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NASA NTRS1991

Combined flatland ST radar and digital-barometer network observations of mesoscale processes

The paper describes a six-station digital-barometer network centered on the Flatland ST radar to support observational studies of gravity waves and other mesoscale features at the Flatland Atmospheric Observatory in central Illinois. The network's current mode of operation is examined, and a preliminary example of an apparent group of waves evident throughout the network as well as throughout the troposphere is presented. Preliminary results demonstrate the capabilities of the current operational system to study wave convection, wave-front, and other coherent mesoscale interactions and processes throughout the troposphere. Unfiltered traces for the pressure and horizontal zonal wind, for days 351 to 353 UT, 1990, are illustrated.

Clark, W. L.↗

NASA NTRS1991

Kinematic and precipitation structure of a small, long-lived mesoscale convective system

A comprehensive analysis using conventional single Doppler radar analyses, analysis of multiparameter (CP-2) data, network sounding and surface data, and GOES satellite data is presented to characterize the internal kinematic and precipitation structure of a small, long-lived mesoscale convective system. The data pertain to the Cooperative Huntsville Meteorological experiment conducted over northern Alabama and central Tennessee during June and July of 1986. The mesoscale convective system pulsations visible in the IR patterns were associated with the development of closely interacting aggregates of convective elements. The aggregates were about 20 km in diameter, attained echo tops of about 13 km, and were dominated by a single relatively intense convective element. The measured difference in radial velocity across the upper portion of these elements was about 20 m/s over a distance of about 10 km.

Knupp, Kevin R.↗

NASA NTRS1993

The radiative budgets of a tropical mesoscale convective system during the EMEX-STEP-AMEX experiment. I - Observations. II - Model results

The spatial radiation heating budget associated with tropical mesoscale convective systems (MCSs) is studied and the change of this heating/budget throughout the life cycle of such a cloud system is investigated. The movements of an EMEX 9 cloud cluster are described. The vertical structure of the cluster contains two types of imbedded convection: an upright vertical structure and a pronounced rearward slope with vertical extent of 14.5 km or more and a horizontal scale of about 40 km. The cloud base and cloud top altitude in the stratiform region are of the order of 4.8 km and 15-16 km, respectively. The upward and downward solar flux profiles suggest very little solar heating in these regions. A tropical MCS that occurred during the EMEX Mission 9 is simulated, and the simulation is shown to broadly agree with the observations. The simulation results, which are reported in detail, show how tropical mesoscale cloud systems provide an effective radiative heat source for the tropical atmosphere.

Wong, Takmeng↗

NASA NTRS1985

Use of ground-based wind profiles in mesoscale forecasting

A brief review is presented of recent uses of ground-based wind profile data in mesoscale forecasting. Some of the applications are in real time, and some are after the fact. Not all of the work mentioned here has been published yet, but references are given wherever possible. As Gage and Balsley (1978) point out, sensitive Doppler radars have been used to examine tropospheric wind profiles since the 1970's. It was not until the early 1980's, however, that the potential contribution of these instruments to operational forecasting and numerical weather prediction became apparent. Profiler winds and radiosonde winds compare favorably, usually within a few m/s in speed and 10 degrees in direction (see Hogg et al., 1983), but the obvious advantage of the profiler is its frequent (hourly or more often) sampling of the same volume. The rawinsonde balloon is launched only twice a day and drifts with the wind. In this paper, I will: (1) mention two operational uses of data from a wind profiling system developed jointly by the Wave Propagation and Aeronomy Laboratories of NOAA; (2) describe a number of displays of these same data on a workstation for mesoscale forecasting developed by the Program for Regional Observing and Forecasting Services (PROFS); and (3) explain some interesting diagnostic calculations performed by meteorologists of the Wave Propagation Laboratory.

Schlatter, Thomas W.↗

NASA NTRS1985

Current issues concerning the representativeness and utility of cloud drift winds in mesoscale meteorology

High-resolution cloud motion wind (CMW) data sets obtained from geostationary satellites for approximately the past decade have been used for the purpose of estimating mesoscale wind fields in various research studies. Yet there remains much controversy surrounding the proper interpretation and use of the resultant wind vector and kinematic fields. This paper is concerned with: (1) how representative are cloud draft winds of actual ambient air motions; and (2) what is the degree of practical usefulness of CMW fields for both mesoscale analysis and as input to numerical weather prediction models.

Koch, Steven E.↗

NASA NTRS1993

Waves and mesoscale features in the marginal ice zone

Ocean-ice interaction processes in the Marginal Ice Zone (MIZ) by waves and mesoscale features, such as upwelling and eddies, are studied using ERS-1 Synthetic Aperture Radar (SAR) imagery and wave-ice interaction models. Satellite observations of mesoscale features can play a crucial role in ocean-ice interaction study.

Liu, Antony K.↗

NASA NTRS1993

Chemistry on the mesoscale: Modeling and measurement issues

The topics covered include the following: Regional Acid Deposition Model (RADM) -- a coupled chemistry/mesoscale model; convection in RADM; unresolved issues for mesoscale modeling with chemistry -- nonprecipitating clouds; unresolved issues for mesoscale modeling with chemistry -- aerosols; tracer studies with Goddard Cumulus Ensemble Model (GCEM); field observations of trace gas transport in convection; and photochemical consequences of convection.

Thompson, Anne↗

NASA NTRS1993

Martian mesoscale circulations induced by variations in surface optical and thermal characteristics: A numerical study

According to Mariner 9 and Viking observations the surface albedo and the thermal inertia of Mars' surface vary substantially, and fairly large gradients also occur. The Syrtis Major region is bounded in the west by high-albedo cratered terrain and in the east by Isidis Planitia, a high-albedo plateau. Sinus Meridiani, centered at 0 degrees W 5 degrees S, is almost surrounded by higher albedo regions with sharp boundaries, and Acidalia Planitia, between 10 and 50 degrees W and north of 35 degrees N, has sharp albedo boundaries to the east and west. Observational and modeling studies, e.g., on Australian dry salt lake coasts, have shown that discontinuities and gradients in surface properties can induce mesoscale circulations. We have used a version of the DMUH mesoscale model to simulate atmospheric circulations induced by variations in the reflectivity and in the thermal inertia of the martian surface.

Siili, Tero↗

NASA NTRS1994

Predicting and explaining the movement of mesoscale oceanographic features using CLIPS

The Naval Research Laboratory has developed an oceanographic expert system that describes the evolution of mesoscale features in the Gulf Stream region of the northwest Atlantic Ocean. These features include the Gulf Stream current and the warm and cold core eddies associated with the Gulf Stream. An explanation capability was added to the eddy prediction component of the expert system in order to allow the system to justify the reasoning process it uses to make predictions. The eddy prediction and explanation components of the system have recently been redesigned and translated from OPS83 to C and CLIPS and the new system is called WATE (Where Are Those Eddies). The new design has improved the system's readability, understandability and maintainability and will also allow the system to be incorporated into the Semi-Automated Mesoscale Analysis System which will eventually be embedded into the Navy's Tactical Environmental Support System, Third Generation, TESS(3).

Bridges, Susan↗

NASA NTRS1995

The importance of mesoscale circulations generated by subgrid-scale landscape heterogeneities in general circulation models

A mesoscale atmospheric model was used to evaluate the impact of subgrid-scale landscape discontinuities on the vertical profiles of resolved temperature, moisture, and moist static energy in the planetary boundary layer (PBL) of general circulation models (GCMs). These profiles were produced with a 3D version of the model (using a horizontal grid resolution of 7.5 km and 13 vertical layers in the PBL) by averaging horizontally the various atmospheric variables over a 180 x 180 sq km domain-about the size of the horizontal domain represented by a single grid element in a GCM. They were compared to corresponding vertical profiles produced with a 1D version of the model, which simulates the PBL, as in a GCM, over a single horizontal grid element. Differences obtained between the horizontally averaged atmospheric variables produced with the 3D simulations and the 1D simulations emphasize the impact of subgrid-scale landscape discontinuities on GCM-resolved variables. Various types of landscape discontinuities, characterized by horizontal contrasts of surface wetness and size of land patches, were simulated under various background-wind conditions. Differences of temperature, specific humidity, and moist static energy as large as 4 K, 6 g/kg, and 10 kJ/kg were obtained in some cases. These differences were not affected significantly by moderate winds but were sensitive to the spatial distribution of surface wetness. These results emphasize the need to parameterize mesoscale processes induced by landscape discontinuities in GCMss.

Lynn, Barry H.↗

NASA NTRS1995

Simulations of the mesoscale circulation of the Greenland-Iceland-Norwegian Seas

The Greenland, Iceland, and Norwegian Seas provide the only link between the North Atlantic and the Arctic Oceans. This is a very dynamic region, rich in mesoscale variability. A two-layer, hydrodynamic version of the Navy layered ocean model is used to simulate the mesoscale frontal features and associated current systems. The model is wind-driven using monthly mean wind stresses and inflow/outflow mass flux from the Arctic and North Atlantic Oceans. The current transports from the model results compare favorably with transport measurements from a number of observational experiments.

Heburn, George W.↗

NASA NTRS1995

A mesoscale modeling study of the atmospheric circulation of high southern latitudes

The meteorology of high southern latitudes during winter is simulated using a cloud-free version of The Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model version 4 (MM4) with a 100-km horizontal resolution. Comparisons between idealized simulations of Antarctic with MM4 and with the mesoscale model of Parish and Waight reveal that both models produce similarly realistic velocity fields in the boundary layer. The latter model tends to produce slightly faster drainage winds over East Antarctica. The intensity of the katabatic winds produced by MM4 is sensitive to parameterizations of boundary layer fluxes. Two simulations performed with MM4 using analyses from the European Center for Medium-Range Weather Forecasts (ECMWF) for June 1988 as initial and boundary conditions. A simulation of the period from 000 UTC 2 June to 0000 UTC 8 June produces realistic synoptic phenomena including ridge development over East Antarctica, frontogenesis over the Amundsen Sea, and a katabatic surge over the Ross Ice Shelf. The simulated time-averaged fields for June 1988, particularly that of a 500-hPa height, are in good agreement with time-averaged fields analyzed by the ECMWF. The results of the simulations provide detailed features of the Antarctic winter boundary layer along the steeply sloping terrain. Highest boundary layer wind speeds averaged over the month-long simulation are approximately 20 m/s. The lack of latent heating in the simulations apparently results in some bias in the results. In particular, the cloud-free version of MM4 underpredicts the intensity of lows in the sea level pressure field.

Hines, K. M.↗

NASA NTRS1993

Magnetosheath-ionspheric plasma interactions in the cusp/cleft. 2: Mesoscale particle simulations

Ionospheric plasma flowing out from the cusp can be an important source of plasma to the magnetosphere. One source of free energy that can drive this outflow is the injection of magnetosheath plasma into the cusp. Two-dimensional (three velocity) mesoscale particle simulations are used to investigate the particle dynamics in the cusp during southward interplanetary magnetic field. This mesoscale model self-consistently incorporates (1) global influences such as the convection of plasma across the cusp, the action of the mirror force, and the injection of the magnetosheath plasma, and (2) wave-particle interactions which produce the actual coupling between the magnetosheath and ionospheric plasmas. It is shown that, because the thermal speed of the electrons is higher than the bulk motion of the magnetosheath plasma, an upward current is formed on the equatorward edge of the injection region with return currents on either side. However, the poleward return currents are the stronger due to the convection and mirroring of many of the magnetosheath electrons. The electron distribution in this latter region evolves from upward directed streams to single-sided loss cones or possibly electron conics. The ion distribution also shows a variety of distinct features that are produced by spatial and/or temporal effects associated with varying convection patterns and wave-particle interactions. On the equatorward edge the distribution has a downflowing magnetosheath component and an upflowing cold ionospheric component due to continuous convection of ionospheric plasma into the region. In the center of the magnetosheath region, heating from the development of an ion-ion streaming instability causes the suppression of the cold ionospheric component and the formation of downward ionospheric streams. Further poleward there is velocity filtering of ions with low pitch angles, so that the magnetosheath ions develop a ring-beam distribution and the ensuing wave instabilities generate downward ionospheric conics. These downward ionospheric components are eventually turned by the mirror force, leading to the production of upward conics at elevated energies throughout the region.

Winglee, R. M.↗

NASA NTRS1996

Numerical Model Studies of the Martian Mesoscale Circulations

Studies concerning mesoscale topographical effects on Martian flows examined low-level jets in the near equatorial latitudes and the dynamical intensification of flow by steep terrain. Continuation of work from previous years included evaluating the dissipation of cold air mass outbreaks due to enhanced sensible heat flux, further sensitivity and scaling evaluations for generalization of the characteristics of Martian mesoscale circulation caused by horizontal sensible heat-flux gradients, and evaluations of the significance that non-uniform surface would have on enhancing the polar CO2 ice sublimation during the spring. The sensitivity of maximum and minimum atmospheric temperatures to changes in wind speed, surface albedo, and deep soil temperature was investigated.

Segal, M.↗

NASA NTRS1994

Forecast skill of a high-resolution real-time mesoscale model designed for weather support of operations at Kennedy Space Center and Cape Canaveral Air Station

NASA funded Mesoscale Environmental Simulations and Operations (MESO), Inc. to develop a version of the Mesoscale Atmospheric Simulation System (MASS). The model has been modified specifically for short-range forecasting in the vicinity of KSC/CCAS. To accomplish this, the model domain has been limited to increase the number of horizontal grid points (and therefore grid resolution) and the model' s treatment of precipitation, radiation, and surface hydrology physics has been enhanced to predict convection forced by local variations in surface heat, moisture fluxes, and cloud shading. The objective of this paper is to (1) provide an overview of MASS including the real-time initialization and configuration for running the data pre-processor and model, and (2) to summarize the preliminary evaluation of the model's forecasts of temperature, moisture, and wind at selected rawinsonde station locations during February 1994 and July 1994. MASS is a hydrostatic, three-dimensional modeling system which includes schemes to represent planetary boundary layer processes, surface energy and moisture budgets, free atmospheric long and short wave radiation, cloud microphysics, and sub-grid scale moist convection.

Taylor, Gregory E.↗

NASA NTRS1997

Evaluating and Understanding Parameterized Convective Processes and their Role in the Development of Mesoscale Precipitation Systems

Research efforts during the second year have centered on improving the manner in which convective stabilization is achieved in the Penn State/NCAR mesoscale model MM5. Ways of improving this stabilization have been investigated by (1) refining the partitioning between the Kain-Fritsch convective parameterization scheme and the grid scale by introducing a form of moist convective adjustment; (2) using radar data to define locations of subgrid-scale convection during a dynamic initialization period; and (3) parameterizing deep-convective feedbacks as subgrid-scale sources and sinks of mass. These investigations were conducted by simulating a long-lived convectively-generated mesoscale vortex that occurred during 14-18 Jul. 1982 and the 10-11 Jun. 1985 squall line that occurred over the Kansas-Oklahoma region during the PRE-STORM experiment. The long-lived vortex tracked across the central Plains states and was responsible for multiple convective outbreaks during its lifetime.

Fritsch, J. Michael↗

NASA NTRS1997

Numerical Model Studies of the Martian Mesoscale Circulations

The study objectives were to evaluate by numerical modeling various possible mesoscale circulation on Mars and related atmospheric boundary layer processes. The study was in collaboration with J. Tillman of the University of Washington (who supported the study observationally). Interaction has been made with J. Prusa of Iowa State University in numerical modeling investigation of dynamical effects of topographically-influenced flow. Modeling simulations included evaluations of surface physical characteristics on: (i) the Martian atmospheric boundary layer and (ii) their impact on thermally and dynamically forced mesoscale flows. Special model evaluations were made in support of selection of the Pathfinder landing sites. J. Tillman's finding of VL-2 inter-annual temperature difference was followed by model simulations attempting to point out the forcing for this feature. Publication of the results in the reviewed literature in pending upon completion of the manuscripts in preparation as indicated later.

Segal, Moti↗

NASA NTRS1998

Influence of Soil Heterogeneity on Mesoscale Land Surface Fluxes During Washita '92

The influence of soil heterogeneity on the partitioning of mesoscale land surface energy fluxes at diurnal time scales is investigated over a 10(exp 6) sq km domain centered on the Little Washita Basin, Oklahoma, for the period June 10 - 18, 1992. The sensitivity study is carried out using MM5/PLACE, the Penn State/NCAR MM5 model enhanced with the Parameterization for Land-Atmosphere-Cloud Exchange or PLACE. PLACE is a one-dimensional land surface model possessing detailed plant and soil water physics algorithms, multiple soil layers, and the capacity to model subgrid heterogeneity. A series of 12-hour simulations were conducted with identical atmospheric initialization and land surface characterization but with different initial soil moisture and texture. A comparison then was made of the simulated land surface energy flux fields, the partitioning of net radiation into latent and sensible heat, and the soil moisture fields. Results indicate that heterogeneity in both soil moisture and texture affects the spatial distribution and partitioning of mesoscale energy balance. Spatial averaging results in an overprediction of latent heat flux, and an underestimation of sensible heat flux. In addition to the primary focus on the partitioning of the land surface energy, the modeling effort provided an opportunity to examine the issue of initializing the soil moisture fields for coupled three-dimensional models. For the present case, the initial soil moisture and temperature were determined from off-line modeling using PLACE at each grid box, driven with a combination of observed and assimilated data fields.

Jasinski, Michael F.↗