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Impact of Parameterized Physical Processes on Simulated Tropical Cyclone Characteristics in the Community Atmosphere Model

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JOURNAL OF CLIMATE 2015年第24期28卷 9857-9872页

作者： He, Fei Posselt, Derek J. Univ Michigan Dept Climate & Space Sci & Engn Ann Arbor MI 48109 USA

This study advances the understanding of how parameterized physical processes affect the development of tropical cyclones (TCs) in the Community Atmosphere Model (CAM) using the Reed-Jablonowski TC test case. It examines the impact of changes in 24 parameters across multiple physical parameterization schemes that represent convection, turbulence, precipitation, and cloud processes. The one-at-a-time (OAT) sensitivity analysis method quantifies the relative influence of each parameter on TC simulations and identifies which parameters affect six different TC characteristics: intensity, precipitation, longwave cloud radiative forcing (LWCF), shortwave cloud radiative forcing (SWCF), cloud liquid water path (LWP), and ice water path (IWP). It is shown that TC intensity is mainly sensitive to the parcel fractional mass entrainment rate (dmpdz) in deep convection. A decrease in this parameter can lead to a change in simulated intensity from a tropical depression to a category-4 storm. Precipitation and SWCF are strongly affected by three parameters in deep convection: tau (time scale for consumption rate of convective available potential energy), dmpdz, and C0_ocn (precipitation coefficient). Changes in physical parameters generally do not affect LWCF much. In contrast, LWP and IWP are very sensitive to changes in C0_ocn. The changes can be as large as 10 (5) times the control mean value for LWP (IWP). Further examination of the response functions for the subset of most sensitive parameters reveals nonlinear relationships between parameters and most output variables, suggesting that linear perturbation analysis may produce misleading results when applied to strongly nonlinear systems.

关键词： Atm Ocean Structure Phenomena Tropical cyclones observational techniques and algorithms Sensitivity studies Models and modeling General circulation models Parameterization Subgrid-scale processes

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A Z_DR Column Detection Algorithm to Examine Convective Storm Updrafts

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WEATHER AND FORECASTING 2015年第6期30卷 1819-1844页

作者： Snyder, Jeffrey C. Ryzhkov, Alexander V. Kumjian, Matthew R. Khain, Alexander P. Picca, Joseph Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA NOAA Natl Severe Storms Lab OAR Norman OK 73069 USA Penn State Univ Dept Meteorol University Pk PA 16802 USA Hebrew Univ Jerusalem Dept Atmospher Sci Jerusalem Israel NOAA NWS NCEP Storm Predict Ctr Norman OK USA

Observations and recent high-resolution numerical model simulations indicate that liquid water and partially frozen hydrometeors can be lofted considerably above the environmental 0 degrees C level in the updrafts of convective storms owing to the warm thermal perturbation from latent heating within the updraft and to the noninstantaneous nature of drop freezing. Consequently, upward extensions of positive differential reflectivity (i.e., Z(DR) >= 1 dB)-called Z(DR) columns-may be a useful proxy for detecting the initiation of new convective storms and examining the evolution of convective storm updrafts. High-resolution numerical simulations with spectral bin microphysics and a polarimetric forward operator reveal a strong spatial association between updrafts and Z(DR) columns and show the utility of examining the structure and evolution of Z(DR) columns for assessing updraft evolution. This paper introduces an automated Z(DR) column algorithm designed to provide additional diagnostic and prognostic information pertinent to convective storm nowcasting. Although suboptimal vertical resolution above the 0 degrees C level and limitations imposed by commonly used scanning strategies in the operational WSR-88D network can complicate Z(DR) column detection, examples provided herein show that the algorithm can provide operational and research-focused meteorologists with valuable information about the evolution of convective storms.

关键词： Atm/Ocean Structure/ Phenomena Severe storms Physical Meteorology and Climatology Cloud microphysics Convective storms observational techniques and algorithms algorithms Radars/Radar observations Forecasting Nowcasting

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The Relationship between Automated Low-Level Velocity Calculations from the WSR-88D and Maximum Tornado Intensity Determined from Damage Surveys

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WEATHER AND FORECASTING 2015年第5期30卷 1125-1139页

作者： Kingfield, Darrel M. LaDue, James G. Univ Oklahoma Norman OK 73019 USA NOAA OAR Natl Severe Storms Lab Norman OK USA Natl Weather Serv Warning Decis Training Div Norman OK USA

The relationship between automated low-level velocity derived from WSR-88D severe storm algorithms and two groups of tornado intensity were evaluated using a 4-yr climatology of 1975 tornado events spawned from 1655 supercells and 320 quasi-linear convective systems (QLCSs). A comparison of peak velocity from groups of detections from the Mesocyclone Detection Algorithm and Tornado Detection Algorithm for each tornado track found overlapping distributions when discriminating between weak [rated as category 0 or 1 on the enhanced Fujita scale (EF0 and EF1)] and strong (EF2-5) events for both rotational and delta velocities. Dataset thresholding by estimated affected population lowered the range of observed velocities, particularly for weak tornadoes while retaining a greater frequency of events for strong tornadoes. Heidke skill scores for strength discrimination were dependent on algorithm, velocity parameter, population threshold, and convective mode, and varied from 0.23 and 0.66. Bootstrapping the skill scores for each algorithm showed a wide range of low-level velocities (at least 7 m s(-1) in width) providing an equivalent optimal skill at discriminating between weak and strong tornadoes. This ultimately limits identification of a single threshold for optimal strength discrimination but the results match closely with larger prior manual studies of low-level velocities.

关键词： Atm Ocean Structure Phenomena Tornadoes observational techniques and algorithms algorithms Radars Radar observations Forecasting Operational forecasting Applications Damage assessment

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Characteristics and Synoptic Environment of Drylines Occurring over the Higher Terrain of Southeastern Wyoming

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WEATHER AND FORECASTING 2015年第6期30卷 1733-1748页

作者： Bergmaier, Philip T. Geerts, Bart Univ Wyoming Dept Atmospher Sci Laramie WY 82071 USA

Commonly observed over the broadly sloped terrain of the southern Great Plains (SGP), drylines are frequent loci of warm season deep convection and have been the focus of numerous observational, theoretical, and climatological studies over last half century. In this study, a 3-yr (2010-12) analysis of the characteristics and synoptic environment of drylines occurring elsewhere, over the high terrain in southeastern Wyoming just east of the Rocky Mountains, is presented. Observed on similar to 11% of the days between May and August of the years examined, southeastern Wyoming drylines were often associated with large moisture gradients [similar to 5-10 g kg(-1) (100 km)(-1)], large horizontal virtual potential temperature differences (similar to 2-5 K), and convergent zonal wind flow at the surface. The synoptic conditions leading to their formation and their relationship to thunderstorm activity are also explored in an effort to aid local forecasters in anticipating the development and convective impact of drylines across the region. Similarities exist between these drylines and those found over the SGP, especially with regard to their strength and close relationship to deep convection. However, the frequency at which they occur, some characteristics of their diurnal motion, and the synoptic conditions driving their formation differ noticeably.

关键词： Atm/Ocean Structure/ Phenomena Drylines Physical Meteorology and Climatology Climatology observational techniques and algorithms Radars/Radar observations Surface observations Forecasting Operational forecasting

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Low-Frequency Seiche in a Large Bay

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第3期45卷 716-723页

作者： MacMahan, Jamie Naval Postgrad Sch Dept Oceanog 833 Dyer RdBldg 232Room 327c Monterey CA 93943 USA

Short-term observations of sea surface elevations eta along the 10-m isobath and long-term observations inside and outside of a large bay (Monterey Bay, CA) were obtained to describe the nodal structure of the modes 0-3 seiches within the bay and the low-frequency (<346 cpd) seiche forcing mechanism. The measured nodal pattern validates previous numerical estimates associated with a northern amplitude bias, though variability exists across the modal frequency band, particularly for modes 0 and 1. Low-frequency oceanic eta white noise within seiche frequency bands (24-69 cpd) provides a continuous resonant forcing of the bay seiche with a eta(2) (variance) amplification of 16-40 for the different modes. The temporal variation of the oceanic eta white noise is significantly correlated (R-2 = 0.86) at the 95% confidence interval with the bay seiche eta that varies seasonally. The oceanic eta white noise is hypothesized as being from low-frequency, free, infragravity waves that are forced by short waves.

关键词： Circulation/ Dynamics Wave properties Waves oceanic observational techniques and algorithms In situ oceanic observations

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A New Paradigm for the North Pacific Subthermocline Low-Latitude Western Boundary Current System

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第9期45卷 2407-2423页

作者： Qiu, Bo Chen, Shuiming Rudnick, Daniel L. Kashino, Yuji Univ Hawaii Manoa Dept Oceanog Honolulu HI 96822 USA Univ Calif San Diego Scripps Inst Oceanog La Jolla CA 92093 USA Japan Agcy Marine Earth Sci & Technol Ctr Earth Informat Sci & Technol Yokohama Kanagawa Japan

Subthermocline western boundary circulation along the low-latitude North Pacific Ocean (2 degrees-25 degrees N) is investigated by using profiling float and historical CTD/expendable CTD (XCTD) data and by analyzing an eddy-resolving global OGCM output. In contrast to the existing paradigm depicting it as a reversed pattern of the wind-driven circulation above the ventilated thermocline (i.e., depth < 26.8 sigma(theta)), the subthermocline western boundary circulation is found to comprise two components governed by distinct dynamical processes. For meridional scales shorter than 400 km, the boundary flows along the Philippine coast exhibit convergent patterns near 7 degrees, 10 degrees, 13 degrees, and 18 degrees N, respectively. These short-scale boundary flows are driven by the subthermocline eastward zonal jets that exist coherently across the interior North Pacific basin and are generated by the triad instability of wind-forced annual baroclinic Rossby waves. For meridional scales longer than 400 km, a time-mean Mindanao Undercurrent (MUC) is observed from 6 degrees to 13 degrees N together with another northward-flowing boundary flow beneath the Kuroshio from 16 degrees to 24 degrees N. Rather than remote eddy forcing from the interior Pacific Ocean, both of these broad-scale subthermocline boundary flows are induced by baroclinic instability of the overlying wind-driven western boundary currents, the Mindanao Current, and Kuroshio.

关键词： Geographic location/entity North Pacific Ocean Circulation/ Dynamics Boundary currents Eddies Ocean circulation observational techniques and algorithms In situ oceanic observations Models and modeling General circulation models

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The Evolution of the Goddard Profiling Algorithm to a Fully Parametric Scheme

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2015年第12期32卷 2265-2280页

作者： Kummerow, Christian D. Randel, David L. Kulie, Mark Wang, Nai-Yu Ferraro, Ralph Munchak, S. Joseph Petkovic, Veljko Colorado State Univ Dept Atmospher Sci Ft Collins CO 80523 USA Univ Wisconsin Madison WI USA IM Syst Grp College Pk MD USA NOAA NESDIS College Pk MD USA Univ Maryland Earth Syst Sci Interdisciplinary Ctr College Pk MD 20742 USA

The Goddard profiling algorithm has evolved from a pseudoparametric algorithm used in the current TRMM operational product (GPROF 2010) to a fully parametric approach used operationally in the GPM era (GPROF 2014). The fully parametric approach uses a Bayesian inversion for all surface types. The algorithm thus abandons rainfall screening procedures and instead uses the full brightness temperature vector to obtain the most likely precipitation state. This paper offers a complete description of the GPROF 2010 and GPROF 2014 algorithms and assesses the sensitivity of the algorithm to assumptions related to channel uncertainty as well as ancillary data. Uncertainties in precipitation are generally less than 1%-2% for realistic assumptions in channel uncertainties. Consistency among different radiometers is extremely good over oceans. Consistency over land is also good if the diurnal cycle is accounted for by sampling GMI product only at the time of day that different sensors operate. While accounting for only a modest amount of the total precipitation, snow-covered surfaces exhibit differences of up to 25% between sensors traceable to the availability of high-frequency (166 and 183 GHz) channels. In general, comparisons against early versions of GPM's Ku-band radar precipitation estimates are fairly consistent but absolute differences will be more carefully evaluated once GPROF 2014 is upgraded to use the full GPM-combined radar-radiometer product for its a priori database. The combined algorithm represents a physically constructed database that is consistent with both the GPM radars and the GMI observations, and thus it is the ideal basis for a Bayesian approach that can be extended to an arbitrary passive microwave sensor.

关键词： Atm/Ocean Structure/Phenomena Precipitation observational techniques and algorithms algorithms Microwave observations Satellite observations

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The Signature of Aerosols and Meteorology in Long-Term Cloud Radar Observations of Trade Wind Cumuli

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2015年第12期72卷 4643-4659页

作者： Lonitz, Katrin Stevens, Bjorn Nuijens, Louise Sant, Vivek Hirsch, Lutz Seifert, Axel Max Planck Inst Meteorol D-20146 Hamburg Germany European Ctr Medium Range Weather Forecasts Reading RG2 9AX Berks England Deutsch Wetterdienst Hans Ertel Ctr Weather Res Hamburg Germany

The signature of aerosols and meteorology on the development of precipitation from shallow cumuli in the trades is investigated with ground-based lidar and radar remote sensing. The measurements are taken from a cloud observatory recently established on the windward shore of Barbados. Cloud microphysical development is explored through an analysis of the radar echo of shallow cumuli before the development of active precipitation. The increase of reflectivity with height (Z gradient) depends on the amount of cloud water, which varies with meteorology, and cloud droplet number concentration N, which varies with the aerosol. Clouds with a large Z gradient have a higher tendency to form precipitation than clouds with a small Z gradient. Under similar meteorological conditions, the Z gradient is expected to be large in an environment with few aerosols and small in an environment with many aerosols. The aerosol environment is defined using three methods, but only one (based on the Raman lidar linear-depolarization ratio) to measure dusty conditions correlates significantly with the Z gradient. On average, nondusty days are characterized by a larger Z gradient. However, the dust concentration varies seasonally and covaries with relative humidity. Large-eddy simulations show that small changes in the relative humidity can have as much influence on the development of precipitation within the cloud layer as large changes in N. When clouds are conditioned on their ambient relative humidity, the sensitivity of the Z gradient to dust vanishes.

关键词： Atm Ocean Structure Phenomena Clouds Convective clouds Cumulus clouds Precipitation Physical Meteorology and Climatology Aerosols observational techniques and algorithms Radars Radar observations

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Cloud Regime Variability over the Azores and Its Application to Climate Model Evaluation

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JOURNAL OF CLIMATE 2015年第24期28卷 9707-9720页

作者： Remillard, Jasmine Tselioudis, George Columbia Univ New York NY USA NASA Goddard Inst Space Studies New York NY 10025 USA

From its location on the subtropics-midlatitude boundary, the Azores is influenced by both the subtropical high pressure and the midlatitude baroclinic storm regimes and therefore experiences a wide range of cloud structures, from fair-weather scenes to stratocumulus sheets and deep convective systems. This work combines three types of datasets to study cloud variability in the Azores: a satellite analysis of cloud regimes, a reanalysis characterization of storminess, and a 19-month field campaign that occurred on Graciosa Island. Combined analysis of the three datasets provides a detailed picture of cloud variability and the respective dynamic influences, with emphasis on low clouds that constitute a major uncertainty source in climate model simulations. The satellite cloud regime analysis shows that the Azores cloud distribution is similar to the mean global distribution and can therefore be used to evaluate cloud simulation in global models. Regime analysis of low clouds shows that stratocumulus decks occur under the influence of the Azores high pressure system, while shallow cumulus clouds are sustained by cold-air outbreaks, as revealed by their preference for postfrontal environments and northwesterly flows. An evaluation of climate model cloud regimes from phase 5 of CMIP (CMIP5) over the Azores shows that all models severely underpredict shallow cumulus clouds, while most models also underpredict the occurrence of stratocumulus cloud decks. It is demonstrated that the regime analysis can assist in the selection of case studies representing specific climatological cloud distributions. With all the tools now in place, a methodology is suggested to better understand cloud-dynamics interactions and attempt to explain and correct climate model cloud deficiencies.

关键词： Atm Ocean Structure Phenomena Cumulus clouds Stratiform clouds Physical Meteorology and Climatology Clouds observational techniques and algorithms Climate classification regimes Models and modeling Climate models

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A Wake due to the Maldives in the Eastward Wyrtki Jet

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2015年第7期45卷 1858-1876页

作者： Nagura, Motoki Masumoto, Yukio Japan Agcy Marine Earth Sci & Technol Res & Dev Ctr Global Change Yokosuka Kanagawa 2370061 Japan Univ Tokyo Grad Sch Sci Tokyo 113 Japan

A wake due to islands in background zonal flow has been observed in the equatorial Pacific Ocean. This study detects and examines a wake due to the Maldives in the eastward Wyrtki jet in the Indian Ocean. Observations by acoustic Doppler current profilers deployed east of the Maldives show semiannual variability in cross-equatorial currents, which cannot be explained by annual monsoonal wind forcing. Output from a high-resolution ocean general circulation model (OGCM) shows that the semiannual current variability is a part of a stationary wavelike pattern of meridional currents, which appears east of the Maldives concurrently with the eastward Wyrtki jet. Idealized numerical experiments are conducted using a 1.5-layer model, in which an equatorial jet driven by wind forcing or steady inflow impinges islands that are similar to the Maldives in shape. The results show the meandering of the equatorial eastward jet east of the model islands, and the resulting cross-equatorial currents have a similar pattern compared to those in the OGCM simulation. The momentum budget analysis obtained from the OGCM simulation and the layer model experiments shows a significant contribution of momentum advection to the generation of the wake. Also, the layer model experiments exhibit that the wake is essentially stationary;its zonal wavelength becomes larger when the eastward jet is stronger, and the wake is absent when the equatorial jet is westward. The similarity of the wake in the equatorial jet to stationary damped Rossby waves in the quasigeostrophic barotropic ocean model is discussed.

关键词： Geographic location entity Indian Ocean Circulation Dynamics Topographic effects observational techniques and algorithms In situ oceanic observations Models and modeling Ocean models Variability Seasonal variability

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