Michael G. Duda

A Multiscale Nonhydrostatic Atmospheric Model Using Centroidal Voronoi Tesselations and C-Grid Staggering

AbstractThe formulation of a fully compressible nonhydrostatic atmospheric model called the Model for Prediction Across Scales–Atmosphere (MPAS-A) is described. The solver is discretized using centroidal Voronoi meshes and a C-grid staggering of the prognostic variables, and it incorporates a split-explicit time-integration technique used in many existing nonhydrostatic meso- and cloud-scale models. MPAS can be applied to the globe, over limited areas of the globe, and on Cartesian planes. The Voronoi meshes are unstructured grids that permit variable horizontal resolution. These meshes allow for applications beyond uniform-resolution NWP and climate prediction, in particular allowing embedded high-resolution regions to be used for regional NWP and regional climate applications. The rationales for aspects of this formulation are discussed, and results from tests for nonhydrostatic flows on Cartesian planes and for large-scale flow on the sphere are presented. The results indicate that the solver is as acc...

Exploring a Multiresolution Modeling Approach within the Shallow-Water Equations

The ability to solve the global shallow-water equations with a conforming, variable-resolution mesh is evaluated using standard shallow-water test cases. While the long-term motivation for this study is the creation of a global climate modeling framework capable of resolving different spatial and temporal scales in differentregions,theprocessbeginswithananalysisoftheshallow-watersysteminordertobetterunderstand the strengths and weaknesses of the approach developed herein. The multiresolution meshes are spherical centroidal Voronoi tessellations where a single, user-supplied density function determines the region(s) of fine- and coarse-mesh resolution. The shallow-water system is explored with a suite of meshes ranging from quasi-uniform resolution meshes, where the grid spacing is globally uniform, to highly variable resolution meshes, where the grid spacing varies by a factor of 16 between the fine and coarse regions. The potential vorticity is found to be conserved to within machine precision and the total available energy is conserved to within a time-truncation error. This result holds for the full suite of meshes, ranging from quasi-uniform resolution and highly variable resolution meshes. Based on shallow-water test cases 2 and 5, the primary conclusion of this study is that solution error is controlled primarily by the grid resolution in the coarsest part of themodeldomain.Thisconclusionisconsistentwithresultsobtainedbyothers.Whenthesevariable-resolution meshes are used for the simulation of an unstable zonal jet, the core features of the growing instability are foundtobelargelyunchangedasthevariationinthemeshresolutionincreases.Themaindifferencesbetween the simulations occur outside the region of mesh refinement and these differences are attributed to the additional truncation error that accompanies increases in grid spacing. Overall, the results demonstrate support for this approach as a path toward multiresolution climate system modeling.

Interaction between Antarctic sea ice and synoptic activity in the circumpolar trough: implications for ice-core interpretation

Abstract Interactions between Antarctic sea ice and synoptic activity in the circumpolar trough have been investigated using meteorological data from European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-analysis and sea-ice data from passive-microwave measurements. Total Antarctic sea-ice extent does not show large interannual variations. However, large differences are observed on a regional/monthly scale, depending on prevailing winds and currents, and thus on the prevailing synoptic situations. the sea-ice edge is also a preferred region for cyclogenesis due to the strong meridional temperature gradient (high baroclinicity) in that area. the motivation for this study was to gain a better understanding of the interaction between sea-ice extent and the general atmospheric flow, particularly the frequency of warm-air intrusions into the interior of the Antarctic continent, since this influences precipitation seasonality and must be taken into account for a correct climatic interpretation of ice cores. Two case studies of extraordinary sea-ice concentration anomalies in relation to the prevailing atmospheric conditions are presented. However, both strong positive and negative anomalies can be related to warm biases in ice cores (indicated by stable-isotope ratios), especially in connection with the negative phase of the Southern Annular Mode.

Moderation of Summertime Heat Island Phenomena via Modification of the Urban Form in the Tokyo Metropolitan Area

AbstractThis study investigated the moderation of the urban heat island via changes in the urban form in the Tokyo metropolitan area (TMA). Two urban scenarios with the same population as that of the current urban form were used for sensitivity experiments: the dispersed-city and compact-city scenarios. Numerical experiments using the two urban scenarios as well as an experiment using the current urban form were conducted using a regional climate model coupled with a single-layer urban canopy model. The averaged nighttime surface air temperature in TMA increased by ~0.34°C in the dispersed-city scenario and decreased by ~0.1°C in the compact-city scenario. Therefore, the compact-city scenario had significant potential for moderating the mean areal heat-island effect in the entire TMA. Alternatively, in the central part of the TMA, these two urban-form scenarios produced opposite effects on the surface air temperature; that is, severe thermal conditions worsened further in the compact-city scenario because...

The Weather Research and Forecasting Model: Overview, System Efforts, and Future Directions

AbstractSince its initial release in 2000, the Weather Research and Forecasting (WRF) Model has become one of the world’s most widely used numerical weather prediction models. Designed to serve both research and operational needs, it has grown to offer a spectrum of options and capabilities for a wide range of applications. In addition, it underlies a number of tailored systems that address Earth system modeling beyond weather. While the WRF Model has a centralized support effort, it has become a truly community model, driven by the developments and contributions of an active worldwide user base. The WRF Model sees significant use for operational forecasting, and its research implementations are pushing the boundaries of finescale atmospheric simulation. Future model directions include developments in physics, exploiting emerging compute technologies, and ever-innovative applications. From its contributions to research, forecasting, educational, and commercial efforts worldwide, the WRF Model has made a s...

Evaluation of Global Atmospheric Solvers Using Extensions of the Jablonowski and Williamson Baroclinic Wave Test Case

AbstractThe hydrostatic and nonhydrostatic atmospheric solvers within the Model for Prediction Across Scales (MPAS) are tested using an extension of Jablonowski and Williamson baroclinic wave test case that includes moisture. This study uses the dry test case to verify the correctness of the solver formulation and coding by comparing results from the two different MPAS solvers and from the global version of the Advanced Research Weather Research and Forecasting Model (ARW-WRF). A normal mode initialization is used in the Jablonowski and Williamson test, and the most unstable mode is found to be wavenumber 9. The three solvers produce very similar normal mode structures and nonlinear baroclinic wave evolutions. Solutions produced using MPAS variable-resolution meshes are quite similar to the results from the quasi-uniform mesh with equivalent resolution. Importantly, the small-scale flow features are better resolved in the fine-resolution region and there is no apparent wave distortion in the fine-to-coars...

Strong-wind events and their influence on the formation of snow dunes: observations from Kohnen station, Dronning Maud Land, Antarctica

Analyses of shallow cores obtained at the European Project for Ice Coring in Antarctica (EPICA) drilling site Kohnen station (75800 0 S, 00804 0 E; 2892 m a.s.l.) on the plateau of Dronning Maud Land reveal the presence of conserved snow dunes in the firn. In situ observations during three dune formation events in the 2005/06 austral summer at Kohnen station show that these periods were characterized by a phase of 2 or 3 days with snowdrift prior to dune formation which only occurred during high wind speeds of >10 m s -1 at 2 m height caused by the influence of a low-pressure system. The dune surface coverage after a formation event varied between 5% and 15%, with a typical dune size of (4 � 2) m � (8 � 3) m, a maximum height of 0.2 � 0.1 m and a periodicity length of about 30 m. The mean density within a snow dune varied between 380 and 500 kg m -3 , whereas the mean density at the surrounding surface was 330 � 5k g m -3 . The firn cores covering a time-span of 22 � 2 years reveal that approximately three to eight events per year occurred, during which snow dunes had been formed and were preserved in the firn.

Analyzing the Grell–Freitas Convection Scheme from Hydrostatic to Nonhydrostatic Scales within a Global Model

AbstractThe authors implemented the Grell–Freitas (GF) parameterization of convection in which the cloud-base mass flux varies quadratically as a function of the convective updraft fraction in the global nonhydrostatic Model for Prediction Across Scales (MPAS). They evaluated the performance of GF using quasi-uniform meshes and a variable-resolution mesh centered over South America, the resolution of which varied between hydrostatic (50 km) and nonhydrostatic (3 km) scales. Four-day forecasts using a 50-km and a 15-km quasi-uniform mesh, initialized with GFS data for 0000 UTC 10 January 2014, reveal that MPAS overestimates precipitation in the tropics relative to the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis data. Results of 4-day forecasts using the variable-resolution mesh reveal that over the refined region of the mesh, GF performs as a precipitating shallow convective scheme, whereas over the coarse region of the mesh, GF acts as a conventional deep convective scheme. A...

Integrating Weather Research and Forecasting Model, Noah Land Surface Model and Urban Canopy Model for Urban Heat Island Effect Assessment

Despite increased interest on the urban heat island (UHI) phenomenon, there are limited UHI studies on cities built using the green-city concept of Sir Ebenezer Howard [1]. The administrative capital of Malaysia, Putrajaya is one of such cities built using the green-city concept. The objective of this study was to confirm the effectiveness of the green city concept using the National Centre for Atmospheric Research (NCAR) numerical technique. Numerical mesoscale Weather Research and Forecasting (WRF) Model was coupled with Noah land surface model and a single layer urban canopy model (UCM) to investigate the existence and distribution of UHI, and the behavior of urban canopy layer (2-m) temperature of Putrajaya city. Few studies have been conducted using the NCAR numerical technique (WRF) to explore Malaysian climatology. Suitability of the model employed in studying UHI phenomenon of Putrajaya city was determined using in-situ study of the area, and observational data from AlamSekitar Malaysia SdnBhd (ASMA). Contribution of urban fabrics on the spatial and temporal variations of UHI was also investigated. Comparison with ASMA and in-situ data revealed a satisfactory performance of the model.UHI intensity (UHII) of Putrajaya exhibits a diurnal profile; increasing during the night to a peak value and then diminishing towards morning with a negligible value in the mid-day. In the night time, the UHII ranges from Original Research Article

Exploring the impacts of physics and resolution on aqua-planet simulations from a nonhydrostatic global variable-resolution modeling framework

The nonhydrostatic Model for Prediction Across Scales (NH-MPAS) provides a global framework to achieve high resolution using regional mesh refinement. Previous studies using the hydrostatic version of MPAS (H-MPAS) with the physics parameterizations of Community Atmosphere Model version 4 (CAM4) found notable resolution-dependent behaviors. This study revisits the resolution sensitivity using NH-MPAS with both CAM4 and CAM5 physics. A series of aqua-planet simulations at global quasiuniform resolutions and global variable resolution with a regional mesh refinement over the tropics are analyzed, with a primary focus on the distinct characteristics of NH-MPAS in simulating precipitation, clouds, and large-scale circulation features compared to H-MPAS-CAM4. The resolution sensitivity of total precipitation and column integrated moisture in NH-MPAS is smaller than that in H-MPAS-CAM4. This contributes importantly to the reduced resolution sensitivity of large-scale circulation features such as the intertropical convergence zone and Hadley circulation in NH-MPAS compared to H-MPAS. In addition, NH-MPAS shows almost no resolution sensitivity in the simulated westerly jet, in contrast to the obvious poleward shift in H-MPAS with increasing resolution, which is partly explained by differences in the hyperdiffusion coefficients used in the two models that influence wave activity. With the reduced resolution sensitivity, simulations in the refined region of the NH-MPAS global variable resolution configuration exhibit zonally symmetric features that are more comparable to the quasiuniform high-resolution simulations than those from H-MPAS that displays zonal asymmetry in simulations inside the refined region. Overall, NH-MPAS with CAM5 physics shows less resolution sensitivity compared to CAM4.