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Moist Process Biases in Simulations of the Madden-Julian Oscillation Episodes Observed during the AMIE/DYNAMO Field Campaign

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JOURNAL OF CLIMATE 2016年第3期29卷 1091-1107页

作者： Hagos, Samson M. Feng, Zhe Burleyson, Casey D. Zhao, Chun Martini, Matus N. Berg, Larry K. Pacific NW Natl Lab 902 Battelle Blvd Richland WA 99352 USA US Navy Res Lab Monterey CA USA

Two Madden-Julian oscillation (MJO) episodes observed during the 2011 Atmospheric Radiation Measurement Program MJO Investigation Experiment (AMIE)/DYNAMO field campaign are simulated using a regional model with various cumulus parameterizations, a regional cloud-permitting model, and a global variable-resolution model with a high-resolution region centered over the tropical Indian Ocean. Model biases in relationships relevant to existing instability theories of MJO are examined and their relative contributions to the overall model errors are quantified using a linear statistical model. The model simulations capture the observed approximately log-linear relationship between moisture saturation fraction and precipitation, but precipitation associated with the given saturation fraction is overestimated especially at low saturation fraction values. This bias is a major contributor to the excessive precipitation during the suppressed phase of MJO. After accounting for this bias using a linear statistical model, the spatial and temporal structures of the model-simulated MJO episodes are much improved, and what remains of the biases is strongly correlated with biases in saturation fraction. The excess precipitation bias during the suppressed phase of the MJO episodes is accompanied by excessive column-integrated radiative forcing and surface evaporation. A large portion of the bias in evaporation is related to biases in wind speed, which are correlated with those of precipitation. These findings suggest that the precipitation bias sustains itself at least partly by cloud radiative feedbacks and convection-surface wind interactions.

关键词： Circulation Dynamics Deep convection Madden-Julian oscillation models and modeling Cloud parameterizations Cloud resolving models Convective parameterization

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Improving Parameterization of Entrainment Rate for Shallow Convection with Aircraft Measurements and Large-Eddy Simulation

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第2期73卷 761-773页

作者： Lu, Chunsong Liu, Yangang Zhang, Guang J. Wu, Xianghua Endo, Satoshi Cao, Le Li, Yueqing Guo, Xiaohao Nanjing Univ Informat Sci & Technol Collaborat Innovat Ctr Forecast & Evaluat Meteoro Key Lab Aerosol Cloud Precipitat China Meteorol Adm Nanjing Jiangsu Peoples R China Nanjing Univ Informat Sci & Technol Minist Educ Key Lab Meteorol Disaster Nanjing Jiangsu Peoples R China Chinese Acad Sci State Key Lab Numer Modeling Atmospher Sci & Geop Beijing Peoples R China Brookhaven Natl Lab Biol Environm & Climate Sci Dept Upton NY 11973 USA Univ Calif San Diego Scripps Inst Oceanog San Diego CA 92103 USA Tsinghua Univ Ctr Earth Syst Sci Beijing 100084 Peoples R China Nanjing Univ Informat Sci & Technol Sch Math & Stat Nanjing Jiangsu Peoples R China Nanjing Univ Informat Sci & Technol Key Lab Aerosol Cloud Precipitat China Meteorol A Nanjing Jiangsu Peoples R China China Meteorol Adm Inst Plateau Meteorol Chengdu Peoples R China

This work examines the relationships of entrainment rate to vertical velocity, buoyancy, and turbulent dissipation rate by applying stepwise principal component regression to observational data from shallow cumulus clouds collected during the Routine Atmospheric Radiation Measurement (ARM) Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign over the ARM Southern Great Plains (SGP) site near Lamont, Oklahoma. The cumulus clouds during the RACORO campaign simulated using a large-eddy simulation (LES) model are also examined with the same approach. The analysis shows that a combination of multiple variables can better represent entrainment rate in both the observations and LES than any single-variable fitting. Three commonly used parameterizations are also tested on the individual cloud scale. A new parameterization is thus presented that relates entrainment rate to vertical velocity, buoyancy, and dissipation rate;the effects of treating clouds as ensembles and humid shells surrounding cumulus clouds on the new parameterization are discussed. Physical mechanisms underlying the relationships of entrainment rate to vertical velocity, buoyancy, and dissipation rate are also explored.

关键词： Circulation/ Dynamics Convective clouds Atm/Ocean Structure/ Phenomena Clouds Cumulus clouds Physical Meteorology and Climatology Cumulus clouds models and modeling Cloud parameterizations Cumulus clouds

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Uncertainty in Tropical Rainfall Projections: Atmospheric Circulation Effect and the Ocean Coupling

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JOURNAL OF CLIMATE 2016年第7期29卷 2671-2687页

作者： Long, Shang-Min Xie, Shang-Ping Liu, Wei Ocean Univ China Qingdao Collaborat Innovat Ctr Marine Sci & Techn Phys Oceanog Lab Qingdao Peoples R China Ocean Univ China Ocean Atmosphere Interact & Climate Lab Qingdao Peoples R China Univ Calif San Diego Scripps Inst Oceanog 9500 Gilman DrMC 0206 La Jolla CA 92093 USA

Uncertainty in tropical rainfall projections under increasing radiative forcing is studied by using 26 models from phase 5 of the Coupled Model Intercomparison Project. Intermodel spread in projected rainfall change generally increases with interactive sea surface temperature (SST) warming in coupled models compared to atmospheric models with a common pattern of prescribed SST increase. Moisture budget analyses reveal that much of the model uncertainty in tropical rainfall projections originates from intermodel discrepancies in the dynamical contribution due to atmospheric circulation change. Intermodel singular value decomposition (SVD) analyses further show a tight coupling between the intermodel variations in SST warming pattern and circulation change in the tropics. In the zonal mean, the first SVD mode features an anomalous interhemispheric Hadley circulation, while the second mode displays an SST peak near the equator. The asymmetric mode is accompanied by a coupled pattern of wind-evaporation-SST feedback in the tropics and is further tied to interhemispheric asymmetric change in extratropical shortwave radiative flux at the top of the atmosphere. Intermodel variability in the tropical circulation change exerts a strong control on the spread in tropical cloud cover change and cloud radiative effects among models. The results indicate that understanding the coupling between the anthropogenic changes in SST pattern and atmospheric circulation holds the key to reducing uncertainties in projections of future changes in tropical rainfall and clouds.

关键词： Atm/Ocean Structure/ Phenomena Climate change Atmosphere-ocean interaction Atmospheric circulation Circulation/ Dynamics Precipitation Geographic location/entity Physical Meteorology and Climatology models and modeling Climate models Tropics

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Arbitrary-Order Conservative and Consistent Remapping and a Theory of Linear Maps: Part II

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MONTHLY WEATHER REVIEW 2016年第4期144卷 1529-1549页

作者： Ullrich, Paul A. Devendran, Dharshi Johansen, Hans Univ Calif Davis Dept Land Air & Water Resources 1 Shields Ave Davis CA 95616 USA Univ Calif Berkeley Lawrence Berkeley Natl Lab Berkeley CA 94720 USA

This paper extends on the first part of this series by describing four examples of 2D linear maps that can be constructed in accordance with the theory of the earlier work. The focus is again on spherical geometry, although these techniques can be readily extended to arbitrary manifolds. The four maps include conservative, consistent, and (optionally) monotone linear maps (i) between two finite-volume meshes, (ii) from finite-volume to finite-element meshes using a projection-type approach, (iii) from finite-volume to finite-element meshes using volumetric integration, and (iv) between two finite-element meshes. Arbitrary order of accuracy is supported for each of the described nonmonotone maps.

关键词： Interpolation schemes Interpolation schemes Numerical analysis/modeling models and modeling Mathematical and statistical techniques Data processing Algorithms Observational techniques and algorithms

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Reexamining the United Kingdom's Greatest Tornado Outbreak: Forecasting the Limited Extent of Tornadoes along a Cold Front

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WEATHER AND FORECASTING 2016年第3期31卷 853-875页

作者： Apsley, Miriam L. Mulder, Kelsey J. Schultz, David M. Univ Manchester Sch Earth Atmospher & Environm Sci Ctr Atmospher Sci Simon BldgOxford Rd Manchester M13 9PL Lancs England Univ Cambridge Christs Coll Cambridge England

On 23 November 1981, a strong cold front swept across the United Kingdom, producing tornadoes from the west to the east coasts. An extensive campaign to collect tornado reports by the Tornado and Storm Research Organisation (TORRO) resulted in 104 reports, the largest U.K. outbreak on record. The front was simulated with a convection-permitting numerical model down to 200-m horizontal grid spacing to better understand its evolution and meteorological environment. The event was typical of tornadoes in the United Kingdom, with convective available potential energy (CAPE) less than 150 J kg(-1), 0-1-km wind shear of 10-20 ms(-1), and a narrow cold-frontal rainband forming precipitation cores and gaps. A line of cyclonic absolute vorticity existed along the front, with maxima as large as 0.04 s(-1). Some hook-shaped misovortices bore kinematic similarity to supercells. The narrow swath along which the line was tornadic was bounded on the equatorward side by weak vorticity along the line and on the poleward side by zero CAPE, enclosing a region where the environment was otherwise favorable for tornadogenesis. To determine if the 104 tornado reports were plausible, first possible duplicate reports were eliminated, resulting in as few as 58 tornadoes to as many as 90. Second, the number of possible parent misovortices that may have spawned tornadoes is estimated from model output. The number of plausible tornado reports in the 200-m grid-spacing domain was 22 and as many as 44, whereas the model simulation was used to estimate 30 possible parent misovortices within this domain. These results suggest that a number of 90 reports was plausible.

关键词： Atm/Ocean Structure/ Phenomena Circulation/ Dynamics Cold fronts Forecasting Mesoscale forecasting Mesoscale models Mesoscale processes models and modeling Tornadoes Tornadogenesis

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Transient Climate Impacts for Scenarios of Aerosol Emissions from Asia: A Story of Coal versus Gas

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JOURNAL OF CLIMATE 2016年第8期29卷 2849-2867页

作者： Grandey, Benjamin S. Cheng, Haiwen Wang, Chien Singapore MIT Alliance Res & Technol Ctr Environm Sensing & Modeling Singapore Singapore MIT Ctr Global Change Sci 77 Massachusetts Ave Cambridge MA 02139 USA

Fuel usage is an important driver of anthropogenic aerosol emissions. In Asia, it is possible that aerosol emissions may increase if business continues as usual, with economic growth driving an increase in coal burning. But it is also possible that emissions may decrease rapidly as a result of the widespread adoption of cleaner technologies or a shift toward noncoal fuels, such as natural gas. In this study, the transient climate impacts of two aerosol emissions scenarios are investigated: a representative concentration pathway 4.5 (RCP4.5) control, which projects a decrease in anthropogenic aerosol emissions, and a scenario with enhanced anthropogenic aerosol emissions from Asia. A coupled atmosphere-ocean configuration of the Community Earth System Model (CESM), including the Community Atmosphere Model, version 5 (CAM5), is used. Three sets of initial conditions are used to produce a three-member ensemble for each scenario. Enhanced Asian aerosol emissions are found to exert a large cooling effect across the Northern Hemisphere, partially offsetting greenhouse gas-induced warming. Aerosol-induced suppression of the East Asian and South Asian summer monsoon precipitation occurs. The enhanced Asian aerosol emissions also remotely impact precipitation in other parts of the world. Over Australia, austral summer monsoon precipitation is enhanced, an effect associated with a southward shift of the intertropical convergence zone, driven by the aerosol-induced cooling of the Northern Hemisphere. Over the Sahel, West African monsoon precipitation is suppressed, likely via a weakening of the West African westerly jet. These results indicate that fuel usage in Asia, through the consequent aerosol emissions and associated radiative effects, might significantly influence future climate both locally and globally.

关键词： Physical Meteorology and Climatology Climate models models and modeling Aerosols Geographic location/entity Monsoons General circulation models Atm/Ocean Structure/ Phenomena Asia Climate prediction

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A Simple Shelf Circulation Model: Intrusion of Atlantic Water on the West Spitsbergen Shelf

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第4期46卷 1209-1230页

作者： Nilsen, Frank Skogseth, Ragnheid Vaardal-Lunde, Juni Inall, Mark Univ Ctr Svalbard Longyearbyen Norway Scottish Assoc Marine Sci Oban Argyll Scotland

Barotropic flow along depth contours is found in accordance with standard geostrophic theory. A numerical model is developed that studies the deviation from such a flow. The model gives a good approximation of the dynamical processes on the West Spitsbergen Shelf (WSS) and shows that the West Spitsbergen Current (WSC), the main gateway of Atlantic water (AW) toward the Arctic, connects more easily to the Isfjorden Trough than anywhere else along the shelf. The circulation of AW in the troughs along the WSS is here named the Spitsbergen Trough Current (STC). From hydrographical and ocean current observations it is evident that the STC is primarily barotropic and driven by the sea surface height. A connection between the along-coast wind stress and the STC is established, and it is demonstrated how the increased occurrence of winter cyclones in Fram Strait during January-February accelerates and widens the WSC. Ultimately, this results in a strengthened STC and dominance of AW on the WSS. The STC represents a slower route of AW toward the Arctic Ocean and a large heat transport toward the West Spitsbergen fjords during winter (0.2-0.4 TW toward Isfjorden). Heat flux estimates show that half of the AW heat loss in the Isfjorden Trough is due to heat loss to the surrounding water masses, while the rest is lost to the atmosphere. Sea ice production along West Spitsbergen has been reduced, or even nonexistent, in some fjords since 2006. Here, the authors argue that this is a consequence of the strong southerly wind periods along the WSS during winter.

关键词： Upwelling/downwelling Barotropic flows Geographic location/entity Atmosphere-ocean interaction models and modeling Circulation/ Dynamics Topographic effects Quasigeostrophic models Arctic

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Reduction of Climate Sensitivity to Solar Forcing due to Stratospheric Ozone Feedback

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JOURNAL OF CLIMATE 2016年第12期29卷 4651-4663页

作者： Chiodo, G. Polvani, L. M. Columbia Univ Dept Appl Phys & Appl Math New York NY USA Columbia Univ Dept Appl Phys & Appl Math Dept Earth & Environm Sci New York NY USA Columbia Univ Lamont Doherty Earth Observ New York NY USA

An accurate assessment of the role of solar variability is a key step toward a proper quantification of natural and anthropogenic climate change. To this end, climate models have been extensively used to quantify the solar contribution to climate variability. However, owing to the large computational cost, the bulk of modeling studies to date have been performed without interactive stratospheric photochemistry: the impact of this simplification on the modeled climate system response to solar forcing remains largely unknown. Here this impact is quantified by comparing the response of two model configurations, with and without interactive ozone chemistry. Using long integrations, robust surface temperature and precipitation responses to an idealized irradiance increase are obtained. Then, it is shown that the inclusion of interactive stratospheric chemistry significantly reduces the surface warming (by about one-third) and the accompanying precipitation response. This behavior is linked to photochemically induced stratospheric ozone changes, and their modulation of the surface solar radiation. The results herein suggest that neglecting stratospheric photochemistry leads to a sizable overestimate of the surface response to changes in solar irradiance. This has implications for simulations of the climate in the last millennium and geoengineering applications employing irradiance changes larger than those observed over the 11-yr sunspot cycle, where models often use simplified treatments of stratospheric ozone that are inconsistent with the imposed solar forcing.

关键词： Physical Meteorology and Climatology Chemistry, atmospheric Climate sensitivity Feedback models and modeling Climate models

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Comparison of the Impacts of Momentum Control Variables on High-Resolution Variational Data Assimilation and Precipitation Forecasting

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MONTHLY WEATHER REVIEW 2016年第1期144卷 149-169页

作者： Sun, Juanzhen Wang, Hongli Tong, Wenxue Zhang, Ying Lin, Chung-Yi Xu, Dongmei Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA Nanjing Univ Informat Sci & Technol Nanjing Jiangsu Peoples R China Taiwan Typhoon & Flood Res Inst Taipei Taiwan

The momentum variables of streamfunction and velocity potential are used as control variables in a number of operational variational data assimilation systems. However, in this study it is shown that, for limited-area high-resolution data assimilation, the momentum control variables and () pose potential difficulties in background error modeling and, hence, may result in degraded analysis and forecast when compared with the direct use of x and y components of wind (UV). In this study, the characteristics of the modeled background error statistics, derived from an ensemble generated from Weather Research and Forecasting (WRF) Model real-time forecasts of two summer months, are first compared between the two control variable options. Assimilation and forecast experiments are then conducted with both options for seven convective events in a domain that encompasses the Rocky Mountain Front Range using the three-dimensional variational data assimilation (3DVar) system of the WRF Model. The impacts of the two control variable options are compared in terms of their skills in short-term qualitative precipitation forecasts. Further analysis is performed for one case to examine the impacts when radar observations are included in the 3DVar assimilation. The main findings are as follows: 1) the background error modeling used in WRF 3DVar with the control variables increases the length scale and decreases the variance for u and upsilon, which causes negative impact on the analysis of the velocity field and on precipitation prediction;2) the UV-based 3DVar allows closer fits to radar wind observations;and 3) the use of UV control variables improves the 0-12-h precipitation prediction.

关键词： Forecasting Mesoscale forecasting Short-range prediction models and modeling Data assimilation Numerical analysis modeling

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The Mississippi Valley Convection Minimum on Summer Afternoons: Observations and Numerical Simulations

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MONTHLY WEATHER REVIEW 2016年第1期144卷 263-272页

作者： Kirshbaum, Daniel J. Fabry, Frederic Cazenave, Quitterie McGill Univ Dept Atmospher & Ocean Sci Montreal PQ H3A 0B9 Canada Ecole Natl Meteorol Toulouse France

Analysis of 15 years of composite radar images over the continental United States reveals a distinct minimum of deep-convection occurrence over the interior lower Mississippi Valley on summer afternoons, relative to surrounding areas. To understand the mechanisms behind this convection signature, quasi-idealized numerical simulations with the Weather Research and Forecasting (WRF) Model are performed. The simulations, which broadly reproduce the valley convection minimum, suggest that convective inhibition is maximized, and low-level ascent minimized, over the flat valley terrain. By contrast, weaker inhibition and stronger mechanically forced ascent over the hills flanking the valley combine to initiate convection more readily. Although the orography of the region is unremarkable, it has a stronger influence on the regional convection pattern than do variations in land use.

关键词： Circulation Dynamics Convective storms Orographic effects Atm Ocean Structure Phenomena Diurnal effects Physical Meteorology and Climatology Atmosphere-land interaction Observational techniques and algorithms Radars Radar observations models and modeling Mesoscale models

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