scholarly journals On the Definition of Precipitation Efficiency

2007 ◽  
Vol 64 (12) ◽  
pp. 4506-4513 ◽  
Author(s):  
Chung-Hsiung Sui ◽  
Xiaofan Li ◽  
Ming-Jen Yang
Keyword(s):  
Large Scale ◽  
Spatial Scales ◽  
Cloud Microphysics ◽  
Tropical Ocean ◽  
Precipitation Efficiency ◽  
Surface Rainfall ◽  
Time Period ◽  
Toga Coare ◽  
Highly Correlated ◽  
Definition Of

Abstract A modified definition of precipitation efficiency (PE) is proposed based on either cloud microphysics precipitation efficiency (CMPE) or water cycling processes including water vapor and hydrometeor species [large-scale precipitation efficiency (LSPE)]. These PEs are examined based on a two-dimensional cloud-resolving simulation. The model is integrated for 21 days with the imposed large-scale vertical velocity, zonal wind, and horizontal advections obtained from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). It is found that the properly defined PEs include all moisture and hydrometeor sources associated with surface rainfall processes so that they range from 0% to 100%. Furthermore, the modified LSPE and CMPE are highly correlated. Their linear correlation coefficient and root-mean-squared difference are insensitive to the spatial scales of averaged data and are moderately sensitive to the time period of averaged data.

scholarly journals Estimation of Oceanic Precipitation Efficiency in Cloud Models

2005 ◽  
Vol 62 (12) ◽  
pp. 4358-4370 ◽  
Author(s):  
Chung-Hsiung Sui ◽  
Xiaofan Li ◽  
Ming-Jen Yang ◽  
Hsiao-Ling Huang
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Cloud Microphysics ◽  
Convective System ◽  
Source Surface ◽  
Tropical Ocean ◽  
Precipitation Efficiency ◽  
Cloud Models ◽  
Toga Coare ◽  
Hourly Data

Abstract Precipitation efficiency is estimated based on vertically integrated budgets of water vapor and clouds using hourly data from both two-dimensional (2D) and three-dimensional (3D) cloud-resolving simulations. The 2D cloud-resolving model is forced by the vertical velocity derived from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The 3D cloud-resolving modeling is based on the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) simulation of Typhoon Nari (in 2001). The analysis of the hourly moisture and cloud budgets of the 2D simulation shows that the total moisture source (surface evaporation and vertically integrated moisture convergence) is converted into hydrometeors through vapor condensation and deposition rates regardless of the area size where the average is taken. This leads to the conclusion that the large-scale and cloud-microphysics precipitation efficiencies are statistically equivalent. Results further show that convergence (divergence) of hydrometeors would make precipitation efficiency larger (smaller). The precipitation efficiency tends to be larger (even >100%) in light rain conditions as a result of hydrometeor convergence from the neighboring atmospheric columns. Analysis of the hourly moisture and cloud budgets of the 3D results from the simulation of a typhoon system with heavy rainfall generally supports that of 2D results from the simulation of the tropical convective system with moderate rainfall intensity.

scholarly journals Transition between Suppressed and Active Phases of Intraseasonal Oscillations in the Indo-Pacific Warm Pool

2006 ◽  
Vol 19 (21) ◽  
pp. 5519-5530 ◽  
Author(s):  
P. A. Agudelo ◽  
J. A. Curry ◽  
C. D. Hoyos ◽  
P. J. Webster
Keyword(s):  
Large Scale ◽  
Transition Period ◽  
Numerical Models ◽  
Convective Available Potential Energy ◽  
Lower Troposphere ◽  
Diagnostic Study ◽  
Tropical Ocean ◽  
Toga Coare ◽  
Ocean Atmosphere ◽  
Intraseasonal Oscillations

Abstract Intraseasonal oscillations (ISOs) are important large-amplitude and large-scale elements of the tropical Indo-Pacific climate with time scales in the 20–60-day period range, during which time they modulate higher-frequency tropical weather. Despite their importance, the ISO is poorly simulated and predicted by numerical models. A joint diagnostic and modeling study of the ISO is conducted, concentrating on the period between the suppressed and active (referred to as the “transition”) period that is hypothesized to be the defining stage for the development of the intraseasonal mode and the component that is most poorly simulated. The diagnostic study uses data from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). It is found that during the transition period, the ocean and the atmosphere undergo gradual but large-scale and high-amplitude changes, especially the moistening of the lower troposphere caused jointly by the anomalously warm sea surface temperature arising from minimal cloud and low winds during the suppressed phase and the large-scale subsidence that inhibits the formation of locally deep convection. Using a cloud classification scheme based on microwave and infrared satellite data, it is observed that midtop (cloud with a top in the middle troposphere) nonprecipitating clouds are a direct response of the low-level moisture buildup. To investigate the sensitivity of ISO simulations to the transitional phase, the European Centre for Medium-Range Weather Forecasts (ECMWF) coupled ocean–atmosphere climate model is used. The ECMWF was run serially in predictive ensemble mode (five members) for 30-day periods starting from 1 December 1992 to 30 January 1993, encompassing the ISO occurring in late December. Predictability of the active convective period of the ISO is poor when initialized before the transitional phases of the ISO. However, when initialized with the correct lower-tropospheric moisture field, predictability increases substantially, although the model convective parameterization appears to trigger convection too quickly without allowing an adequate buildup of convective available potential energy during the transition period.

scholarly journals Convective Organization in Evolving Large-Scale Forcing Represented by a Highly Truncated Numerical Archetype

2018 ◽  
Vol 75 (8) ◽  
pp. 2827-2847 ◽  
Author(s):  
Jun-Ichi Yano ◽  
Mitchell W. Moncrieff
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Momentum Transport ◽  
Phase Iii ◽  
Cold Pools ◽  
Time Period ◽  
Toga Coare ◽  
Data Source ◽  
Convective Momentum Transport ◽  
Convection Parameterization

Abstract Considered as a prognostic generalization of mass-flux-based convection parameterization, the highly truncated nonhydrostatic anelastic model with segmentally constant approximation (NAM–SCA) is tested with time-evolving large-scale forcing. The 20-day GATE Phase III period is taken as a major data source. The main advantage of the NAM–SCA parameterization is consistency with subgrid-scale dynamics as represented by the nonhydrostatic anelastic formulation. The approach explicitly generates important dynamical structures of convection (e.g., mesoscale circulations, cold pools) spontaneously without further tuning or treatment as additional subcomponents. As with other convection parameterizations, the numerical simulation of the precipitation rate, the apparent heat source, and the apparent moisture sink is straightforward and reasonably insensitive to the numerical procedures. However, convective momentum transport by organized convection turns out to be difficult even with NAM–SCA, especially for the inherently three-dimensional shear-parallel systems. Modifications of NAM–SCA regarding the large-scale forcing formulation improves the mesoscale momentum transport. Simulation of the full 120-day TOGA COARE period demonstrates the performance of NAM–SCA in different meteorological conditions and its capacity to operate over a longer time period.

scholarly journals Review of Aerosol–Cloud Interactions: Mechanisms, Significance, and Challenges

2016 ◽  
Vol 73 (11) ◽  
pp. 4221-4252 ◽  
Author(s):  
Jiwen Fan ◽  
Yuan Wang ◽  
Daniel Rosenfeld ◽  
Xiaohong Liu
Keyword(s):  
Radiative Forcing ◽  
Large Scale ◽  
Dynamic Properties ◽  
Global Climate ◽  
Spatial Scales ◽  
Cloud Microphysics ◽  
Large Variability ◽  
Spatial And Temporal Scales ◽  
Aerosol Cloud ◽  
Aerosol Cloud Interactions

Abstract Over the past decade, the number of studies that investigate aerosol–cloud interactions has increased considerably. Although tremendous progress has been made to improve the understanding of basic physical mechanisms of aerosol–cloud interactions and reduce their uncertainties in climate forcing, there is still poor understanding of 1) some of the mechanisms that interact with each other over multiple spatial and temporal scales, 2) the feedbacks between microphysical and dynamical processes and between local-scale processes and large-scale circulations, and 3) the significance of cloud–aerosol interactions on weather systems as well as regional and global climate. This review focuses on recent theoretical studies and important mechanisms on aerosol–cloud interactions and discusses the significances of aerosol impacts on radiative forcing and precipitation extremes associated with different cloud systems. The authors summarize the main obstacles preventing the science from making a leap—for example, the lack of concurrent profile measurements of cloud dynamics, microphysics, and aerosols over a wide region on the observation side and the large variability of cloud microphysics parameterizations resulting in a large spread of modeling results on the modeling side. Therefore, large efforts are needed to escalate understanding. Future directions should focus on obtaining concurrent measurements of aerosol properties and cloud microphysical and dynamic properties over a range of temporal and spatial scales collected over typical climate regimes and closure studies, as well as improving understanding and parameterizations of cloud microphysics such as ice nucleation, mixed-phase properties, and hydrometeor size and fall speed.

scholarly journals Prediction and Diagnosis of Tropical Cyclone Formation in an NWP System. Part I: The Critical Role of Vortex Enhancement in Deep Convection

2006 ◽  
Vol 63 (12) ◽  
pp. 3077-3090 ◽  
Author(s):  
K. J. Tory ◽  
M. T. Montgomery ◽  
N. E. Davidson
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Deep Convection ◽  
Weather Prediction ◽  
Critical Role ◽  
Research Programme ◽  
Limited Area ◽  
Tropical Ocean ◽  
Enhancement Mechanism ◽  
Toga Coare

This is the first of a three-part investigation into tropical cyclone (TC) genesis in the Australian Bureau of Meteorology’s Tropical Cyclone Limited Area Prediction System (TC-LAPS), an operational numerical weather prediction (NWP) forecast model. The primary TC-LAPS vortex enhancement mechanism is presented in Part I, the entire genesis process is illustrated in Part II using a single TC-LAPS simulation, and in Part III a number of simulations are presented exploring the sensitivity and variability of genesis forecasts in TC-LAPS. The primary vortex enhancement mechanism in TC-LAPS is found to be convergence/stretching and vertical advection of absolute vorticity in deep intense updrafts, which result in deep vortex cores of 60–100 km in diameter (the minimum resolvable scale is limited by the 0.15° horizontal grid spacing). On the basis of the results presented, it is hypothesized that updrafts of this scale adequately represent mean vertical motions in real TC genesis convective regions, and perhaps that explicitly resolving the individual convective processes may not be necessary for qualitative TC genesis forecasts. Although observations of sufficient spatial and temporal resolution do not currently exist to support or refute this proposition, relatively large-scale (30 km and greater), lower- to midlevel tropospheric convergent regions have been observed in tropical oceanic environments during the Global Atmospheric Research Programme (GARP) Atlantic Tropical Experiment (GATE), the Equatorial Mesoscale Experiment (EMEX), and the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE), and regions of extreme convection of the order of 50 km are often (remotely) observed in TC genesis environments. These vortex cores are fundamental for genesis in TC-LAPS. They interact to form larger cores, and provide net heating that drives the system-scale secondary circulation, which enhances vorticity on the system scale akin to the classical Eliassen problem of a balanced vortex driven by heat sources. These secondary vortex enhancement mechanisms are documented in Part II. In some recent TC genesis theories featured in the literature, vortex enhancement in deep convective regions of mesoscale convective systems (MCSs) has largely been ignored. Instead, they focus on the stratiform regions. While it is recognized that vortex enhancement through midlevel convergence into the stratiform precipitation deck can greatly enhance midtropospheric cyclonic vorticity, it is suggested here that this mechanism only increases the potential for genesis, whereas vortex enhancement through low- to midlevel convergence into deep convective regions is necessary for genesis.

scholarly journals Measuring Taxi Accessibility Using Grid-Based Method with Trajectory Data

2018 ◽  
Vol 10 (9) ◽  
pp. 3187 ◽  
Author(s):  
Shixiong Jiang ◽  
Wei Guan ◽  
Zhengbing He ◽  
Liu Yang
Keyword(s):  
Large Scale ◽  
Grid Cells ◽  
Trajectory Data ◽  
Late Night ◽  
Time Period ◽  
Time Periods ◽  
Highly Correlated ◽  
The Given ◽  
Beijing China ◽  
Grid Based

Accessibility has drawn extensive attention from city planners and transportation researchers for decades. With the benefits of large-scale and varying time, this study aims to combine the taxi global positioning system (GPS) data with a cumulative opportunity measure to calculate taxi accessibility in Beijing, China. As traffic conditions vary significantly over time and space, we select four typical time periods and introduce a grid-based method to divide the study area into grid cells. Both the GPS signals and opportunities that include the constant points of interest, total drop-offs, and dynamic drop-offs, are aggregated in these grid cells. The cumulative opportunity measure counts all reachable grid cells within the given travel time threshold, along with the corresponding opportunities. The results demonstrate that the accessibility varies in the four time periods, with better performance seen in the late-night hours. Although the spatial distributions of the three kinds of opportunities are different, these accessibilities show great similarity. In addition, the relative accessibilities of different measures are highly correlated. In general, grid cells with higher accessibilities in one time period are likely to also have higher accessibilities in other time periods. Moreover, the results suggest that taxi accessibility can be measured from its trajectory data only.

scholarly journals A Study of the Response of Deep Tropical Clouds to Large-Scale Thermodynamic Forcings. Part II: Sensitivities to Microphysics, Radiation, and Surface Fluxes

2007 ◽  
Vol 64 (3) ◽  
pp. 869-886 ◽  
Author(s):  
D. E. Johnson ◽  
W-K. Tao ◽  
J. Simpson
Keyword(s):  
Large Scale ◽  
Longwave Radiation ◽  
Surface Fluxes ◽  
Tropical Ocean ◽  
Surface Precipitation ◽  
Mass Fluxes ◽  
Toga Coare ◽  
The Mean ◽  
Thermodynamics And Dynamics ◽  
Microphysical Processes

Abstract The Goddard Cumulus Ensemble (GCE) model is used to examine the sensitivities of multiday 2D simulations of deep tropical convection to surface fluxes, interactive radiation, and ice microphysical processes. The simulations incorporate large-scale temperature, moisture, and momentum forcings, from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) for the period 19–27 December 1992. This study shows that, when surface fluxes are eliminated, the mean simulated atmosphere is much cooler and drier, convection and CAPE are much weaker, precipitation is less, and low-level to midlevel cloudiness is much greater. Surface fluxes using the TOGA COARE flux algorithm are weaker than with the aerodynamic formulation, but closer to the observed fluxes. In addition, trends similar to those noted above for the case without surface fluxes are produced for the TOGA COARE flux case, albeit to a much lesser extent. The elimination of shortwave and longwave radiation is found to have only minimal effects on the mean thermodynamics, convection, and precipitation. However, exclusion of radiation in the model does have a significant impact on cloud temperatures and structure above 200 mb. The removal of ice microphysical processes produces major changes in the structure of the clouds. Much of the liquid water is transported to the upper levels of the troposphere and evaporates, resulting in less mean total surface precipitation. The precipitation primarily occurs in regions of narrow, but intense, convective rainfall bands. The elimination of melting processes (diabatic cooling and conversions to rain) leads to greater (ice) hydrometeor mass below the 0°C level and reduced latent cooling. This, along with weaker vertical cloud mass fluxes, produces a much warmer and moister boundary layer, and a greater mean CAPE. Finally, the elimination of the graupel species has only a small impact on mean total precipitation, thermodynamics, and dynamics of the simulation, but does produce much greater snow mass just above the melting layer.

scholarly journals Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance

2017 ◽  
Vol 114 (31) ◽  
pp. 8301-8306 ◽  
Author(s):  
Jan Geert Hiddink ◽  
Simon Jennings ◽  
Marija Sciberras ◽  
Claire L. Szostek ◽  
Kathryn M. Hughes ◽  
...  
Keyword(s):  
High Resolution ◽  
Penetration Depth ◽  
Comparative Studies ◽  
Large Scale ◽  
Global Analysis ◽  
Spatial Scales ◽  
Recovery Rates ◽  
Bottom Trawling ◽  
Recovery Times ◽  
Highly Correlated

Bottom trawling is the most widespread human activity affecting seabed habitats. Here, we collate all available data for experimental and comparative studies of trawling impacts on whole communities of seabed macroinvertebrates on sedimentary habitats and develop widely applicable methods to estimate depletion and recovery rates of biota after trawling. Depletion of biota and trawl penetration into the seabed are highly correlated. Otter trawls caused the least depletion, removing 6% of biota per pass and penetrating the seabed on average down to 2.4 cm, whereas hydraulic dredges caused the most depletion, removing 41% of biota and penetrating the seabed on average 16.1 cm. Median recovery times posttrawling (from 50 to 95% of unimpacted biomass) ranged between 1.9 and 6.4 y. By accounting for the effects of penetration depth, environmental variation, and uncertainty, the models explained much of the variability of depletion and recovery estimates from single studies. Coupled with large-scale, high-resolution maps of trawling frequency and habitat, our estimates of depletion and recovery rates enable the assessment of trawling impacts on unprecedented spatial scales.

scholarly journals Cloud-Resolving Model Simulations over the ARM SGP

2007 ◽  
Vol 135 (8) ◽  
pp. 2841-2853 ◽  
Author(s):  
Xiaoqing Wu ◽  
Xin-Zhong Liang ◽  
Sunwook Park
Keyword(s):  
Great Plains ◽  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Heat Fluxes ◽  
Heating Rates ◽  
Tropical Ocean ◽  
Radiative Fluxes ◽  
Toga Coare ◽  
Cloud Resolving Model

Abstract This study aims to combine the cloud-resolving model (CRM) simulations with the Department of Energy’s Atmospheric Radiation Measurement Program (ARM) observations to provide long-term comprehensive and physically consistent data that facilitate quantifying the effects of subgrid cloud–radiation interactions and ultimately to develop physically based parameterization of these interactions in general circulation models. The CRM is applied here to simulate the midlatitude cloud systems observed at the ARM southern Great Plains (SGP) site during the 1997 intensive observation period. As in the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE), the CRM-simulated ensemble mean quantities such as cloud liquid water, cloud fraction, precipitation, and radiative fluxes are generally in line with the surface measurements, satellite, and radar retrievals. The CRM differences from the ARM estimates, when averaged over the entire period, are less than 5 W m−2 in both longwave and shortwave radiative fluxes at the top of the atmosphere and surface. Because of the different large-scale forcing and surface heat fluxes in ARM and TOGA COARE, the CRM produces different cloud distributions over the midlatitude continent and tropical ocean. However, diagnostic analyses show that the subgrid cloud variability has similar impact on the domain-averaged radiative fluxes and heating rates in ARM as in TOGA COARE.

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