in the cross-track direction. Because the grid of crossover points is dense at high latitudes, the satellite data could be used for mapping the temporal and spatial variability of the current. Two and a half years of data were used to compute the statistical structure of the variability. The statistics included the probability distribution functions for each component of the current, the time-lagged autocorrelation functions of the variability, and the Reynolds stress produced by the variability. The results demonstrate that stress is correlated with bathymetry. In some areas the distribution of negative stress indicate that eddies contribute to an acceleration of the mean flow, strengthening the hypothesis that baroclinic instability makes important contributions to strong oceanic currents.
Johnson, Thomas J.↗
A statistical analysis of mesoscale rainfall as a random cascade
The paper considers the random cascade theory for spatial rainfall. Particular attention was given to the following four areas: (1) the relationship of the random cascade theory of rainfall to the simple scaling and the hierarchical cluster-point-process theories, (2) the mathematical foundations for some of the formalisms commonly applied in the develpment of statistical cascade theory, (3) the empirical evidence for a random cascade theory of rainfall, and (4) the way of using data for making estimates of parameters and for making statistical inference within this theoretical framework. An analysis of space-time rainfall data is presented. Cascade simulations are carried out to provide a comparison with methods of analysis that are applied to the rainfall data.
Gupta, Vijay K.↗
A nonreflecting upper boundary condition for anelastic nonhydrostatic mesoscale gravity-wave models
A sponge layer is formulated to prevent spurious reflection of vertically propagating quasi-stationary gravity waves at the upper boundary of a two-dimensional numerical anelastic nonhydrostatic model. The sponge layer includes damping of both Newtonian-cooling type and Rayleigh-friction type, whose coefficients are determined in such a way that the reflectivity of wave energy at the bottom of the layer is zero. Unlike the formulations in earlier studies, our formulation includes the effects of vertical discretization, vertical mean density variation, and nonhydrostaticity. This sponge formulation is found effective in suppressing false downward reflection of waves for various types of quasi-stationary forcing.
Kim, Young-Joon↗
Upper tropospheric ozone production following mesoscale convection during STEP/EMEX
The chemistry and dynamics of a convective system observed on February 2, 1987 in the EMEX and STEP campaigns are analyzed. Chemical and thermodynamic profiles in undisturbed air near the EMEX 9 system indicate that the troposphere was well mixed by previous convection. As a consequence there was little direct transport from the boundary layer to the upper troposphere and air transported upward was detrained throughout the middle and upper troposphere. There was minimal effect on O3 production. Other convective complexes located 800-900 km upstream produced greater perturbations on trace gas profile immediately below the tropopause. Ozone production was reduced by about 0.25 ppbv/d at these altitudes, representing a reduction in P(O3) of 15-20 percent over the column from 14.5 to 17 km. P(O3) from 12 to 17 km in a region distant from active convection and subject to lightning was 2-3 times higher than it would have been without lightning.
Pickering, Kenneth E.↗
Mesoscale Lightning
This video tape addresses ongoing lightning research and how data is valuable to upcoming projects.
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Comparison and analysis of aircraft measurements and mesoscale atmospheric chemistry model simulations of tropospheric ozone
The Regional Acid Deposition Model (RADM) has been applied to several of the field experiments which were part of the Acid Models Operational and Diagnostic Evaluation Study (Acid MODES). The experiment which was of particular interest with regards to ozone photochemistry involved horizontal zig-zag flight patterns (ZIPPER) over an area from the eastern Ohio River valley to the Adirondacks of New York. Model simulations by both the standard resolution RADM (delta x = 80 km) and the nested grid RADM (delta x = 26.7 km) compare well to measurements in the low emission regions in central Pennsylvania and upstate New York, but underestimate in the high emission upper Ohio River valley. The nested simulation does considerably better, however, than the coarse grid simulation in terms of horizontal pattern and concentration magnitudes. Analysis of NO(x) and HO(x) concentrations and photochemical products rates of ozone show that the model's response to large point source emissions is very unsystematic both spatially and temporally. This is due to the models instability to realistically simulate the small scale (subgrid) gradients in precursor concentrations in and around large point source plumes.
Pleim, Jonathan E.↗
High-resolution satellite imagery for mesoscale meteorological studies
In this article high-resolution satellite imagery from a variety of meteorological and environmental satellites is compared. Digital datasets from Geostationary Operational Environmental Satellite (GOES), National Oceanic and Atmospheric Administration (NOAA), Defense Meteorological Satellite Program (DMSP), Landsat, and Satellite Pour l'Observation de la Terre (SPOT) satellites were archived as part of the 1990 Hawaiian Rainband Project (HaRP) and form the basis of the comparisons. During HaRP, GOES geostationary satellite coverage was marginal, so the main emphasis is on the polar-orbiting satellites.
Johnson, David B.↗
Reconstruction of the Mesoscale Velocity Shear Seaward of Coastal Upwelling Regions from the Refraction of the Surface Wave Field
The objective of this project is to study fronts that develop at the boundary between cold water recently upwelled to the surface through Ekman divergence, and warmer surrounding waters. This specific objective was suggested by studying the small scale structure of upwelling fronts (coastal, island, and equatorial) through shipboard surveys and infrared satellite images. Constraints on the shuttle equator crossing imposed by other land sites precluded a coverage of the area targeted in the initial SIR-C proposal, the California Current. The site was then relocated to the Equatorial Pacific upwelling tongue, that can be satisfactorily imaged for a wide range of longitudes of the equator crossing. Some limited data was nevertheless obtained over coastal upwelling off California in 1989, using the JPL AIRSAR in multifrequency mode, and over island upwelling off Hawaii in 1990, using the radar in along-track interferometric mode.
Flament, Pierre↗
Mesoscale Variability in SUCCESS Data
Analysis of meteorological, chemical, and microphysical data from the airborne SUCCESS mission is reported. Careful analysis of the complex DC-8 flight pattern of May 2, 1996 reveals 19 linear or nearly linear flight segments within six main geographical areas, which we have analyzed. Significant mountain wave activity is revealed in the data from the MMS and MTP instruments on the DC-8, which resembles previous observations of mountain wave structures near Boulder, CO. Strong mountain-wave-induced upwelling downwind of the Rockies is noted. Turbulence is also noted in regions of the mountain wave consistent with overturning near the tropopause. Zonal winds recorded on the ER-2 are shown to consistent with mountain wave breaking at or near critical levels in the stratosphere, consistent with the strong turbulence reported by the pilot during the ER-2 flight. Those observations have been supported with spectral analyses and modeling studies. "Postcasts" of mountain wave activity on May 2, 1996, using the Naval Research Laboratory Mountain Wave Forecast Model (NRL/MWFM) predicts both strong mountain wave activity near the tropopause (as measured by the DC-8) and strong mountain-wave-induced turbulence in the stratosphere (as encountered by the ER-2). Two-dimensional simulations of fluid flow over topography reveal similar isentropic structures to observations.
Eckermann, Stephen D.↗
Analysis of a Small Vigorous Mesoscale Convective System in a Low-Shear Environment: Formation, Echo Structure and Lightning Behavior - Pt. 1
The precipitation output was highly variable due to the transient nature of the intense convective elements. This result is attributed to the high Richardson number (175) of the environment, which is much higher than that of the typical MCS environment. The development of the stratiform precipitation was accomplished locally (in situ), and not be advection of from the convective region. In situ charging of the stratiform region is also supported by the observations.
Knupp, Kevin↗
Mesoscale to Synoptic Scale Cloud Variability
The atmospheric circulation and its interaction with the oceanic circulation involve non-linear and non-local exchanges of energy and water over a very large range of space and time scales. These exchanges are revealed, in part, by the related variations of clouds, which occur on a similar range of scales as the atmospheric motions that produce them. Collection of comprehensive measurements of the properties of the atmosphere, clouds and surface allows for diagnosis of some of these exchanges. The use of a multi-satellite-network approach by the International Satellite Cloud Climatology Project (ISCCP) comes closest to providing complete coverage of the relevant range space and time scales over which the clouds, atmosphere and ocean vary. A nearly 15-yr dataset is now available that covers the range from 3 hr and 30 km to decade and planetary. This paper considers three topics: (1) cloud variations at the smallest scales and how they may influence radiation-cloud interactions, and (2) cloud variations at "moderate" scales and how they may cause natural climate variability, and (3) cloud variations at the largest scales and how they affect the climate. The emphasis in this discussion is on the more mature subject of cloud-radiation interactions. There is now a need to begin similar detailed diagnostic studies of water exchange processes.
Rossow, William B.↗
Ocean Turbulence: Mesoscale Modeling in Isopycnal Coordinates the role of the Spectrum of Vertical Shear - Part 4
We study the tracer subgrid term in isopycnal coordinates, S(sub I). We employ two ingredients: the experimental data on vertical spectra of ocean turbulence measured by Gargett et al.(1981) and the stochastic approach recently developed by Dukowicz and Smith (1997). Our result confirms that S(sub I) is made of two parts: an advection and a diffusion term. However, the tracer bolus velocity u** consists of two terms u** = u(sub 1) + u(sub 2) while in the GM model there is only a term related to u(sub 1) which is shown to be: u(sub 1) = k(bar-q)(sup -1)(delta)(sub rho) where bar-q is the thickness weighted average potential vorticity, a result in agreement with the recent suggestions by Treguier et al. (1997), Lee et al. (1997) and Greatbatch (1998). The second component u(sub 2) IS new. We compute it in the geostrophic approximation using the Gargett et al. data (1981) on ocean vertical turbulence. We find that u(sub 2) much greater than u(sub 1) and that u(sub 2) is orthogonal to u(sub 1).
Canuto, V. M.↗
Investigation of Mesoscale Variability in Convective Boundary Layer Development Using LASE
Throughout this research effort we have analyzed data collected from the Southern Great Plains 1997 (SGP) experiment to evaluate terms in the budget of water vapor in the atmospheric boundary layer (ABL). The analysis is centered on using data obtained from the Lidar Atmospheric Sensing Experiment (LASE) downward-looking differential absorption lidar (DIAL) that was flown on the NASA-P3 aircraft. The DIAL is able to measure vertical profiles of water vapor, as well as aerosol backscatter, throughout the ABL. Initial work on using the DIAL is summarized in the attached meeting preprint, which discusses results from a segment of the 12 July 1997 flight. Additional analysis has been carried out using both the DIAL data and in situ measurements to obtain more complete and detailed estimates of terms in the ABL water vapor budget. This includes data from the Canadian National Research Council Twin Otter aircraft, as well as from a spectrum of surface-based instruments. This work is expected to lead to a refereed article planned for submission to the Journal.
Lenschow, Donald H.↗
Mesoscale Convective Systems in SCSMEX: Simulated by a Regional Climate Model and a Cloud Resolving Model
A Regional Land-Atmosphere Climate Simulation (RELACS) System is being developed and implemented at NASA Goddard Space Flight Center. One of the major goals of RELACS is to use a regional scale model with improved physical processes, in particular land-related processes, to understand the role of the land surface and its interaction with convection and radiation as well as the water and energy cycles in Indo-China/South China Sea (SCS)/China, North America and South America. The Penn State/NCAR MM5 atmospheric modeling system, a state of the art atmospheric numerical model designed to simulate regional weather and climate, has been successfully coupled to the Goddard Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) land surface model, PLACE allows for the effect A vegetation, and thus important physical processes such as evapotranspiration and interception are included. The PLACE model incorporates vegetation type and has been shown in international comparisons to accurately predict evapotranspiration and runoff over a wide variety of land surfaces. The coupling of MM5 and PLACE creates a numerical modeling system with the potential to more realistically simulate the atmosphere and land surface processes including land-sea interaction, regional circulations such as monsoons, and flash flood events. RELACS has been used to simulate the onset of the South China Sea Monsoon in 1986, 1991 and 1998. Sensitivity tests on various land surface models, cumulus parameterization schemes (CPSs), sea surface temperature (SST) variations and midlatitude influences have been performed. These tests have indicated that the land surface model has a major impact on the circulation over the South China Sea. CPSs can effect the precipitation pattern while SST variation can effect the precipitation amounts over both land and ocean. RELACS has also been used to understand the soil-precipitation interaction and feedback associated with a flood event that occurred in and around China's Yantz River during 1998. The exact location (region) of the flooding can be effected by the soil-rainfall feedback. Also, the Goddard Cumulus Ensemble (GCE) model which allows for realistic moist processes as well as explicit interactions between cloud and radiation, and cloud and surface processes will be used to simulate convective systems associated with the onset of the South China Sea Monsoon in 1998. The GCE model also includes the same PLACE and radiation scheme used in the RELACS. A detailed comparison between the results from the GCE model and RELACS will be performed.
Tao, W.-K.↗
A Study of the Response of Deep Tropical Clouds to Mesoscale Processes: Modeling Strategies and Simulations of TOGA-COARE Convective Systems - Part 1
Interactions between deep tropical clouds over the western Pacific warm pool and the larger-scale environment are key to understanding climate change. Cloud models are an extremely useful tool in simulating and providing statistical information on heat and moisture transfer processes between cloud systems and the environment, and can therefore be utilized to substantially improve cloud parameterizations in climate models. In this paper, the Goddard Cumulus Ensemble (GCE) cloud-resolving model is used in multi-day simulations of deep tropical convective activity over the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). Large-scale temperature and moisture advective tendencies, and horizontal momentum from the TOGA-COARE Intensive Flux Array (IFA) region, are applied to the GCE version which incorporates cyclical boundary conditions. Sensitivity experiments show that grid domain size produces the largest response to domain-mean temperature and moisture deviations, as well as cloudiness, when compared to grid horizontal or vertical resolution, and advection scheme. It is found that a minimum grid-domain size of 500 km is needed to adequately resolve the convective cloud features. The control experiment shows that the atmospheric heating and moistening is primarily a response to cloud latent processes of condensation/evaporation, and deposition/sublimation, and to a lesser extent, melting of ice particles. Air-sea exchange of heat and moisture is found to be significant, but of secondary importance, while the radiational response is small. The simulated rainfall and atmospheric heating and moistening, agrees well with observations, and performs favorably to other models simulating this case.
Johnson, Daniel E.↗
A study of heavy precipitation events in Taiwan during 10-13 August, 1994: mesoscale model simulations
Heavy rainfall occurred over the western side of Taiwan's complex terrain from August 10 to 13, 1994 after Typhoon Doug moved northward from the East China Sea into Taiwan and on towards the Yellow Sea. On August 10, most of the rainfall fell over sloped areas. The heaviest daily rainfall totals were in excess of 200 mm over southwestern as well as central Taiwan. However, not much rainfall occurred over northern Taiwan. The lack of rainfall over northern Taiwan also occurred on August 11, 12 and 13. The larger rainfall amounts shifted westward from the sloped areas on August 10 toward lower terrain on August 11. On August 12 and 13, most of the higher rainfall amounts were found over the coastal area in southwestern Taiwan. Notably, about 300 to 400 mm per day fell over the coastal area in southwest Taiwan on August 12 and 13. The distribution of rainfall amount was different on August 10 and 11 (termed as Case 1) compared to August 12 and 13 (termed as Case 2). The environmental situation and precipitation characteristics are analyzed using EC/TOGA data, ground-based radar data, surface rainfall patterns, surface wind data, and upper air soundings. Chen at al. (2001) also categorized the precipitation pattern into two types, propagating and quasi-stationary. For the propagating type of precipitation, rainrates increased or remained the same as systems went from the plains to mountainous regions. With the quasi-stationary type of precipitation, however, rainrates decreased as precipitation propagated across the plains and into the mountains. The focus of this study is to understand what causes the h1aher amounts of rainfall over Taiwan, and what factors influence where the higher amounts of rainfall will occur, over sloped areas or over coastal areas.
Tao, W.-K.↗