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A Mathematical Framework for Analysis of Water Tracers. Part II: Understanding Large-Scale Perturbations in the Hydrological Cycle due to CO₂ Doubling

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JOURNAL OF CLIMATE 2016年第18期29卷 6765-6782页

作者： Singh, Hansi K. A. Bitz, Cecilia M. Donohoe, Aaron Nusbaumer, Jesse Noone, David C. Univ Washington Dept Atmospher Sci Box 351640 Seattle WA 98195 USA Univ Washington Appl Phys Lab Seattle WA 98105 USA Univ Colorado Dept Atmospher & Ocean Sci Boulder CO 80309 USA Univ Colorado Cooperat Inst Res Environm Sci Boulder CO 80309 USA Oregon State Univ Dept Earth Ocean & Atmospher Sci Corvallis OR 97331 USA

The aerial hydrological cycle response to CO2 doubling from a Lagrangian, rather than Eulerian, perspective is evaluated using information from numerical water tracers implemented in a global climate model. While increased surface evaporation (both local and remote) increases precipitation globally, changes in transport are necessary to create a spatial pattern where precipitation decreases in the subtropics and increases substantially at the equator. Overall, changes in the convergence of remotely evaporated moisture are more important to the overall precipitation change than changes in the amount of locally evaporated moisture that precipitates in situ. It is found that CO2 doubling increases the fraction of locally evaporated moisture that is exported, enhances moisture exchange between ocean basins, and shifts moisture convergence within a given basin toward greater distances between moisture source (evaporation) and sink (precipitation) regions. These changes can be understood in terms of the increased residence time of water in the atmosphere with CO2 doubling, which corresponds to an increase in the advective length scale of moisture transport. As a result, the distance between where moisture evaporates and where it precipitates increases. Analyses of several heuristic models further support this finding.

关键词： Circulation/ Dynamics Hydrologic cycle Lagrangian circulation/transport Atm/Ocean Structure/ Phenomena Precipitation Physical Meteorology and Climatology Climate change Moisture/moisture budget models and modeling Tracers

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Efficient Kernel-Based Ensemble Gaussian Mixture Filtering

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MONTHLY WEATHER REVIEW 2016年第2期144卷 781-800页

作者： Liu, Bo Ait-El-Fquih, Boujemaa Hoteit, Ibrahim King Abdullah Univ Sci & Technol Thuwal Saudi Arabia

The Bayesian filtering problem for data assimilation is considered following the kernel-based ensemble Gaussian mixture filtering (EnGMF) approach introduced by Anderson and Anderson. In this approach, the posterior distribution of the system state is propagated with the model using the ensemble Monte Carlo method, providing a forecast ensemble that is then used to construct a prior Gaussian mixture (GM) based on the kernel density estimator. This results in two update steps: a Kalman filter (KF)-like update of the ensemble members and a particle filter (PF)-like update of the weights, followed by a resampling step to start a new forecast cycle. After formulating EnGMF for any observational operator, the influence of the bandwidth parameter of the kernel function on the covariance of the posterior distribution is analyzed. Then the focus is on two aspects: (i) the efficient implementation of EnGMF with (relatively) small ensembles, where a new deterministic resampling strategy is proposed preserving the first two moments of the posterior GM to limit the sampling error;and (ii) the analysis of the effect of the bandwidth parameter on contributions of KF and PF updates and on the weights variance. Numerical results using the Lorenz-96 model are presented to assess the behavior of EnGMF with deterministic resampling, study its sensitivity to different parameters and settings, and evaluate its performance against ensemble KFs. The proposed EnGMF approach with deterministic resampling suggests improved estimates in all tested scenarios, and is shown to require less localization and to be less sensitive to the choice of filtering parameters.

关键词： Forecasting Ensembles Forecasting techniques Probability forecasts models distribution models and modeling Data assimilation

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A Comparison of Two Ensemble Generation Methods Using Oceanic Singular Vectors and Atmospheric Lagged Initialization for Decadal Climate Prediction

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MONTHLY WEATHER REVIEW 2016年第7期144卷 2719-2738页

作者： Marini, Camille Polkova, Iuliia Koehl, Armin Stammer, Detlef Univ Hamburg Ctr Erdsyst Forsch & Nachhaltigkeit Inst Meereskunde Hamburg Germany

The sensitivity of ensemble spread and forecast skill scores of decadal predictions to details of the ensemble generation is investigated by incorporating uncertainties of ocean initial conditions using ocean singular-vector-based (OSV) perturbations. Results are compared to a traditional atmospheric lagged initialization (ALI) method. Both sets of experiments are performed using the coupled MPI-ESM model initialized from the GECCO2 ocean synthesis. The OSVs are calculated from a linear inverse model based on a historical MPI-ESM run. During the first three lead years, the sea surface temperature spread from ALI hindcasts appears to be strongly underestimated, while OSV hindcasts show a more realistic spread. However, for later lead times (the second pentad of hindcasts), the spread becomes overestimated for large areas of the ocean in both ensembles. Yet, for integrated measures such as the North Atlantic SST and Atlantic meridional overturning circulation, the spread of OSV hindcasts is overestimated at initial time and reduces over time. The spread reliability measures are shown to be sensitive to the choice of the verification dataset. In this context, it is found that HadISST tends to underestimate the variability of SST as compared to Reynolds SST and satellite observations. In terms of forecast skill for surface air temperature, SST, and ocean heat content, OSV hindcasts show improvement over ALI hindcasts over the North Atlantic Ocean up to lead year 5.

关键词： Climate prediction Ensembles Forecast verification/skill Forecasting Interannual variability Mathematical and statistical techniques Model initialization models and modeling Singular vectors Variability

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On the Equilibrium-State Roll Vortices and Their Effects in the Hurricane Boundary Layer

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第3期73卷 1205-1222页

作者： Gao, Kun Ginis, Isaac Univ Rhode Isl Grad Sch Oceanog 215 South Ferry Rd Narragansett RI 02882 USA

In this study, the authors numerically simulate roll vortices (rolls) generated by the inflection-point instability in the hurricane boundary layer (HBL). The approach is based on embedding a two-dimensional high-resolution single-grid roll-resolving model (SRM) at selected horizontal grid points of an axisymmetric HBL model. The results from a set of idealized experiments indicate that the mixed-layer height is an important factor affecting the magnitude of the roll velocities and the structure of the internal waves triggered in the stably stratified layer above. This study reveals the important difference between the roll-induced cross-roll (nearly radial) and along-roll (nearly azimuthal) momentum fluxes: while the cross-roll momentum flux is well correlated to the cross-roll mean wind shear, the along-roll momentum flux is typically not correlated with the along-roll mean wind shear. Therefore, the commonly used K theory in the boundary layer parameterizations cannot reasonably capture the vertical distribution of the roll-induced along-roll momentum flux. Moreover, the authors find that the rolls induce more significant changes in the mean radial wind profile than in the mean azimuthal wind profile. Specifically, rolls reduce the inflow near surface, enhance the inflow at upper levels, and increase the inflow-layer height. Based on a linear dynamical HBL model, the authors find that the impact of rolls on the mean radial wind profile is essentially due to their redistribution effect on the mean azimuthal momentum in the HBL.

关键词： Numerical analysis/modeling Hurricanes/typhoons Subgrid-scale processes Boundary layer models and modeling Atm/Ocean Structure/ Phenomena

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Projecting and Forecasting Winter Precipitation Extremes and Meteorological Drought in California Using the North Pacific High Sea Level Pressure Anomaly

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JOURNAL OF CLIMATE 2016年第13期29卷 5009-5026页

作者： Costa-Cabral, Mariza Rath, John S. Mills, William B. Roy, Sujoy B. Bromirski, Peter D. Milesi, Cristina Northwest Hydraul Consultants Inc 16300 Christensen RdSuite 350 Seattle WA 98188 USA Tetra Tech Inc Res & Dev Grp Lafayette CA USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA NASA Ames Res Ctr Moffett Field CA 94035 USA

Large-scale climatic indices have been used as predictors of precipitation totals and extremes in many studies and are used operationally in weather forecasts to circumvent the difficulty in obtaining robust dynamical simulations of precipitation. The authors show that the sea level pressure North Pacific high (NPH) wintertime anomaly, a component of the Northern Oscillation index (NOI), provides a superior covariate of interannual precipitation variability in Northern California, including seasonal precipitation totals, drought, and extreme precipitation intensity, compared to traditional ENSO indices such as the Southern Oscillation index (SOI), the multivariate ENSO index (MEI), NiNo-3.4, and others. Furthermore, the authors show that the NPH anomaly more closely reflects the influence of Pacific basin conditions over California in general, over groups of stations used to characterize statewide precipitation in the Sierra Nevada range, and over the southern San Francisco Bay region (NASA Ames Research Center). This paper uses the term prediction to refer to the estimation of precipitation (the predictand) from a climate covariate (the predictor), such as a climate index, or atmospheric moisture. In this sense, predictor and predictand are simultaneous in time. Statistical models employed show the effectiveness of the NPH winter anomaly as a predictor of total winter precipitation and daily precipitation extremes at the Moffett Field station. NPH projected by global climate models is also used in conjunction with atmospheric humidity [atmospheric specific humidity (HUS) at the 850-hPa level] to obtain projections of mean and extreme precipitation. The authors show that future development of accurate forecasts of NPH anomalies issued several months in advance is important for forecasting total winter precipitation and is expected to directly benefit water resource management in California. Therefore, the authors suggest that investigating the lead-time predictabili

关键词： Circulation/ Dynamics ENSO Walker circulation Mathematical and statistical techniques Bayesian methods Forecasting Statistical forecasting models and modeling General circulation models Reanalysis data

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Impact of Assimilating Surface Velocity Observations on the Model Sea Surface Height Using the NCOM-4DVAR*

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MONTHLY WEATHER REVIEW 2016年第3期144卷 1051-1068页

作者： Carrier, Matthew J. Ngodock, Hans E. Muscarella, Philip Smith, Scott Naval Res Lab Bldg 1009 Balch Blvd Stennis Space Ctr MS 39529 USA

The assimilation of surface velocity observations and their impact on the model sea surface height (SSH) is examined using an operational regional ocean model and its four-dimensional variational data assimilation (4DVAR) analysis component. In this work, drifter-derived surface velocity observations are assimilated into the Navy's Coastal Ocean Model (NCOM) 4DVAR in weak-constraint mode for a Gulf of Mexico (GoM) experiment during August-September 2012. During this period the model is trained by assimilating surface velocity observations (in a series of 96-h assimilation windows), which is followed by a 30-day forecast through the month of October 2012. A free-run model and a model that assimilates along-track SSH observations are also run as baseline experiments to which the other experiments are compared. It is shown here that the assimilation of surface velocity measurements has a substantial impact on improving the model representation of the forecast SSH on par with the experiment that assimilates along-track SSH observations directly. Finally, an assimilation experiment is done where both along-track SSH and velocity observations are utilized in an attempt to determine if the observation types are redundant or complementary. It is found that the combination of observations provides the best SSH forecast, in terms of the fit to observations, when compared to the previous experiments.

关键词： Ocean models Model initialization Forecasting Data assimilation models and modeling Forecasting Variational analysis Mathematical and statistical techniques

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Prediction and Ensemble Forecast Verification of Hail in the Supercell Storms of 20 May 2013

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WEATHER AND FORECASTING 2016年第3期31卷 811-825页

作者： Snook, Nathan Jung, Youngsun Brotzge, Jerald Putnam, Bryan Xue, Ming Ctr Anal & Predict Storms Norman OK USA New York State Mesonet Albany NY USA SUNY Albany Albany NY 12222 USA Univ Oklahoma Ctr Anal & Predict Storms Rm 5425120 David Boren Blvd Norman OK 73072 USA Univ Oklahoma Sch Meteorol Norman OK 73019 USA

Despite recent advances in storm-scale ensemble NWP, short-term(0-90 min) explicit forecasts of severe hail remain a major challenge as a result of the fast evolution and short time scales of hail-producing convective storms and the substantial uncertainty associated with the microphysical representation of hail. In this study, 0-90-min ensemble hail forecasts for the supercell storms of 20 May 2013 over central Oklahoma are examined and verified, with the goals of 1) evaluating ensemble forecast performance, 2) comparing the advantages and limitations of different forecast fields potentially suitable for the prediction of hail and severe hail in a Warn-on-Forecast setting, and 3) evaluating the use of dual-polarization radar observations for hail forecast validation. To address the challenges of hail prediction and to produce skillful forecasts, the ensemble uses a two-moment microphysics scheme that explicitly predicts a hail-like rimed-ice category and is run with a grid spacing of 500 m. Radar reflectivity factor and radial velocity, along with surface observations, are assimilated every 5 min for 1 h as the storms were developing to maturity, followed by a 90-min ensemble forecast. Several methods of hail prediction and hail forecast verification are then examined, including the prediction of the maximum hail size compared to Storm Prediction Center (SPC) and Meteorological Phenomena Identification Near the Ground (mPING) hail observations, and verification of model data against single-and dual-polarization radar-derived fields including hydrometeor classification algorithm (HCA) output and the maximum estimated size of hail (MESH). The 0-90-min ensemble hail predictions are found to be marginally to moderately skillful depending on the verification method used.

关键词： Storm forecasting Finite element method Hail Radar Mathematical models Polarization Dual polarization radar Property damage Storms Fields Ice Reflectance Studies Classification Uncertainty Algorithms Radar reflectivity Kalman filters Hydrometeors Weather forecasting Evolution Size Velocity Convective storms Microphysics Forecast verification Program verification (computers) Ground-based observation Information sources Rain Radial velocity Atm/Ocean Structure/ Phenomena Hail Supercells Forecasting Ensembles Forecast verification/skill models and modeling Numerical weather prediction/forecasting

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Climatology of Wind, Kinetic Energy, and Temperature Spectra Using a High-Resolution Climate Model for Mid-Europe

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JOURNAL OF CLIMATE 2016年第3期29卷 963-974页

作者： Zentek, Rolf Heinemann, Guenther Sachs, Ekkehard Univ Trier Dept Environm Meteorol Behringstr 21 D-54286 Trier Germany Univ Trier Dept Math Trier Germany

Spectra of wind, kinetic energy, and temperature are investigated for a dataset of 10 years of regional climate simulations for mid-Europe. The nonhydrostatic Consortium for Small-Scale modeling (COSMO) model in Climate Mode [COSMO-CLM (CCLM)] climate model is used in a hindcast mode for 1991-2000. The threestep nesting chain starts with a CCLM run with 18-km resolution covering all of Europe nested in ERA-40 reanalyses and then a run with a resolution of 4.4km is performed for mid-Europe. Finally, the 1.3-km run focuses on the region of mid-Germany and Luxembourg. In the present study, only results for the 4.4-and 1.3-km runs are shown. Different methods based on the Fourier and cosine transformations for the computation of the spectra are evaluated. The kinetic energy spectra showthe expected -5/3 slope in the mesoscale (up to the effective resolution), while the spectrum of the vertical wind shows a zero-slope behavior. The spectra of the horizontal wind components and temperature compare well to the observations. The effective model resolution was found to be about 7-10 (5-7) times the horizontal grid spacing for the one-dimensional (two-dimensional) spectral methods. A comparison between the differentmodel resolutions shows a benefit of the 1.3-km simulations for the boundary layer for horizontal scales up to 25 km. The multiyear time-scale simulations allow for a climatological study of the seasonal cycle. The kinetic energy spectrum is found to have the largest values in summer.

关键词： Mathematical and statistical techniques Fourier analysis models and modeling Climate models Model output statistics Numerical analysis modeling Spectral analysis models distribution Variability Seasonal variability

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Expansion of a Holepunch Cloud by a Gravity Wave Front

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第2期73卷 693-707页

作者： Muraki, David J. Rotunno, Richard Morrison, Hugh Simon Fraser Univ Dept Math 8888 Univ Dr Burnaby BC V5A 1S6 Canada Natl Ctr Atmospher Res Boulder CO USA

A holepunch cloud is a curious phenomenon where a disturbance in a thin cloud layer initiates an expanding circular hole of clear air. Usually triggered by the passage of aircraft, observations of these holes in clouds date back to the earliest days of aviation, but only recently has a holepunch cloud been simulated within a full-physics numerical model. These computations confirm that ice crystal growth through the Wegener-Bergeron-Findeisen process creates a small cloud-free region whose subsequent outward spread defines the holepunch. The mechanics behind this continued expansion, however, has yet to be definitively identified. In this article, the motion of the cloud edge is explained as a propagating gravity wave front. To support this idea, a hierarchy of three idealizations is analyzed: a full-physics numerical model, a fluid mechanical model with simplified moisture effects, and a conservation law analysis for front motion. The essence of the holepunch cloud is established to be a moist air layer that is unsaturated (clear) and weakly stratified within the hole but saturated (cloudy) and moist neutral outside of it. The cloud edge thus represents a barrier to the outward propagation of gravity waves within the clear air-the result of this collision is a wave front whose velocity determines the growth rate of the hole.

关键词： Circulation/ Dynamics Gravity waves Atm/Ocean Structure/ Phenomena Clouds Physical Meteorology and Climatology Cloud microphysics models and modeling Clouds

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The Precipitation Response to an Idealized Subtropical Continent

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JOURNAL OF CLIMATE 2016年第12期29卷 4543-4564页

作者： Maroon, Elizabeth A. Frierson, Dargan M. W. Kang, Sarah M. Scheff, Jacob Univ Washington Dept Atmospher Sci Box 351640 Seattle WA 98115 USA Ulsan Natl Inst Sci & Technol Sch Urban & Environm Engn Ulsan South Korea Columbia Univ Lamont Doherty Earth Observ Palisades NY USA

A subtropical continent is added to two aquaplanet atmospheric general circulation models (AGCMs) to better understand the influence of land on tropical circulation and precipitation. The first model, the gray-radiation moist (GRaM) AGCM, has simplified physics, while the second model, the GFDL Atmospheric Model version 2.1 (AM2.1), is a fully comprehensive AGCM. Both models have a continent that is 608 wide in longitude from 10 degrees to 30 degrees N, in an otherwise slab-ocean-covered world. The precipitation response varies with cloudy-and clear-sky feedbacks and depends on continental albedo. In GRaM simulations with a continent, precipitation in the Northern Hemisphere decreases mostly as a result of decreased evaporation. In AM2.1 simulations, precipitation also shifts southward via Hadley circulation changes due to increasing albedo, but the radiative impact of clouds and moisture creates a more complex response. Results are similar when a seasonal cycle of insolation is included in AM2.1 simulations. The impact of a large, bright subtropical continent is to shift precipitation to the opposite hemisphere. In these simulations, the hemisphere of greater tropical precipitation is better predicted by the hemisphere with greater atmospheric energy input, as has been shown in previous literature, rather than the hemisphere that has higher surface temperature.

关键词： Geographic location/entity Intertropical convergence zone Circulation/ Dynamics Energy transport Hadley circulation Atm/Ocean Structure/ Phenomena Monsoons Precipitation models and modeling General circulation models

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