scholarly journals Cloud-Resolving Model Simulations of KWAJEX: Model Sensitivities and Comparisons with Satellite and Radar Observations

2007 ◽  
Vol 64 (5) ◽  
pp. 1488-1508 ◽  
Author(s):  
Peter N. Blossey ◽  
Christopher S. Bretherton ◽  
Jasmine Cetrone ◽  
Marat Kharoutdinov
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Longwave Radiation ◽  
Radiative Fluxes ◽  
Model Simulations ◽  
Time Period ◽  
Ground Validation ◽  
Cloud Resolving Model ◽  
Sensitivity Studies ◽  
Upper Level

Abstract Three-dimensional cloud-resolving model simulations of a mesoscale region around Kwajalein Island during the Kwajalein Experiment (KWAJEX) are performed. Using observed winds along with surface and large-scale thermodynamic forcings, the model tracks the observed mean thermodynamic soundings without thermodynamic nudging during 52-day simulations spanning the whole experiment time period, 24 July–14 September 1999. Detailed comparisons of the results with cloud and precipitation observations, including radar reflectivities from the Kwajalein ground validation radar and International Satellite Cloud Climatology Project (ISCCP) cloud amounts and radiative fluxes, reveal the biases and sensitivities of the model’s simulated clouds. The amount and optical depth of high cloud are underpredicted by the model during less rainy periods, leading to excessive outgoing longwave radiation (OLR) and insufficient albedo. The simulated radar reflectivities tend to be excessive, especially in the upper troposphere, suggesting that simulated high clouds are precipitating large hydrometeors too efficiently. Occasionally, large-scale advective forcing errors also seem to contribute to upper-level cloud and relative humidity biases. An extensive suite of sensitivity studies to different microphysical and radiative parameterizations is performed, with surprisingly little impact on the results in most cases.

scholarly journals tobac 1.2: towards a flexible framework for tracking and analysis of clouds in diverse datasets

2019 ◽  
Vol 12 (11) ◽  
pp. 4551-4570 ◽  
Author(s):  
Max Heikenfeld ◽  
Peter J. Marinescu ◽  
Matthew Christensen ◽  
Duncan Watson-Parris ◽  
Fabian Senf ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Longwave Radiation ◽  
Geostationary Satellite ◽  
Model Assessment ◽  
Model Simulations ◽  
Cloud Properties ◽  
Level Data ◽  
Different Types ◽  
Cloud Resolving Model ◽  
High Level

Abstract. We introduce tobac (Tracking and Object-Based Analysis of Clouds), a newly developed framework for tracking and analysing individual clouds in different types of datasets, such as cloud-resolving model simulations and geostationary satellite retrievals. The software has been designed to be used flexibly with any two- or three-dimensional time-varying input. The application of high-level data formats, such as Iris cubes or xarray arrays, for input and output allows for convenient use of metadata in the tracking analysis and visualisation. Comprehensive analysis routines are provided to derive properties like cloud lifetimes or statistics of cloud properties along with tools to visualise the results in a convenient way. The application of tobac is presented in two examples. We first track and analyse scattered deep convective cells based on maximum vertical velocity and the three-dimensional condensate mixing ratio field in cloud-resolving model simulations. We also investigate the performance of the tracking algorithm for different choices of time resolution of the model output. In the second application, we show how the framework can be used to effectively combine information from two different types of datasets by simultaneously tracking convective clouds in model simulations and in geostationary satellite images based on outgoing longwave radiation. The tobac framework provides a flexible new way to include the evolution of the characteristics of individual clouds in a range of important analyses like model intercomparison studies or model assessment based on observational data.

scholarly journals tobac v1.0: towards a flexible framework for tracking and analysis of clouds in diverse datasets

2019 ◽  
Author(s):  
Max Heikenfeld ◽  
Peter J. Marinescu ◽  
Matthew Christensen ◽  
Duncan Watson-Parris ◽  
Fabian Senf ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Longwave Radiation ◽  
Geostationary Satellite ◽  
Model Assessment ◽  
Model Simulations ◽  
Cloud Properties ◽  
Level Data ◽  
Different Types ◽  
Cloud Resolving Model ◽  
High Level

Abstract. We introduce tobac (Tracking and Object-Based Analysis of Clouds), a newly developed framework for tracking and analysing individual clouds in different types of datasets, such as cloud-resolving model simulations and geostationary satellite retrievals. The software has been designed to be used flexibly with any two- or three-dimensional time-varying input. The application of high-level data formats, such as iris cubes or xarray arrays, for input and output allows for convenient use of metadata in the tracking analysis and visualisation. Comprehensive analysis routines are provided to derive properties like cloud lifetimes or statistics of cloud properties along with tools to visualise the results in a convenient way. The application of tobac is presented in two examples. We first track and analyse scattered deep convective cells based on maximum vertical velocity and the three-dimensional condensate mixing ratio field in cloud-resolving model simulations. We also investigate the performance of the tracking algorithm for different choices of time resolution of the model output. In the second application, we show how the framework can be used to effectively combine information from two different types of datasets by simultaneously tracking convective clouds in model simulations and in geostationary satellite images based on outgoing longwave radiation. tobac provides a flexible new way to include the evolution of the characteristics of individual clouds in a range of important analyses like model intercomparison studies or model assessment based on observational data.

A Test of the Simulation of Tropical Convective Cloudiness by a Cloud-Resolving Model

2009 ◽  
Vol 22 (11) ◽  
pp. 2834-2849 ◽  
Author(s):  
Mario A. Lopez ◽  
Dennis L. Hartmann ◽  
Peter N. Blossey ◽  
Robert Wood ◽  
Christopher S. Bretherton ◽  
...  
Keyword(s):  
Rain Rate ◽  
Strong Dependence ◽  
Three Dimensional ◽  
Longwave Radiation ◽  
Physical Parameters ◽  
Model Parameters ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Cloud Resolving Model ◽  
Upper Level

Abstract A methodology is described for testing the simulation of tropical convective clouds by models through comparison with observations of clouds and precipitation from earth-orbiting satellites. Clouds are divided into categories that represent convective cores: moderately thick anvil clouds and thin high clouds. Fractional abundances of these clouds are computed as a function of rain rate. A three-dimensional model is forced with steady forcing characteristics of tropical Pacific convective regions, and the model clouds are compared with satellite observations for the same regions. The model produces a good simulation of the relationship between the precipitation rate and optically thick cold clouds that represent convective cores. The observations show large abundances of anvil cloud with a strong dependence on rain rate, but the model produces too little anvil cloud by a factor of about 4 and with a very weak dependence on the rain rate. The observations also show probability density functions for outgoing longwave radiation (OLR) and albedo with maxima that correspond to extended upper-level cold clouds, whereas the model does not. The sensitivity of the anvil cloud simulation to model parameters is explored using a two-dimensional model. Both cloud physical parameters and mean wind shear effects are investigated. The simulation of anvil cloud can be improved while maintaining a good simulation of optically thick cloud by adjusting the cloud physics parameters in the model to produce more ice cloud and less liquid water cloud.

scholarly journals An Initiation Process of Tropical Depression-type Disturbances under the Influence of Upper-level Troughs

2021 ◽  
Author(s):  
Yuya Hamaguchi ◽  
Yukari N. Takayabu
Keyword(s):  
Large Scale ◽  
Convective Available Potential Energy ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Dimensional Structure ◽  
Convective Heating ◽  
Upper Troposphere ◽  
Tropical Depression ◽  
Upper Level ◽  
Extratropical Forcing

AbstractIn this study, the statistical relationship between tropical upper-tropospheric troughs (TUTTs) and the initiation of summertime tropical-depression type disturbances (TDDs) over the western and central North Pacific is investigated. By applying a spatiotemporal filter to the 34-year record of brightness temperature and using JRA-55 reanalysis products, TDD-event initiations are detected and classified as trough-related (TR) or non-trough-related (non-TR). The conventional understanding is that TDDs originate primarily in the lower-troposphere; our results refine this view by revealing that approximately 30% of TDDs in the 10°N-20°N latitude ranges are generated under the influence of TUTTs. Lead-lag composite analysis of both TR- and non-TR-TDDs clarifies that TR-TDDs occur under relatively dry and less convergent large-scale conditions in the lower-troposphere. This result suggests that TR-TDDs can form in a relatively unfavorable low-level environment. The three-dimensional structure of the wave activity flux reveals southward and downward propagation of wave energy in the upper troposphere that converges at the mid-troposphere around the region where TR-TDDs occur, suggesting the existence of extratropical forcing. Further, the role of dynamic forcing associated with the TUTT on the TR-TDD-initiation is analyzed using the quasi-geostrophic omega equation. The result reveals that moistening in the mid-to-upper troposphere takes place in association with the sustained dynamical ascent at the southeast side of the TUTT, which precedes the occurrence of deep convective heating. Along with a higher convective available potential energy due to the destabilizing effect of TUTTs, the moistening in the mid-to-upper troposphere also helps to prepare the environment favorable to TDDs initiation.

Factors Controlling Multiple Tropical Cyclone Events in the Western North Pacific*

2011 ◽  
Vol 139 (3) ◽  
pp. 885-894 ◽  
Author(s):  
Jianyun Gao ◽  
Tim Li
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Outgoing Longwave Radiation ◽  
Western North Pacific ◽  
Large Scale ◽  
Longwave Radiation ◽  
Active Phase ◽  
Spatial Distance ◽  
Interannual Time Scale ◽  
Upper Level

Abstract The statistical feature of occurrence of multiple tropical cyclone (MTC) events in the western North Pacific (WNP) is examined during summer (June–September) for the period of 1979–2006. The number of MTC events ranged from one to eight per year, experiencing a marked interannual variation. The spatial distance between the TCs associated with MTC events is mostly less than 3000 km, which accounts for 73% of total samples. The longest active phase of an MTC event lasts for nine days, and about 80% of the MTC events last for five days or less. A composite analysis of active and inactive MTC phases reveals that positive low-level (negative upper-level) vorticity anomalies and enhanced convection and midtropospheric relative humidity are the favorable large-scale conditions for MTC genesis. About 77% of the MTC events occurred in the region where either the atmospheric intraseasonal (25–70 day) oscillation (ISO) or biweekly (10–20 day) oscillation (BWO) is in a wet phase. The overall occurrence of the MTC events is greatly regulated by the combined large-scale impact of BWO, ISO, and the lower-frequency (90 days or longer) oscillation. On the interannual time scale, the MTC frequency is closely related to the seasonal mean anomalies of 850-hPa vorticity, outgoing longwave radiation (OLR), and 500-hPa humidity fields. The combined ISO and BWO activity is greatly strengthened (weakened) in the WNP region during the MTC active (inactive) years.

scholarly journals MJO Moisture Budget during DYNAMO in a Cloud-Resolving Model

2016 ◽  
Vol 73 (6) ◽  
pp. 2257-2278 ◽  
Author(s):  
Matthew A. Janiga ◽  
Chidong Zhang
Keyword(s):  
Large Scale ◽  
Moisture Gradient ◽  
Moisture Budget ◽  
Physical Processes ◽  
Low Level ◽  
Moisture Advection ◽  
Stratiform Clouds ◽  
Cloud Resolving Model ◽  
Eddy Transport ◽  
Upper Level

Abstract Contributions by different physical processes and cloud types to the sum of the large-scale vertical moisture advection and apparent moisture sink observed by the DYNAMO field campaign northern sounding array during the passage of a Madden–Julian oscillation (MJO) event are estimated using a cloud-resolving model. The sum of these two moisture budget terms is referred to as the column-confined moisture tendency MC. Assuming diabatic balance, the contribution of different physical processes and cloud types to the large-scale vertical velocity and MC can be estimated using simulated diabatic tendencies and the domain-averaged static stability and vertical moisture gradient. Low-level moistening preceding MJO passage is captured by MC and dominated by the effects of shallow clouds. Because of the large vertical moisture gradient at this level, condensational heating in these clouds generates ascent and vertical moisture advection overwhelming the removal of water vapor by condensation. Shallow convective eddy transport also contributes to low-level moistening during this period. Eddy transport by congestus and deep convective clouds contributes to subsequent mid- and upper-level moistening, respectively, as well as low-level drying. Because the upper-level vertical moisture gradient is small, ice deposition within stratiform clouds has a net drying effect. The weak eddy transport in stratiform clouds is unable to compensate for this drying. Nonprecipitating clouds mainly modulate MC through their effects on radiation. During the enhanced phase, reduced longwave cooling results in less subsidence and drying; the opposite occurs during the suppressed phase. Large-scale horizontal advection, which is not included in MC, is responsible for much of the drying during the dissipating phase.

scholarly journals Numerical Simulations of Sheared Conditionally Unstable Flows over a Mountain Ridge

2014 ◽  
Vol 71 (5) ◽  
pp. 1747-1762 ◽  
Author(s):  
Mario Marcello Miglietta ◽  
Richard Rotunno
Keyword(s):  
Numerical Simulations ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Cold Pool ◽  
Low Level ◽  
Narrow Region ◽  
Cloud Resolving Model ◽  
Upper Level ◽  
Wind Profiles ◽  
Rain Rates

Abstract In two recent papers, the authors performed numerical simulations with a three-dimensional, explicitly cloud-resolving model for a uniform wind flowing past a bell-shaped ridge and using an idealized unstable (Weisman–Klemp) sounding with prescribed values of the relevant parameters. More recently, some observed cases of orographically forced wind profiles were analyzed, showing that, in order to reproduce larger rainfall rates, it was necessary to initialize the sounding with low-level flow toward the mountain with weak flow aloft (as observed). Additional experiments using the Weisman–Klemp sounding, but with nonuniform wind profiles, are performed here to identify the conditions in which the presence of a low-level cross-mountain flow together with calm flow aloft may increase the rain rates in conditionally unstable flows over the orography. The sensitivity of the solutions to the wind speed at the bottom and the top of a shear layer and the effect of different mountain widths and heights are systematically analyzed herein. Large rainfall rates are obtained when the cold pool, caused by the evaporative cooling of rain from precipitating convective clouds, remains quasi stationary upstream of the mountain peak. This condition occurs when the cold-pool propagation is approximately countered by the environmental wind. The large precipitation amounts can be attributed to weak upper-level flow, which favors stronger updrafts and upright convective cells, and to the ground-relative stationarity of the cells. This solution feature is produced with ambient wind shear within a narrow region of the parameter space explored here and does not occur in the numerical solutions obtained in the authors’ previous studies with uniform wind profiles.

Simulating the Interaction between a Straight Boundary and a Particle

2004 ◽  
Vol 467-470 ◽  
pp. 1105-1110
Author(s):  
B. Radhakrishnan ◽  
G.B. Sarma
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Energy Difference ◽  
Interaction Force ◽  
Lattice Temperature ◽  
Stored Energy ◽  
Theoretical Limit ◽  
Interface Position ◽  
Model Simulations ◽  
Boundary Velocity

The paper describes large scale, three-dimensional, Potts model simulations of the interaction between a coarse particle and a straight boundary driven by a bulk stored energy difference across the boundary. It is shown that the variation of the interaction energy as a function of the interface position is significantly affected by the choice of the lattice temperature. The maximum force offered by the particle on the grain boundary decreases with increasing lattice temperature and approaches the theoretical limit at high lattice temperatures. The boundary velocity responds appropriately to changes in the magnitude and direction of the interaction force only at high lattice temperatures.

scholarly journals Impacts of increasing the aerosol complexity in the Met Office global NWP model

2013 ◽  
Vol 13 (11) ◽  
pp. 30453-30520 ◽  
Author(s):  
J. P. Mulcahy ◽  
D. N. Walters ◽  
N. Bellouin ◽  
S. F. Milton
Keyword(s):  
West Africa ◽  
Direct Effect ◽  
Forest Fires ◽  
Short Range ◽  
Large Scale ◽  
Weather Prediction ◽  
Three Dimensional ◽  
Longwave Radiation ◽  
Dust Storms ◽  
Surface Radiation

Abstract. Inclusion of the direct and indirect radiative effects of aerosols in high resolution global numerical weather prediction (NWP) models is being increasingly recognised as important for the improved accuracy of short-range weather forecasts. In this study the impacts of increasing the aerosol complexity in the global NWP configuration of the Met Office Unified Model (MetUM) are investigated. A hierarchy of aerosol representations are evaluated including three dimensional monthly mean speciated aerosol climatologies, fully prognostic aerosols modelled using the CLASSIC aerosol scheme and finally, initialised aerosols using assimilated aerosol fields from the GEMS project. The prognostic aerosol schemes are better able to predict the temporal and spatial variation of atmospheric aerosol optical depth, which is particularly important in cases of large sporadic aerosol events such as large dust storms or forest fires. Including the direct effect of aerosols improves model biases in outgoing longwave radiation over West Africa due to a better representation of dust. However, uncertainties in dust optical properties propogate to its direct effect and the subsequent model response. Inclusion of the indirect aerosol effects improves surface radiation biases at the North Slope of Alaska ARM site due to lower cloud amounts in high latitude clean air regions. This leads to improved temperature and height forecasts in this region. Impacts on the global mean model precipitation and large-scale circulation fields were found to be generally small in the short range forecasts. However, the indirect aerosol effect leads to a strengthening of the low level monsoon flow over the Arabian Sea and Bay of Bengal and an increase in precipitation over Southeast Asia. Regional impacts on the African Easterly Jet (AEJ) are also presented with the large dust loading in the aerosol climatology enhancing of the heat low over West Africa and weakening the AEJ. This study highlights the importance of including a~more realistic treatment of aerosol-cloud interactions in global NWP models and the potential for improved global environmental prediction systems through the incorporation of more complex aerosol schemes.

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