Table of Contents  Director's Message  Executive Summary  MMM Achievements 

MMM Achievements 

Multiscale Convective Cloud Systems and WavesThe systemic properties of moist convection are fundamental to weather and climate and, in particular, to the Earth’s water and energy cycles. Multiscale numerical simulation and mathematical models provide a pathway to improved parameterization. Figure 56 shows the crossdisciplinary approach adopted in the multiscale investigations reported in this section, which range from observed systems in need of explanation, numerical simulation, superparameterization and mathematical reductionism, to improved parameterization. History shows that the latter is resistent to solution and thus a major challenge.
The research themes reported below center on atmospheric convection, its interaction with the boundary layer and ocean/land interfaces, and wave dynamics. Since no geophysical model can simulate convection from first principles (cloudmicrophysics and radiative transfer must be parameterized), improved parameterization of microphysics is needed. Because the multiscale cloudsystem models (grid interval ~1 km) resolve mesoscale circulations, the largescale role of organized convection with its strong dynamical effects, is high on the research agenda. The multipurpose numerical model framework known as EULAG developed by Piotr Smolarkiewicz and collaborators is the mainstay of the multiscale simulation approach. When a dataassimilating model is required (i.e., realworld case studies), MM5 is used. EULAG developmentEULAG is a numerical code for simulating geophysical flows on all scales – a facility for numerical experimentation in a virtual laboratory with timedependent adaptive meshes and complex, even timedependent, computational domains. The underlying anelastic equations are solved in either a EULerian (flux form) or a LAGrangian (advective form) framework. EULAGs generality derives from a unique model design that combines the nonoscillatory forwardintime (NFT) numerical algorithms (based on the MPDATA family of transport schemes) and a robust elliptic solver in generalized coordinates. The numerical code contains options for controlling numerical accuracy and allows a wide range of numerical sensitivity tests. The model equations are formulated with various options. For example, in addition to simulation of the Earth’s atmosphere, options are available for stellar atmospheres, ocean dynamics, sanddune propagation and biomechanical flows. The EULAG code is fully parallelized and easily portable between computer platforms. Previous model development and details of the numerical algorithms are published in peerreviewed papers by P. Smolarkiewicz and colleagues. Developments of EULAG during FY2004 are now summarized. Dynamic Grid Deformation
Joseph Prusa (Iowa State University) and P. Smolarkiewicz continued the development of a deformablecoordinate option designed using synergetic interaction between rules of continuous mapping and the strengths of the NFT methods. Previously, they demonstrated that effective multiscale adaptive numerical models for high Reynolds number geophysical flows can dispense with rigorous evaluation of more cumbersome vector differential operators, such as the curl of the velocity and the strain rate. Nevertheless, these operators are important for budget analyses of the model results, estimating physical uncertainties, driving the mesh adaptivity, and extending applicability beyond standard meteorological situations. Recently they documented extensions of the generic explicitly inviscid approach for curvilinear representation of the vorticity, Fickian diffusion, strain, and stress as well as tensor identities complement the entire development. The benefits of their approach are substantial. The narrower and more complex the geometry of the problem, the more prohibitive the cost of standard simulations on rectangular domains. For example, for a valley flow in the following figure, the gain is about a factor of two. Spectral PreconditionersThomas et al. (MWR, 2003) reported advantages of elementary constantcoefficient spectral preconditioners for elliptic problems in atmospheric flows, in the context of the Canadian MC2 model (a semiLagrangian, semiimplicit, elastic, nonhydrostatic, multiscale research/weatherprediction model). A followup study by P. Smolarkiewicz, Steven Thomas (SCD), Clive Temperton (ECMWF), and Andrzej Wyszogrodzki (LANL) incorporated spectral preconditioners in EULAG. They tested performance of spectral preconditioners in extreme settings covering a broad range of scales and physical applications: from canonical decaying turbulence in a triply periodic box, through homogeneous flows past largeamplitude undulating boundaries, mesoscale flows past long winding valleys, to idealized climate. Their results do not corroborate the universal superiority of spectral preconditioners (over simple linerelaxation schemes) found in MC2. While elementary spectral preconditioners offer substantial advantages in many applications; in general, their performance is unsatisfactory when significant horizontal inhomogeneity occurs. UnstructuredGrids
Testing a numerical approach in a parameter space distinct from its normal application is enlightening. Joanna Szmelter (Cranfield University, UK) and Piotr Smolarkiewicz (MMM) continued development of MPDATA in an arbitrary finitevolume framework with a fully unstructured polyhedral hybrid mesh. They advanced the stability theory, included the monotonicity enhancement and generalized the approach to a fully compressible flow solver. The new framework is well suited to adapting the Cartesian mesh experience with MPDATA in an unstructured grid environment. Their results reported for the transonic flow around airfoils are promising from the perspective that the method is substantially less diffusive than contemporary computations normally used in aeronautical design. Their studies of flow past 2D airfoils are the first documented application of an MPDATAbased flow solver in multiconnected domains. The ease of modeling multiconnected domains using unstructured meshes opens new avenues for MPDATA for atmospheric/oceanic flows, for which the scheme was developed originally. Dynamical analoguesThe objective here is to reduce complex multiscale dynamical systems to simple forms, which is a necessary step toward the understanding that can help parameterization of the systemic effects, especially dynamically based aspects such as momentum transport. Progress toward achieving this objective is summarized below. QuasiBiennial Oscillation (QBO)The QBO represents the dominant variability in the equatorial lower stratosphere, yet complete understanding has remained elusive despite numerous studies. Nils Wedi (ECMWF) and P. Smolarkiewicz continued their basic research of the QBO. Using EULAG, they conducted a direct numerical simulation of the celebrated laboratory experiment of Plumb and McEwan (1978) and its KyotoUniversity counterpartoften employed to demonstrate basic properties of the QBO reproducing the laboratory results. A series of 2D and 3D numerical simulations exhibits a number of internal gravity wave processes: wave reflection, wavewavemean flow interaction, criticallayer formation and subsequent wave breaking. All have atmospheric counterparts. A comprehensive analysis led to the conclusion that spatial background flow perturbations due to internal wavewave interactions and subsequent momentum flux changes enhanced by wave breaking, grow locally to critical magnitude and merge to form a downward propagating mean shear layer. Furthermore, in contrast to the original explanation the next phase of the laboratory oscillation is a result of the reversed background wind forcing acting against the oscillating membrane.
MaddenJulian Oscillation (MJO)
Mitch Moncrieff completed a study of nonlinear MJO dynamics. By formulating a dynamical model he showed the pivotal role of the mesoscale organization of convection on the largescale coherence of tropical convection. The general model formulation consists of two interlocked systems: a mesoscale parameterization of organized convection and a twolayer model of largescale equatorial dynamics. The lowerlayer dynamics is Rossby gyre–like, whereas outflow from organized convection maintains the upperlayer circulation. The transports of zonal momentum in the vertical and meridional directions are key processes. An archetype of the general model (Figure 61), in spite of being brutally simplified, represents the convective organization, momentum transport, and equatorial superrotation realized by the cloud resolving convection parameterization (CRCP) approach developed by Wojciech Grabowski. The mesoscale parameterization is an analytic equivalent of the cloudsystemresolving models used in the CRCP approach. Finally, issues in the parameterization of convective organization were quantified. Diurnal cycle of convection and effects of orographyThe relationship among organized convection, orography (local and remote effects), largescale flow and the diurnal cycle is inadequately represented in largescale models that apply convective parameterization. For this reason, simulations that resolve convection, or at least its mesoscale organization, are compared to simulations that apply convective parameterization. Organized Traveling Precipitation over the U.S. Continent
This work is collaborative with the Water Cycle Across Scales initiative, which is now part of The Institute for Multidisciplinary Earth Studies (TIMES). Changhai Liu and M. Moncrieff continued their multiscale simulation of warmseason convection over the U.S. continent using explicit and parameterized approaches  a set of 7day simulations (from 3 to 10 July 2003) using MM5 with 3km, 10km, and 30km grid resolution and model domain 2400km x 1800km. MM5 is initialized with the 3hourly 40km ETA model analysis. This period is characterized by moderate synoptic forcing, in contrast to relatively benign largescale conditions in the 10day period (20 to 30 July 1998) reported in FY2003. Remarkably, both the explicit and parameterized simulations reproduce the observed daily convective regeneration over the Rockies and subsequent eastward propagation (Figure 62a). Diagnostic analyses show that coldpool dynamics and interaction between latent heating and the ambient flow are responsible for the simulated coherent precipitation. The propagation speed is explained by a nonlinear theoreticaldynamical model of convection in shear. Figure 62b compares Budget analysis indicate that the coarsegrid simulations underestimate the lowertropospheric cooling and uppertropospheric warming and overestimate the convective drying at most levels. Temporal Variability of Precipitation over the U.S. Continent
Hsiaoming Hsu (RAP), Wenwen Tung (ASP), C. Liu and M. Moncrieff analyzed directionally averaged time series of rain rates derived from NEXRAD measurements over the continental U. S. by Carbone et al (2002). Using spectral decomposition methods they found distinct classes of temporal variability. Latitudinallyaveraged time series indicated a remarkable selfsimilarity for the frequency band higher than semidiurnal, quantified by a powerlaw scaling with an exponent of 4/3 (Figure 63). For the longitudinally averaged series, the scaling exponent for the frequency band higher than semidiurnal changes from 4/3 to 5/3. The difference between the latitudinal and longitudinal spectra is interpreted as a consequence of the anisotropy of the patterns of highfrequency precipitation. The scaleinvariance is useful for evaluating the statistics of precipitation in finescale prediction models and cloudresolving models. Composites of the higherfrequency bands display eastward propagation of the reconstructed convective patterns, whereas the lowfrequency patterns propagate westward. There is a marked interannual variability in the dominant periods and the propagation speeds. Diurnal Variability over the Bay of BengalSatellite observations by Yang and Slingo, (2001) show that propagating deep convection over the Bay of Bengal during the summer monsoon originates over the mountainous region of eastern India, in broad agreement with observations over the Bay obtained during the JASMINE Pilot Study (Webster et al. 2002). C. Liu, M. Moncrieff and John Tuttle have started an observational analysis of organized convection and diurnal variability over the Bay of Bengal. TRMM rainfall data, zonally averaged from 82.5E to 92.5E for three warm seasons (MaySeptember 2002, 2003 and 2004), show frequent propagating convection during active phases of the monsoon. Convection initiates over the Eastern Ghats in the afternoon or evening and subsequently travels hundreds of kilometers towards the equator. Documentation of the statistical properties of propagation speed, longitudinal scale, and morphology of the rainfall streaks is underway. This is intended to be a basis for idealized numerical simulation and theoreticaldynamical modeling of diurnal variability and convective organization. Diurnal Variability over the Tibetan PlateauXiaodong Liu (Institute of Earth Environment, Chinese Academy of Sciences, China) and C. Liu have started investigations of the warmseason diurnal variations of convective activities over the Tibetan Plateau and adjacent regions. This research is intended to document the mean diurnal variabilities of rainfall, radiative fluxes, and clouds and to quantify the performance of modern mesoscale numerical models in capturing the observed diurnal variations. In the observational analysis, the TRMM rainfall data, the Japanese GMS IR data, and the ERBE data are used to examine the diurnal variations of precipitation, cloudiness, and outgoing longwave radiation, respectively. In the numerical modeling, a regional climate model is employed to conduct a set of threeyear simulations. Resolved Orographic Forcing in a Global Model
J. Prusa and P. Smolarkiewicz examined the effects of grid refinement in the vicinity of the Andes Mountains, in the context of HeldSuarez climate simulations. The complex geometry and narrow eastwest extent of the Andes is a challenge for numerical models. To address this problem, the adaptive gridrefinement approach in EULAG was utilized in global simulations to locally enhance resolution in the vicinity of an idealized topography. Their results show that insufficient local resolution strongly impacts global behavior. The conditions under which regional errors produce significant global errors depend on the terrain elevation and local climate. At midsouthern latitudes, their model gives reasonable global climate statistics even with resolution so coarse that the mountains are approximated (longitudinally) by a Delta function. However, for the weaker zonal flow in the equatorial region, insufficient resolution spuriously generates a westerly jet near the equatorial tropopause, making it necessary to fully resolve significant orography. About an order of magnitude gain is achieved by the adaptive grid compared to a uniform highresolution grid. Figure 64 shows the global effect of orography. Multiscale convective organization in the TropicsUnderstanding the multiscale behavior of convection over the tropical oceans is largely a problem in convectiveradiativedynamical quasiequilibrium, which is addressed by multiscale numerical models in large domains, global models operating superparameterization and regional prediction models. LargeScale Organization in the Indian Summer Monsoon RegionWenwen Tung (ASP), M. Moncrieff and Hsiaoming Hsu (RAP) have started a regional modeling study of the meso to largescale convective organization in the Indian summer monsoon region. They are running MM5 with three interactively nested domains. ECMWF TOGA analysis provides largescale background and lateral boundary conditions. The simulation in the largest domain is nudged toward the analysis using the FDDA technique. The subsequent domains with finer resolution are judiciously placed to further resolve the convective events in the Bay of Bengal. Their objective is to understand the multiscale organization of convection and its predictability in the Bay, with the emphasis on the physical processes controlling diurnal to severalday convective variability. The results are compared against TRMM satelliteobserved rainfall during Auguest 2003. Numerous tests are being done on the effectiveness of cumulus parameterization and microphysical schemes. Preliminary results suggest that, under the current FDDA and nesting framework, the combination of the BettsMiller cumulus parameterization and the GSFC microphysical schemes produces convective organizations with realistic phase and orientation over the Bay. Vertical Evolution of ConvectionTetsuya Takemi (Osaka University, Japan) and C. Liu completed investigations of the relationship between the vertical development of tropical cumulus convection and the vertical profiles of environmental temperature and moisture. The analyses of observational data obtained in the tropical western Pacific region reveal a strong correlation between the development of shallow and middletopped cumulus clouds and the existence of dry layers in the middle to upper troposphere. In contrast, the difference in static stability profiles is insignificant among cloud regimes. The observed importance of the tropospheric moisture in modulating cumulus modes is supported by cloudresolving numerical simulations, which show a strong sensitivity of cumulus heights to the mid to upperlevel relative humidity, while the midlevel stable layer has less impact. Variability over the Tropical PacificWenwen Tung (ASP), M. Moncrieff and JianBos Gao (University of Florida) completed a study of multiscale convective variability over the Pacific Ocean using a highresolution index (ITBB) derived from satellite imagery. They found that convective activity with lifetimes ranging from about 1 h to 21 days have a crossscale interdependence described by power laws. The ITBB displays longrange dependency, meaning that intense convection tends to be followed by another intense event, and vice versa for weakened events or droughts. This tendency is stronger with larger domain averaging due to largerscale variability such as superclusters associated with the MJO. The evolution of cloud clusters within an MJO event showed that convective activity along the front, center, and rear parts of the event continuously intensify approaching the date line and indicate multifractal features in the range of 1 h to about 5–10 days. Convective activity along the front and rear edges of the MJO event are more intermittent than in the center. The multifractal features of the ITBB time series were approximated by a random multiplicative cascade process, suggesting multiscale behavior and sobering for the predictability of observed phenomena. NCARNCMRWF Collaborative ResearchNCAR and the National Centre for Medium Range Weather Forecasting (NCMRWF), New Delhi, India have a memorandum of understanding addressing three objectives:
Convective parameterizationFrom the start of numerical weather prediction over half a century ago and the start of modern climate modeling in the early 1990’s, the parameterization of convection and the radiative properties of convectively generated clouds has been the root of major uncertainty. Reducing uncertainty is a problem having many facets. Our approach is to use cloudsystemresolving models, evaluation of singlecolumn models, with focus on the diurnal cycle and organization of deep convection. Much effort has been put into improving convective parameterization using finescale models, and is now a worldwide effort involving international programs. Daytime Convective Development over Land
The GEWEX (Global Energy and Water Cycle Experiment) Cloud System Study (GCSS), which is an international coordinating body consisting of five working groups, has existed since the early 1990s. For two years, ending January 2004, the working group on Precipitating Convective Cloud Systems was chaired by W. Grabowski. He fostered collaborative work on daytime convective development over land in singlecolumn models (SCMs) and cloudresolving models (CRMs). The scientists involved are Peter Bechtold (ECMWF), Anning Cheng and KuanMan Xu (both NASALangley), Richard Forbes, Carol Halliwell, Jon Petch, and Ricky Wong (all from UK Met Office), Marat Khairoutdinov (Colorado State University), Steve Lang and WeiKuo Tao (NASA Goddard), Tomoe Nasuno (Japan Agency for MarineEarth Science and Technology), and Xiaoqing Wu (Iowa State University). They developed an idealized model intercomparison based on observations of the diurnal cycle during the rainy season in Amazonia. The focus was a 6hr period between sunrise and early afternoon, previously identified as being critical for the diurnal cycle over summertime continents. This period is characterized by the formation and growth of a wellmixed convective boundary layer, proceeding to shallow convective clouds as the convective boundary layer deepens,and subsequent transition to precipitating convection around local noon. A benchmark customdesigned set of simulations was devised. The SCMs reproduced previouslyidentified problems with premature development of deep convection, less than two hours after sunrise. CRMs with ~1 km horizontal gridresolution capture the benchmark simulations qualitatively, but with significant differences among the models. Twodimensional CRMs tend to simulate too rapid a transition from shallow to deep convection and toohigh a cloud cover. CloudResolving Convection Parameterization in the CAM
Michal Ziemianski (visiting postdoctoral fellow from the Institute of Meteorology and Water Management, Poland), in collaboration with W. Grabowski, M. Moncrieff, and William Collins (CGD) completed an investigation of convective organization over the tropical western Pacific warm pool using the cloudresolving convection parameterization (CRCP, or superparameterization) and the Community Atmospheric Model (CAM) of the Community Climate System Model (CCSM). The CRCP simulations show significant improvements of the warm pool climate. The cloud condensate distribution is much improved as well as the bias of the tropopause height. More realistic structure of the intertropical convergence zone (ITCZ) during the boreal winter and better representation of the variability of convection are evident. In particular, the diurnal cycle of precipitation has phase and amplitude in good agreement with observations. Also improved is the largescale organization of the tropical convection involving superclusters associated with MaddenJulian Oscillation (MJO)like systems. Location and propagation characteristics, as well as lower tropospheric cyclonic and uppertropospheric anticyclonic gyres are more realistic than in the standard CAM. The simulations support an analytic theory of dynamical coupling between organized convection and equatorial betaplane dynamics. Evaluation of Cumulus ParameterizationJames Hack, Julie Caron (both CGD), C. Liu, and M. Moncrieff have started the evaluation of the convective parameterization scheme in CCSM through cloudresolving and singlecolumn model (SCM) modeling. They are particularly interested in the capability of the cumulus parameterization in reproducing the observed phase of the diurnal cycle of US middlesummer convection. In their threestep approach, multiday cloudresolving simulations are conducted with a mesoscale model. Then, the advective tendencies for temperature and moisture averaged over a selective area are derived and are used to drive an SCM as "largescale" forcing. Finally, the performance of the convective parameterization is evaluated through comparing the SCM results against cloudresolving model results and observations. They are currently focusing on two 300km x 300km regions, which are characteristic of afternoonevening maximum convection over the Continental Divide and nocturnal maximum rainfall over the Great Plains, respectively. The cloudresolving simulations have been completed, and the SCM simulations are still under way.
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Table of Contents  Director's
Message  Executive
Summary  MMM
Achievements 