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Toward a PV-Based Algorithm for the Dynamical Core of Hydrostatic Global models

MONTHLY WEATHER REVIEW 2016年第6期144卷 2481-2502页

作者： Mohebalhojeh, Ali R. Joghataei, Mohammad Dritschel, David G. Univ Tehran Inst Geophys POB 14155-6466 Tehran *** Iran Yazd Univ Dept Phys Yazd Iran Univ St Andrews Sch Math & Stat St Andrews Fife Scotland

The diabatic contour-advective semi-Lagrangian (DCASL) algorithms previously constructed for the shallow-water and multilayer Boussinesq primitive equations are extended to multilayer non-Boussinesq equations on the sphere using a hybrid terrain-following-isentropic (sigma-) vertical coordinate. It is shown that the DCASL algorithms face challenges beyond more conventional algorithms in that various types of damping, filtering, and regularization are required for computational stability, and the nonlinearity of the hydrostatic equation in the sigma- coordinate causes convergence problems with setting up a semi-implicit time-stepping scheme to reduce computational cost. The prognostic variables are an approximation to the Rossby-Ertel potential vorticity Q, a scaled pressure thickness, the horizontal divergence, and the surface potential temperature. Results from the DCASL algorithm in two formulations of the sigma- coordinate, differing only in the rate at which the vertical coordinate tends to with increasing height, are assessed using the baroclinic instability test case introduced by Jablonowski and Williamson in 2006. The assessment is based on comparisons with available reference solutions as well as results from two other algorithms derived from the DCASL algorithm: one with a semi-Lagrangian solution for Q and another with an Eulerian grid-based solution procedure with relative vorticity replacing Q as the prognostic variable. It is shown that at intermediate resolutions, results comparable to the reference solutions can be obtained.

关键词： Mathematical and statistical techniques Isentropic analysis Numerical analysis modeling models and modeling General circulation models Numerical analysis modeling Semi-Lagrangian models Vertical coordinates

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Subtidal Exchange in Eastern Long Island Sound

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第8期46卷 2351-2371页

作者： Whitney, Michael M. Ullman, David S. Codiga, Daniel L. Univ Connecticut Dept Marine Sci 1080 Shennecossett Rd Groton CT 06340 USA Univ Rhode Isl Grad Sch Oceanog Narragansett RI 02882 USA

Long Island Sound (LIS) is a large and wide macrotidal estuary with distributed river inputs, including the Connecticut River (the largest freshwater source) that flows into the eastern LIS near the mouth. In 2010, shipboard surveys of salinity, temperature, and currents were collected along an across-estuary transect in eastern LIS. Numerical model results are compared to these observations and used to study the spatial and temporal variability of salinity, velocity, and freshwater and salt fluxes over a 4-yr period. For all low wind conditions, observations and model results indicate an outward-flowing, low-salinity wedge on the south side with an inward-flowing, higher-salinity area underneath and to the north. Observations and model results during the low wind surveys indicate that stratification substantially decreases with increased tidal amplitude and decreased river discharge;the velocity field is less variable among surveys. Model analysis indicates strong sensitivities to both tides and river discharge;with discharge response strongest for salinity and freshwater flux and tidal response larger for velocities, volume flux, and salt flux. The long-term average net freshwater and salt fluxes are outward and inward, respectively. For both flux types, subtidal shear dispersion is twice tidal oscillatory diffusion, and both contributions are in the same direction as the net flux. The uniform flow contribution is small for freshwater flux, yet it is the largest single term for salt flux and partially counters the inward contributions.

关键词： Geographic location/entity Estuaries Circulation/ Dynamics Coastal flows Transport Physical Meteorology and Climatology Salinity models and modeling Numerical analysis/modeling Regional models

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Decadal Climate Predictions Using Sequential Learning Algorithms

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JOURNAL OF CLIMATE 2016年第10期29卷 3787-3809页

作者： Strobach, Ehud Bel, Golan Ben Gurion Univ Negev Dept Solar Energy & Environm Phys Jacob Blaustein Inst Desert Res Sede Boqer Campus IL-8499000 Beer Sheva Israel

Ensembles of climate models are commonly used to improve decadal climate predictions and assess the uncertainties associated with them. Weighting the models according to their performances holds the promise of further improving their predictions. Here, an ensemble of decadal climate predictions is used to demonstrate the ability of sequential learning algorithms (SLAs) to reduce the forecast errors and reduce the uncertainties. Three different SLAs are considered, and their performances are compared with those of an equally weighted ensemble, a linear regression, and the climatology. Predictions of four different variables-the surface temperature, the zonal and meridional wind, and pressure-are considered. The spatial distributions of the performances are presented, and the statistical significance of the improvements achieved by the SLAs is tested. The reliability of the SLAs is also tested, and the advantages and limitations of the different measures of the performance are discussed. It was found that the best performances of the SLAs are achieved when the learning period is comparable to the prediction period. The spatial distribution of the SLAs performance showed that they are skillful and better than the other forecasting methods over large continuous regions. This finding suggests that, despite the fact that each of the ensemble models is not skillful, they were able to capture some physical processes that resulted in deviations from the climatology and that the SLAs enabled the extraction of this additional information.

关键词： Forecasting Climate prediction Ensembles Forecast verification/skill models and modeling Ensembles Model evaluation/performance Variability Decadal variability

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Predicting the Climatology of Tornado Occurrences in North America with a Bayesian Hierarchical modeling Framework*

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JOURNAL OF CLIMATE 2016年第5期29卷 1899-1917页

作者： Cheng, Vincent Y. S. Arhonditsis, George B. Sills, David M. L. Gough, William A. Auld, Heather Univ Toronto Dept Phys & Environm Sci Ecol Modeling Lab Toronto ON M1C 1A4 Canada Risk Sci Int Ottawa ON Canada Environm & Climate Change Canada Sci & Technol Branch Atmospher Sci & Technol Directorate Cloud Phys & Severe Weather Res Sect Toronto ON Canada Univ Toronto Dept Phys & Environm Sci Climate Lab Toronto ON M1C 1A4 Canada

Destruction and fatalities from recent tornado outbreaks in North America have raised considerable concerns regarding their climatic and geographic variability. However, regional characterization of tornado activity in relation to large-scale climatic processes remains highly uncertain. Here, a novel Bayesian hierarchical framework is developed for elucidating the spatiotemporal variability of the factors underlying tornado occurrence in North America. It is demonstrated that regional variability of tornado activity can be characterized using a hierarchical parameterization of convective available potential energy, storm relative helicity, and vertical wind shear quantities. It is shown that the spatial variability of tornado occurrence during the warm summer season can be explained by convective available potential energy and storm relative helicity alone, while vertical wind shear is clearly better at capturing the spatial variability of the cool season tornado activity. The results suggest that the Bayesian hierarchical modeling approach is effective for understanding the regional tornadic environment and in forming the basis for establishing tornado prognostic tools in North America.

关键词： Bayesian methods Mathematical and statistical techniques models and modeling Model evaluation/performance Statistical forecasting Forecasting Risk assessment Error analysis Regression analysis

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The Rapid Warming of the North Atlantic Ocean in the Mid-1990s in an Eddy-Permitting Ocean Reanalysis (1982-2013)

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JOURNAL OF CLIMATE 2016年第15期29卷 5417-5430页

作者： Yang, Chunxue Masina, Simona Bellucci, Alessio Storto, Andrea Ctr Euromediterraneo & Cambiamenti Climat Via M Franceschini 31 I-40128 Bologna Italy Ist Nazl Geofis & Vulcanol Bologna Italy

The rapid warming in the mid-1990s in the North Atlantic Ocean is investigated by means of an eddy-permitting ocean reanalysis. Both the mean state and variability, including the mid-1990s warming event, are well captured by the reanalysis. An ocean heat budget applied to the subpolar gyre (SPG) region (50 degrees-66 degrees N, 60 degrees-10 degrees W) shows that the 1995-99 rapid warming is primarily dictated by changes in the heat transport convergence term while the surface heat fluxes appear to play a minor role. The mean negative temperature increment suggests a warm bias in the model and data assimilation corrects the mean state of the model, but it is not crucial to reconstruct the time variability of the upper-ocean temperature. The decomposition of the heat transport across the southern edge of the SPG into time-mean and time-varying components shows that the SPG warming is mainly associated with both the anomalous advection of mean temperature and the mean advection of temperature anomalies across the 50 degrees N zonal section. The relative contributions of the Atlantic meridional overturning circulation (AMOC) and gyre circulation to the heat transport are also analyzed. It is shown that both the overturning and gyre components are relevant to the mid-1990s warming. In particular, the fast adjustment of the barotropic circulation response to the NAO drives the anomalous transport of mean temperature at the subtropical/subpolar boundary, while the slowly evolving AMOC feeds the large-scale advection of thermal anomalies across 50 degrees N. The persistently positive phase of the NAO during the years prior to the rapid warming likely favored the cross-gyre heat transfer and the following SPG warming.

关键词： Circulation/ Dynamics Ocean dynamics Atm/Ocean Structure/ Phenomena North Atlantic Oscillation Thermohaline circulation Physical Meteorology and Climatology Climate variability Temperature models and modeling Reanalysis data

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Urban Effects on Regional Climate: A Case Study in the Phoenix and Tucson "Sun Corridor''

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EARTH INTERACTIONS 2016年第20期20卷 1-25页

作者： Yang, Zhao Dominguez, Francina Gupta, Hoshin Zeng, Xubin Norman, Laura Univ Arizona Dept Atmospher Sci Tucson AZ USA Univ Illinois Dept Atmospher Sci 101 Atmospher Sci Bldg105 S Gregory St Urbana IL 61801 USA Univ Arizona Dept Hydrol & Water Resources Tucson AZ 85721 USA US Geol Survey Western Geog Sci Ctr Tucson AZ USA

Land-use and land-cover change (LULCC) due to urban expansion alter the surface albedo, heat capacity, and thermal conductivity of the surface. Consequently, the energy balance in urban regions is different from that of natural surfaces. To evaluate the changes in regional climate that could arise because of projected urbanization in the Phoenix-Tucson corridor, Arizona, this study applied the coupled WRF Model-Noah-Urban Canopy Model (UCM;which includes a detailed urban radiation scheme) to this region. Land-cover changes were represented using land-cover data for 2005 and projections to 2050, and historical North American Regional Reanalysis (NARR) data were used to specify the lateral boundary conditions. Results suggest that temperature changes will be well defined, reflecting the urban heat island (UHI) effect within areas experiencing LULCC. Changes in precipitation are less robust but seem to indicate reductions in precipitation over the mountainous regions northeast of Phoenix and decreased evening precipitation over the newly urbanized area.

关键词： models and modeling Coupled models Land surface model Mesoscale models Regional models

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Impact of a Stochastic Kinetic Energy Backscatter Scheme on Warm Season Convection-Allowing Ensemble Forecasts

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MONTHLY WEATHER REVIEW 2016年第5期144卷 1887-1908页

作者： Duda, Jeffrey D. Wang, Xuguang Kong, Fanyou Xue, Ming Berner, Judith Univ Oklahoma Sch Meteorol Norman OK 73072 USA Univ Oklahoma Ctr Anal & Predict Storms 120 David Boren BlvdRoom 2500 Norman OK 73072 USA Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA

The efficacy of a stochastic kinetic energy backscatter (SKEB) scheme to improve convection-allowing probabilistic forecasts was studied. While SKEB has been explored for coarse, convection-parameterizing models, studies of SKEB for convective scales are limited. Three ensembles were compared. The SKMP ensemble used mixed physics with the SKEB scheme, whereas the MP ensemble was configured identically but without using the SKEB scheme. The SK ensemble used the SKEB scheme with no physics diversity. The experiment covered May 2013 over the central United States on a 4-km Weather Research and Forecasting (WRF) Model domain. The SKEB scheme was successful in increasing the spread in all fields verified, especially mid-and upper-tropospheric fields. Additionally, the rmse of the ensemble mean was maintained or reduced, in some cases significantly. Rank histograms in the SKMP ensemble were flatter than those in the MP ensemble, indicating the SKEB scheme produces a less underdispersive forecast distribution. Some improvement was seen in probabilistic precipitation forecasts, particularly when examining Brier scores. Verification against surface observations agree with verification against Rapid Refresh (RAP) model analyses, showing that probabilistic forecasts for 2-m temperature, 2-m dewpoint, and 10-m winds were also improved using the SKEB scheme. The SK ensemble gave competitive forecasts for some fields. The SK ensemble had reduced spread compared to the MP ensemble at the surface due to the lack of physics diversity. These results suggest the potential utility of mixed physics plus the SKEB scheme in the design of convection-allowing ensemble forecasts.

关键词： Atm/Ocean Structure/ Phenomena Precipitation Thunderstorms Forecasting Forecast verification/skill Numerical weather prediction/forecasting models and modeling Ensembles Model errors

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The Vertical Structure of Tropospheric Water Vapor: Comparing Radiative and Ocean-Driven Climate Changes

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JOURNAL OF CLIMATE 2016年第11期29卷 4251-4268页

作者： Rose, Brian E. J. Rencurrel, M. Cameron SUNY Albany Dept Atmospher & Environm Sci Albany NY 12222 USA

Changes in column-integrated water vapor (Q) in response to increased CO2 and ocean heat uptake (OHU) are investigated in slab-ocean aquaplanet simulations. The simulations span a wide range of warming and moistening patterns due to the spatial structures of the imposed OHU. Fractional changes in Q per degree of surface warming range from 0% to 20% K-1 locally and from 3.6% to 11% K-1 globally. A new diagnostic technique decomposes these changes into relative humidity (RH), surface temperature, and lapse rate contributions. Single-column calculations demonstrate substantial departures from apparent (surface temperature based) Clausius-Clapeyron (CC) scaling due to lapse rates changes;a moist-adiabatic column with fixed, uniform RH exceeds the CC rate by 2.5% K-1. The RH contribution is very small in most simulations. The various Q scalings are thus all consistent CC, but result from different patterns of polar amplification and lapse rate change. Lapse rates are sensitive to location and magnitude of OHU, with implications for Q under transient climate change. CO2 with subpolar (tropical) OHU results in higher (lower) Q scalings than CO2 alone. The weakest Q scaling (and largest RH effects) is found for increased poleward ocean heat transport, which causes strongly polar-amplified warming and near-zero tropical temperature change. Despite weak RH changes and fidelity to the CC relation, Q is expected to vary widely on different time scales in nature due to sensitivity of lapse rates to OHU along with the nonlinearity of the diagnostics.

关键词： Atm/Ocean Structure/ Phenomena Climate change Climate models Heat budgets/fluxes models and modeling Physical Meteorology and Climatology Sea surface temperature Water vapor

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Large-Eddy Simulations and Damped-Oscillator models of the Unsteady Ekman Boundary Layer

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第1期73卷 25-40页

作者： Momen, Mostafa Bou-Zeid, Elie Princeton Univ Dept Civil & Environm Engn Princeton NJ 08544 USA

The Ekman boundary layer (EBL) is a central problem in geophysical fluid dynamics that emerges when the pressure gradient force, the Coriolis force, and the frictional force interact in a flow. The unsteady version of the problem, which occurs when these forces are not in equilibrium, is solvable analytically only for a limited set of forcing variability regimes, and the resulting solutions are intricate and not always easy to interpret. In this paper, large-eddy simulations (LESs) of neutral atmospheric EBLs are conducted under various unsteady forcings to reveal the range of physical characteristics of the flow. Subsequently, it is demonstrated that the dynamics of the unsteady EBL can be reduced to a second-order ordinary differential equation that is very similar to the dynamical equation of a damped oscillator, such as a mass-spring-damper system. The validation of the proposed reduced model is performed by comparing its analytical solutions to LES results, revealing very good agreement. The reduced model can be solved for a wide range of variable forcing conditions, and this feature is exploited in the paper to elucidate the physical origin of the inertia (mass), energy storage (spring), and energy dissipation (damper) attributes of Ekman flows.

关键词： Circulation Dynamics Atmospheric circulation Dynamics Ekman pumping transport Turbulence Atm Ocean Structure Phenomena Boundary layer models and modeling Large eddy simulations

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The Equatorial Energy Balance, ITCZ Position, and Double-ITCZ Bifurcations

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JOURNAL OF CLIMATE 2016年第8期29卷 2997-3013页

作者： Bischoff, Tobias Schneider, Tapio CALTECH Pasadena CA 91125 USA ETH Zurich Switzerland

The intertropical convergence zone (ITCZ) migrates north south on seasonal and longer time scales. Previous studies have shown that the zonal -mean ITCZ displacement off the equator is negatively correlated with the energy flux across the equator;when the ITCZ lies in the Northern Hemisphere, energy flows southward across the equator, and vice versa. The hemisphere that exports energy across the equator is the hemisphere with more net energy input, and it is usually the warmer hemisphere. But states with a double ITCZ straddling the equator also occur, for example, seasonally over the eastern Pacific and frequently in climate models. Here it is shown how the ITCZ position is connected to the energy balance near the equator in a broad range of circumstances, including states with single and double ITCZs. Taylor expansion of the variation of the meridional energy flux around the equator leads to the conclusion that for large positive net energy input into the equatorial atmosphere, the ITCZ position depends linearly on the cross -equatorial energy flux. For small positive equatorial net energy input, the dependence of the ITCZ position on the cross equatorial energy flux weakens to the third root. When the equatorial net energy input or its curvature become negative, a bifurcation to double-ITCZ states occurs. Simulations with an idealized aquaplanet general circulation model (GCM) confirm the quantitative adequacy of these relations. The results provide a framework for assessing and understanding causes of common climate model biases and for interpreting tropical precipitation changes, such as those evident in records of climates of the past.

关键词： Circulation/ Dynamics Atmospheric circulation Physical Meteorology and Climatology Climate change Water budget models and modeling Climate models General circulation models

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