scholarly journals Diabatic processes modulating the vertical structure of the jet stream above the cold front of an extratropical cyclone: sensitivity to deep convection schemes

2021 ◽  
Author(s):  
Meryl Wimmer ◽  
Gwendal Rivière ◽  
Philippe Arbogast ◽  
Jean-Marcel Piriou ◽  
Julien Delanoë ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Cold Front ◽  
Deep Convection ◽  
Weather Prediction ◽  
Extratropical Cyclone ◽  
Jet Stream ◽  
Convection Scheme ◽  
Cold Air ◽  
Middle Troposphere ◽  
Pv Gradient

Abstract. The effect of deep convection parameterization on the jet stream above the cold front of an explosive extratropical cyclone is investigated in the global numerical weather prediction model ARPEGE, operational at Météo-France. Two hindcast simulations differing only in the deep convection scheme used are systematically compared with each other, with (re)-analysis datasets and with NAWDEX airborne observations. The deep convection representation has an important effect on the vertical structure of the jet stream above the cold front at one-day lead time. The simulation with the less active scheme shows a deeper jet stream, associated with a stronger potential vorticity (PV) gradient in the jet core in middle troposphere. This is due to a larger deepening of the dynamical tropopause on the cold-air side of the jet and a higher PV destruction on the warm-air side, near 600 hPa. To better understand the origin of this stronger PV gradient, Lagrangian backward trajectories are computed. On the cold-air side of the jet, numerous trajectories undergo a rapid ascent from the boundary layer to the mid levels in the simulation with the less active deep convection scheme, whereas they stay at mid levels in the other simulation. This ascent explains the higher PV noted on that side of the jet in the simulation with the less active deep convection scheme. These ascending air masses form mid-level ice clouds that are not observed in the microphysical retrievals from airborne radar-lidar measurements. On the warm-air side of the jet, in the warm conveyor belt (WCB) ascending region, the Lagrangian trajectories with the less active deep convection scheme undergo a higher PV destruction due to a stronger heating occurring in the lower and middle troposphere. In contrast, in the simulation with the most active deep convection scheme, both the heating and PV destruction extend further up in the upper troposphere.

scholarly journals Investigating the sensitivity of high-resolution mesoscale models to microphysical parameters by the use of polarimetric radar observations

2010 ◽  
Vol 10 (8) ◽  
pp. 20461-20514
Author(s):  
R. Ferretti ◽  
K. De Sanctis ◽  
L. Molini ◽  
A. Parodi ◽  
M. Montopoli ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Weather Prediction ◽  
Radar Data ◽  
Convective Cell ◽  
Polarimetric Radar ◽  
Horizontal Structure ◽  
Po Valley

Abstract. An improved methodology for investigating mesoscale model microphysics is presented and discussed for a case study. Polarimetric radar data are used to assess numerical weather prediction (NWP) model's skill in reproducing the microphysical features of severe rainfall. To this aim, an event of deep convection, developed on 20 May 2003 in the Po Valley (Italy), is analyzed. During the selected case study, two weather radars, sited in Gattatico and San Pietro Capofiume (near Bologna, Italy), detected a deep-convective and hail cell with a large inner graupel core which reached the ground, as was reported by local weather authorities and citizens. A hydrometeor classification algorithm, based on a Bayesian approach and a radar simulator model, are used to retrieve the vertical structure of the storm and characterize its ground effects. These products are used for evaluating the sensitivity of NWP models with respect to the graupel density, described in terms of the intercept parameter of the graupel size distribution and its depositional velocity. To this purpose two mesoscale NWP models, specifically COSMO-LAMI and MM5-V3, are used at high spatial resolution. Their ability in reproducing the vertical and the horizontal structure and the microphysical distribution of the major convective cell is evaluated. Both models show large sensitivity to different microphysical settings and a capability to reproduce fairly well the observed hail cell. Ground-radar reflectivity fields and the hydrometeor vertical structure are correctly simulated by both NWP models as opposed to a failure in reproducing the graupel distribution near the ground.

scholarly journals Impact of Environmental Aerosols on a Developing Extratropical Cyclone in the Superparameterized Community Atmosphere Model

2016 ◽  
Vol 29 (15) ◽  
pp. 5533-5546 ◽  
Author(s):  
Yi Lu ◽  
Yi Deng
Keyword(s):  
Growth Rate ◽  
Cold Front ◽  
Deep Convection ◽  
Regional Climate ◽  
Extratropical Cyclone ◽  
Latent Heating ◽  
Stratiform Cloud ◽  
Community Atmosphere Model ◽  
Moisture Supply ◽  
Atmosphere Model

Abstract The impacts of environmental aerosols on the growth of an extratropical cyclone in a realistic winter flow setting are investigated using the superparameterized Community Atmosphere Model (SP-CAM) where cloud-scale dynamics and thermodynamics are explicitly resolved. An examination of the results from 13 ensemble pairs suggests that the growth rate of the cyclone is temporarily reduced as a result of increased aerosol concentrations. A convection–advection–moisture self-adjustment (CAMS) mechanism of aerosol–cyclone interaction is proposed to explain this finding. Specifically, the weakened growth is unambiguously attributed to the weakening of the cold advection underneath the midtropospheric trough of the cyclone. The weakened cold advection is in turn driven by a decrease of the zonal temperature gradient that is tied to the reduced latent heating in the stratiform cloud region of the cyclone. Invigoration of convection ahead of the cold front by aerosols is found to be directly responsible for a suppressed moisture supply into the stratiform cloud region and thus the reduced latent heating there. The regional climate implications of these results are discussed. Also highlighted is the importance of incorporating aerosol microphysical effects on deep convection in any modeling effort that aims to understand aerosol–circulation interaction at the extratropics.

scholarly journals A Unified Convection Scheme (UNICON). Part I: Formulation

2014 ◽  
Vol 71 (11) ◽  
pp. 3902-3930 ◽  
Author(s):  
Sungsu Park
Keyword(s):  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Horizontal Resolution ◽  
Vertical Transport ◽  
Convective Precipitation ◽  
Cold Pool ◽  
Quasi Equilibrium ◽  
Convection Scheme ◽  
Time Step ◽  
Turbulent Eddies

Abstract The author develops a unified convection scheme (UNICON) that parameterizes relative (i.e., with respect to the grid-mean vertical flow) subgrid vertical transport by nonlocal asymmetric turbulent eddies. UNICON is a process-based model of subgrid convective plumes and mesoscale organized flow without relying on any quasi-equilibrium assumptions such as convective available potential energy (CAPE) or convective inhibition (CIN) closures. In combination with a relative subgrid vertical transport scheme by local symmetric turbulent eddies and a grid-scale advection scheme, UNICON simulates vertical transport of water species and conservative scalars without double counting at any horizontal resolution. UNICON simulates all dry–moist, forced–free, and shallow–deep convection within a single framework in a seamless, consistent, and unified way. It diagnoses the vertical profiles of the macrophysics (fractional area, plume radius, and number density) as well as the microphysics (production and evaporation rates of convective precipitation) and the dynamics (mass flux and vertical velocity) of multiple convective updraft and downdraft plumes. UNICON also prognoses subgrid cold pool and mesoscale organized flow within the planetary boundary layer (PBL) that is forced by evaporation of convective precipitation and accompanying convective downdrafts but damped by surface flux and entrainment at the PBL top. The combined subgrid parameterization of diagnostic convective updraft and downdraft plumes, prognostic subgrid mesoscale organized flow, and the feedback among them remedies the weakness of conventional quasi-steady diagnostic plume models—the lack of plume memory across the time step—allowing UNICON to successfully simulate various transitional phenomena associated with convection (e.g., the diurnal cycle of precipitation and the Madden–Julian oscillation).

scholarly journals RELATIONSHIP BETWEEN HIMAWARI-8-DERIVED OVERSHOOTING TOPS AND EXTREME WEATHER EVENTS IN SOUTHEAST ASIA

2016 ◽  
Vol XLI-B7 ◽  
pp. 325-327
Author(s):  
H. M. Park ◽  
M. A. Kim ◽  
J. Im
Keyword(s):  
Heavy Rainfall ◽  
Rain Rate ◽  
Deep Convection ◽  
Weather Prediction ◽  
Extreme Weather Events ◽  
Strong Wind ◽  
Atmospheric Conditions ◽  
Machine Learning Methods ◽  
Weather Events ◽  
Strong Convection

Severe weathers such as heavy rainfall, floods, strong wind, and lightning are closely related with the strong convection activities of atmosphere. Overshooting tops sometimes occur by deep convection above tropopause, penetrating into the lower stratosphere. Due to its high potential energy, the detection of OT is crucial to understand the climatic phenomena. Satellite images are useful to detect the dynamics of atmospheric conditions using cloud observation. This study used machine learning methods for extracting OTs. The reference cases were built using CloudSat, CALIPSO, and Numerical Weather Prediction (NWP) data with Himawari-8 imagery. As reference cases, 11 OT events were detected. The aim of this study is the investigation of relationship between OTs cases and the occurrences of heavy rainfall. For investigation of OT effects, TRMM daily rain rate data (mm/hr) were collected and averaged at 25 km intervals until 250km from the center of OT cases. As the result, precipitation rate clearly coincides with the distance from the center of OT occurrence.

scholarly journals PostProcessing and Visualization Techniques for Convection-Allowing Ensembles

2019 ◽  
Vol 100 (7) ◽  
pp. 1245-1258 ◽  
Author(s):  
Brett Roberts ◽  
Israel L. Jirak ◽  
Adam J. Clark ◽  
Steven J. Weiss ◽  
John S. Kain
Keyword(s):  
Real Time ◽  
Data Extraction ◽  
Deep Convection ◽  
Weather Prediction ◽  
Ensemble Forecast ◽  
Ensemble Prediction ◽  
Data Volume ◽  
Explicit Simulation ◽  
Prediction Systems ◽  
Visualization Techniques

AbstractSince the early 2000s, growing computing resources for numerical weather prediction (NWP) and scientific advances enabled development and testing of experimental, real-time deterministic convection-allowing models (CAMs). By the late 2000s, continued advancements spurred development of CAM ensemble forecast systems, through which a broad range of successful forecasting applications have been demonstrated. This work has prepared the National Weather Service (NWS) for practical usage of the High Resolution Ensemble Forecast (HREF) system, which was implemented operationally in November 2017. Historically, methods for postprocessing and visualizing products from regional and global ensemble prediction systems (e.g., ensemble means and spaghetti plots) have been applied to fields that provide information on mesoscale to synoptic-scale processes. However, much of the value from CAMs is derived from the explicit simulation of deep convection and associated storm-attribute fields like updraft helicity and simulated reflectivity. Thus, fully exploiting CAM ensembles for forecasting applications has required the development of fundamentally new data extraction, postprocessing, and visualization strategies. In the process, challenges imposed by the immense data volume inherent to these systems required new approaches when considering diverse factors like forecaster interpretation and computational expense. In this article, we review the current state of postprocessing and visualization for CAM ensembles, with a particular focus on forecast applications for severe convective hazards that have been evaluated within NOAA’s Hazardous Weather Testbed. The HREF web viewer implemented at the NWS Storm Prediction Center (SPC) is presented as a prototype for deploying these techniques in real time on a flexible and widely accessible platform.

scholarly journals Driftsonde Observations to Evaluate Numerical Weather Prediction of the Late 2006 African Monsoon

2013 ◽  
Vol 52 (4) ◽  
pp. 974-995 ◽  
Author(s):  
Philippe Drobinski ◽  
Fatima Karbou ◽  
Peter Bauer ◽  
Philippe Cocquerez ◽  
Christophe Lavaysse ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Numerical Weather Prediction ◽  
Vertical Structure ◽  
Weather Prediction ◽  
Meridional Wind ◽  
Numerical Weather Prediction Model ◽  
African Monsoon ◽  
Easterly Waves ◽  
Numerical Weather ◽  
Multidisciplinary Analysis

AbstractDuring the international African Monsoon Multidisciplinary Analysis (AMMA) project, stratospheric balloons carrying gondolas called driftsondes capable of dropping meteorological sondes were deployed over West Africa and the tropical Atlantic Ocean. The goals of the deployment were to test the technology and to study the African easterly waves, which are often the forerunners of hurricanes. Between 29 August and 22 September 2006, 124 sondes were dropped over the seven easterly waves that moved across Africa into the Atlantic between about 10° and 20°N, where almost no in situ vertical information exists. Conditions included waves that developed into Tropical Storm Florence and Hurricanes Gordon and Helene. In this study, a selection of numerical weather prediction model outputs has been compared with the dropsondes to assess the effect of some developments in data assimilation on the quality of analyses and forecasts. By comparing two different versions of the Action de Recherche Petite Echelle Grande Echelle (ARPEGE) model of Météo-France with the dropsondes, first the benefits of the last data assimilation updates are quantified. Then comparisons are carried out using the ARPEGE model and the Integrated Forecast System (IFS) model of the European Centre for Medium-Range Weather Forecasts. It is shown that the two models represent very well the vertical structure of temperature and humidity over both land and sea, and particularly within the Saharan air layer, which displays humidity below 5%–10%. Conversely, the models are less able to represent the vertical structure of the meridional wind. This problem seems to be common to ARPEGE and IFS, and its understanding still requires further investigations.

scholarly journals Initial Tendencies of Cloud Regimes in the Met Office Unified Model

2008 ◽  
Vol 21 (4) ◽  
pp. 833-840 ◽  
Author(s):  
K. D. Williams ◽  
M. E. Brooks
Keyword(s):  
Initial Temperature ◽  
Climate Model ◽  
Deep Convection ◽  
Weather Prediction ◽  
Horizontal Resolution ◽  
Systematic Bias ◽  
Cloud Regime ◽  
Tropical Deep Convection ◽  
Cloud Regimes ◽  
Temperature Tendency

Abstract The Met Office unified forecast–climate model is used to compare the properties of simulated climatological cloud regimes with those produced in short-range forecasts initialized from operational analyses. The regimes are defined as principal clusters of joint cloud-top pressure–optical depth histograms. In general, the cloud regime properties are found to be similar at all forecast times, including the climatological mean. This suggests that weaknesses in the representation of fast local processes are responsible for errors in the simulation of the cloud regimes. The increased horizontal resolution of the model used for numerical weather prediction generally has little impact on the cloud regimes, although the simulation of tropical shallow cumulus is improved, while the relative frequency of tropical deep convection and cirrus compare less favorably with observations. Analysis of the initial temperature tendency profiles for each cloud regime indicates that some of the initial temperature tendency, which leads to a systematic bias in the model climatology, is associated with a particular cloud regime.

A Simple Model of Convective Drafts Accounting for the Perturbation Pressure Term

2019 ◽  
Vol 76 (10) ◽  
pp. 3129-3149 ◽  
Author(s):  
Julien Leger ◽  
Jean-Philippe Lafore ◽  
Jean-Marcel Piriou ◽  
Jean-François Guérémy
Keyword(s):  
Shape Factor ◽  
Deep Convection ◽  
Vertical Wind Shear ◽  
Total Cell ◽  
Convection Scheme ◽  
Eddy Simulation ◽  
Downward Pressure ◽  
Pressure Term ◽  
Large Eddy ◽  
Perturbation Pressure

Abstract A simple anelastic two-column model of convective updraft accounting explicitly for the perturbation pressure term is developed. There is no vertical wind shear in the environment, and two geometries (slab or axial) are possible. A shape factor is introduced to account for transport by a nonuniform horizontal profile of the vertical velocity in the updraft and its environment. The perturbation buoyancy profile being prescribed, three parameters must be prescribed: depth and aspect ratio of the updraft and the total cell size. The model is tested for idealized buoyancy profiles and evaluated against a large-eddy simulation of daytime development of deep convection. The model behavior agrees with our understanding of the perturbation pressure within clouds. The simulated updraft quickly responds to the buoyancy field (~5 min), shorter than the convection time scale, so that a steady model could be developed. Below the updraft core, a downward pressure gradient is simulated allowing the updraft to overcome a barrier of convective inhibition. This model is designed to be implemented in a convection scheme to replace classical drag formulations of the updraft model.

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