检索结果-内蒙古大学图书馆

Objective Calibration of Regional Climate models: Application over Europe and North America

JOURNAL OF CLIMATE 2016年第2期29卷 819-838页

作者： Bellprat, Omar Kotlarski, Sven Luethi, Daniel De Elia, Ramon Frigon, Anne Laprise, Rene Schaer, Christoph Inst Catala Ciences Clima Barcelona 08005 Spain ETH Inst Atmospher & Climate Sci IAC Zurich Switzerland Consortium Climatol Reg & Adaptat Changement Clim Montreal PQ Canada Ctr Etude & Simulat Climat Echelle Reg Montreal PQ Canada

An important source of model uncertainty in climate models arises from unconfined model parameters in physical parameterizations. These parameters are commonly estimated on the basis of manual adjustments (expert tuning), which carries the risk of overtuning the parameters for a specific climate region or time period. This issue is particularly germane in the case of regional climate models (RCMs), which are often developed and used in one or a few geographical regions only. This study addresses the role of objective parameter calibration in this context. Using a previously developed objective calibration methodology, an RCM is calibrated over two regions (Europe and North America) and is used to investigate the transferability of the results. A total of eight different model parameters are calibrated, using a metamodel to account for parameter interactions. The study demonstrates that the calibration is effective in reducing model biases in both domains. For Europe, this concerns in particular a pronounced reduction of the summer warm bias and the associated overestimation of interannual temperature variability that have persisted through previous expert tuning efforts and are common in many global and regional climate models. The key process responsible for this improvement is an increased hydraulic conductivity. Higher hydraulic conductivity increases the water availability at the land surface and leads to increased evaporative cooling, stronger low cloud formation, and associated reduced incoming shortwave radiation. The calibrated parameter values are found to be almost identical for both domains;that is, the parameter calibration is transferable between the two regions. This is a promising result and indicates that models may be more universal than previously considered.

关键词： Geographic location entity Europe North America Physical Meteorology and Climatology Soil moisture Mathematical and statistical techniques Optimization models and modeling Model evaluation performance Regional models

来源：评论

学校读者我要写书评

暂无评论

Factors Controlling Stratocumulus Cloud Lifetime over Coastal Land

引用

JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第8期73卷 2961-2983页

作者： Ghonima, Mohamed S. Heus, Thijs Norris, Joel R. Kleissl, Jan Univ Calif San Diego Dept Mech & Aerosp Engn 9500 Gilman DrBldg EBU 2Room 304 La Jolla CA 92093 USA Cleveland State Univ Dept Phys 9500 Gilman DrBldg EBU 2Room 304 Cleveland OH 44115 USA Univ Calif San Diego Scripps Inst Oceanog 9500 Gilman DrBldg EBU 2Room 304 La Jolla CA 92093 USA

The breakup of stratocumulus clouds over coastal land areas is studied using a combination of large-eddy simulations (LESs) and mixed-layer models (MLMs) with a focus on mechanisms regulating the timing of the breakup. In contrast with stratocumulus over ocean, strong sensible heat flux over land prevents the cloud layer from decoupling during day. As the cloud thins during day, turbulence generated by surface flux becomes larger than turbulence generated by longwave cooling across the cloud layer. To capture this shift in turbulence generation in the MLM, an existing entrainment parameterization is extended. The MLM is able to mimic cloud evolution for a variety of Bowen ratios, but only after this modification of the entrainment parameterization. Cloud lifetime depends on a combination of the cloud-top entrainment flux, the Bowen ratio of the surface, and the strength of advection of cool ocean air by the sea breeze. For dry land surface conditions, the authors' MLM suggests a breakup time a few hours after sunrise. For relatively wet land surface conditions, the cloud layer briefly breaks into partly cloudy conditions during midday, and the stratocumulus cloud reforms in the evening.

关键词： Atm/Ocean Structure/ Phenomena Boundary layer Convective clouds Marine boundary layer Stratiform clouds Physical Meteorology and Climatology Surface fluxes models and modeling Large eddy simulations

来源：评论

学校读者我要写书评

暂无评论

A Modified Interpolation Method for Surface Total Nitrogen in the Bohai Sea

引用

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第7期33卷 1509-1517页

作者： Liu, Yongzhi Yu, Jie Shen, Youli Lv, Xianqing Ocean Univ China Phys Oceanog Lab 238 Songling Rd Qingdao 266003 Peoples R China Guangdong Ocean Univ Coll Ocean & Meteorol Guangdong Prov Key Lab Coastal Ocean Variat & Dis Guangzhou Guangdong Peoples R China State Ocean Adm Beihai Marine Environm Monitoring Ctr Stn Beihai Peoples R China

A modified Cressman interpolation method (MCIM) is presented for the routine monitoring data of total nitrogen (TN) in the Bohai Sea to reduce interpolation errors by decreasing the influence radius and introducing background value. In twin experiments, two prescribed distributions are successfully estimated by MCIM with lower interpolation errors than the traditional Cressman interpolation method (TCIM) and the kriging method. In practical experiments, cross validation is applied to evaluate the interpolation results for four quarters in 2009 and 2010. Practical experimental results show that the interpolation results obtained with MCIM are greatly improved and can describe the spatial distribution characteristics of TN in the Bohai Sea with lower mean absolute error than the kriging method.

关键词： Interpolation schemes Mathematical and statistical techniques models and modeling Numerical analysis/modeling

来源：评论

学校读者我要写书评

暂无评论

A Morphing-Based Technique for the Verification of Precipitation Forecasts

引用

MONTHLY WEATHER REVIEW 2016年第1期144卷 295-313页

作者： Han, Fan Szunyogh, Istvan Texas A&M Univ College Stn TX USA

This paper describes a morphing-based approach for the verification of precipitation forecasts. This approach employs a pyramid matching algorithm to morph the precipitation features in a forecast into features that match the related precipitation features in the verifying analysis (observations) as closely as possible. The algorithm computes an optical flow (vector field) that maps the original forecast features into the morphed forecast features. The optical flow also provides quantitative information about the error in the location of the forecast features. This information, combined with information about the error in the prediction of the total precipitation over the verification domain, is used to quantify the structure error in the precipitation forecast. The proposed approach has three novel aspects compared to the published morphing-based verification strategies. First, it imposes a constraint on the pyramid matching algorithm to prevent overconvergence toward strong precipitation features during morphing. Second, it introduces an objective criterion for the selection of the subsampling parameter to avoid splitting or distorting features due to an arbitrary maximum displacement limit. Third, the proposed definitions of the location and structure errors are new. The behavior of the proposed multivariate verification metrics is investigated by applications to both idealized and numerical forecast examples.

关键词： Forecasting Forecast verification skill models and modeling Model evaluation performance

来源：评论

学校读者我要写书评

暂无评论

Sea Spray Generation in Very High Winds

引用

JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第10期73卷 3975-3995页

作者： Ortiz-Suslow, David G. Haus, Brian K. Mehta, Sanchit Laxague, Nathan J. M. Univ Miami Rosenstiel Sch Marine & Atmospher Sci 4600 Rickenbacker Causeway Miami FL 33149 USA

Quantifying the amount and rate of sea spray production at the ocean surface is critical to understanding the effect spray has on atmospheric boundary layer processes (e.g., tropical cyclones). Currently, only limited observational data exist that can be used to validate available droplet production models. To help fill this gap, a laboratory experiment was conducted that directly observed the vertical distribution of spume droplets above actively breaking waves. The experiments were carried out in hurricane-force conditions (10-m equivalent wind speed of 36-54ms(-1)), and the observed particles ranged in radius r from 80 to nearly 1400 mm. High-resolution profiles (3 mm) were reconstructed from optical imagery taken within the boundary layer, ranging from 2 to 6 times the local significant wave height. Number concentrations were observed to have a radius dependence proportional to r(-3) leading to spume production estimates that diverge from typical source models, which tend to exhibit a radius falloff closer to r(-8). This was particularly significant for droplets with radii circa 1 mm whose modeled production rates were several orders of magnitude less than the rates expected from the observed concentrations. The vertical dependence of the number concentrations was observed to follow a logarithmic profile, which does not confirm the power-law relationship expected by a conventional spume generation parameterization. These observations bear significant implications for efforts to characterize the role these large droplets play in boundary layer processes under high-wind conditions.

关键词： Circulation/ Dynamics Small scale processes Atm/Ocean Structure/ Phenomena Boundary layer Tropical cyclones Physical Meteorology and Climatology Air-sea interaction Surface fluxes models and modeling Laboratory/physical models

来源：评论

学校读者我要写书评

暂无评论

Uncertainties in Projecting Future Changes in Atmospheric Rivers and Their Impacts on Heavy Precipitation over Europe

引用

JOURNAL OF CLIMATE 2016年第18期29卷 6711-6726页

作者： Gao, Yang Lu, Jian Leung, L. Ruby Pacific Northwest Natl Lab Atmospher Sci & Global Change Div Richland WA USA

This study investigates the North Atlantic atmospheric rivers (ARs) making landfall over western Europe in the present and future climate from the multimodel ensemble of phase 5 of the Coupled Model Intercomparison Project (CMIP5). Overall, CMIP5 captures the seasonal and spatial variations of historical landfalling AR days, with the large intermodel variability strongly correlated with the intermodel spread of historical near-surface westerly jet position. Under representative concentration pathway 8.5 (RCP8.5), AR frequency is projected to increase significantly by the end of this century, with 127%-275% increase at peak AR frequency regions (45 degrees-55 degrees N). While thermodynamics plays a dominant role in the future increase of ARs, wind changes associated with the midlatitude jet shifts also significantly contribute to AR changes, resulting in dipole change patterns in all seasons. In the North Atlantic, the model-projected jet shifts are strongly correlated with the simulated historical jet position. As models exhibit predominantly equatorward biases in the historical jet position, the large poleward jet shifts reduce AR days south of the historical mean jet position through the dynamical connections between the jet positions and AR days. Using the observed historical jet position as an emergent constraint, dynamical effects further increase future AR days over the equatorward flank above the increases from thermodynamical effects. Compared to the present, both total and extreme precipitation induced by ARs in the future contribute more to the seasonal mean and extreme precipitation, primarily because of the increase in AR frequency. While AR precipitation intensity generally increases more relative to the increase in integrated vapor transport, AR extreme precipitation intensity increases much less.

关键词： Circulation/ Dynamics Atmospheric circulation Hydrologic cycle models and modeling Climate models General circulation models

来源：评论

学校读者我要写书评

暂无评论

Aircraft Measurements and Numerical Simulations of an Expansion Fan off the California Coast

引用

JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第9期55卷 2053-2062页

作者： Parish, Thomas R. Rahn, David A. Leon, David C. Univ Wyoming Dept Atmospher Sci Laramie WY 82071 USA Univ Kansas Dept Geog & Atmospher Sci Lawrence KS 66045 USA

Mountains along the California coastline play a critical role in the dynamics of marine atmospheric boundary layer (MBL) airflow in the vicinity of the shoreline. Large changes in the MBL topology have been known to occur downwind of points and capes along the western coast of the United States. Large spatial gradients in wind and temperature become established that can cause anomalous electromagnetic wave propagation. Detailed airborne measurements using the University of Wyoming King Air were conducted to study the adjustment of the MBL to the Point Arguello and Point Conception headlands. Pronounced thinning of the MBL consistent with an expansion fan occurred to the south of Point Conception on 13 June 2012. A sharp cloud edge was collocated with the near collapse of the MBL. D-value cross sections derived from differential GPS altitude measurements allow assessment of the vertical profile of the horizontal pressure gradient force and hence thermal wind forcing in response to the near collapse of the MBL. The Weather Research and Forecasting Model was run with a 1-km grid spacing to examine the atmospheric adjustment around Point Conception during this period. Results from the simulations including the vertical cross sections of the horizontal pressure gradient force were consistent with the aircraft observations. Model results suggest that divergence occurs as the flow rounds Point Conception, characteristic of an expansion fan. Wind speeds in the MBL increase coincident with the decrease in MBL thickness, and subsiding flow associated with the near collapse of the MBL is responsible for the sharp cloud edge.

关键词： Atm/Ocean Structure/ Phenomena Marine boundary layer Observational techniques and algorithms Aircraft observations models and modeling Numerical analysis/modeling

来源：评论

学校读者我要写书评

暂无评论

Diabatic Processes and the Evolution of Two Contrasting Summer Extratropical Cyclones

引用

MONTHLY WEATHER REVIEW 2016年第9期144卷 3251-3276页

作者： Martinez-Alvarado, Oscar Gray, Suzanne L. Methven, John Univ Reading Natl Ctr Atmospher Sci Atmospher Phys Reading Berks England Univ Reading Dept Meteorol POB 243 Reading RG6 6BB Berks England

Extratropical cyclones are typically weaker and less frequent in summer as a result of differences in the background state flow and diabatic processes with respect to other seasons. Two extratropical cyclones were observed in summer 2012 with a research aircraft during the Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) field campaign. The first cyclone deepened only down to 995 hPa;the second cyclone deepened down to 978 hPa and formed a potential vorticity (PV) tower, a frequent signature of intense cyclones. The objectives of this article are to quantify the effects of diabatic processes and their parameterizations on cyclone dynamics. The cyclones were analyzed through numerical simulations incorporating tracers for the effects of diabatic processes on potential temperature and PV. The simulations were compared with radar rainfall observations and dropsonde measurements. It was found that the observed maximum vapor flux in the stronger cyclone was twice as strong as in the weaker cyclone;the water vapor mass flow along the warm conveyor belt of the stronger cyclone was over half that typical in winter. The model overestimated water vapor mass flow by approximately a factor of 2 as a result of deeper structure in the rearward flow and humidity in the weaker case. An integral tracer interpretation is introduced, relating the tracers with cross-isentropic mass transport and circulation. It is shown that the circulation around the cyclone increases much more slowly than the amplitude of the diabatically generated PV tower. This effect is explained using the PV impermeability theorem.

关键词： Circulation/ Dynamics Extratropical cyclones Large-scale motions Mesoscale processes Subgrid-scale processes Mathematical and statistical techniques Isentropic analysis models and modeling Tracers

来源：评论

学校读者我要写书评

暂无评论

Oceanic Turbulent Energy Budget using Large-Eddy Simulation of a Wind Event during DYNAMO

引用

JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第3期46卷 827-840页

作者： Hoecker-Martinez, Martin S. Smyth, William D. Skyllingstad, Eric D. Oregon State Univ 104 CEOAS Adm Bldg Corvallis OR 97331 USA

The dominant processes governing ocean mixing during an active phase of the Madden-Julian oscillation are identified. Air-sea fluxes and upper-ocean currents and hydrography, measured aboard the R/V Revelle during boreal fall 2011 in the Indian Ocean at 0 degrees, 80.5 degrees E, are integrated by means of a large-eddy simulation (LES) to infer mixing mechanisms and quantify the resulting vertical property fluxes. In the simulation, wind accelerates the mixed layer, and shear mixes the momentum downward, causing the mixed layer base to descend. Turbulent kinetic energy gains due to shear production and Langmuir circulations are opposed by stirring gravity and frictional losses. The strongest stirring of buoyancy follows precipitation events and penetrates to the base of the mixed layer. The focus here is on the initial 24 h of an unusually strong wind burst that began on 24 November 2011. The model shows that Langmuir turbulence influences only the uppermost few meters of the ocean. Below the wave-energized region, shear instability responds to the integrated momentum flux into the mixed layer, lagging the initial onset of the storm. Shear below the mixed layer persists after the storm has weakened and decelerates the surface jet slowly (compared with the acceleration at the peak of the storm). Slow loss of momentum from the mixed layer extends the effect of the surface wind burst by energizing the fluid at the base of the mixed layer, thereby prolonging heat uptake due to the storm. Ocean turbulence and air-sea fluxes contribute to the cooling of the mixed layer approximately in the ratio 1:3, consistent with observations.

关键词： models and modeling Mixed layer Large eddy simulations Geographic location/entity Mixing Physical Meteorology and Climatology Fluxes Indian Ocean Atm/Ocean Structure/Phenomena Tropics

来源：评论

学校读者我要写书评

暂无评论

Investigating the Eddy Diffusivity Concept in the Coastal Ocean

引用

JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第7期46卷 2201-2218页

作者： Rypina, I. I. Kirincich, A. Lentz, S. Sundermeyer, M. Woods Hole Oceanog Inst Woods Hole MA 02543 USA Univ Massachusetts Dartmouth New Bedford MA USA

This paper aims to test the validity, utility, and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a high-resolution (800 m) high-frequency radar south of Martha's Vineyard, Massachusetts. Specifically, this study investigates how well a combination of radar-based velocities and drifter-derived diffusivities can reproduce observed dye spreading over an 8-h time interval. Adrifter-based estimate of an anisotropic diffusivity tensor is used to parameterize small-scale motions that are unresolved and underresolved by the radar system. This leads to a significant improvement in the ability of the radar to reproduce the observed dye spreading.

关键词： Circulation/ Dynamics Coastal flows Diffusion Lagrangian circulation/transport Observational techniques and algorithms Radars/Radar observations models and modeling Tracers

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：