A Numerical Study of the Stratiform Region of a Fast-Moving Squall Line. Part I: General Description and Water and Heat Budgets

The pre-summer heavy rainfall over southern China during 3-8 June 2008 is simulated using a two-dimensional cloud-resolving model. The model is integrated with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature and vapour advection from National Centers for Environmental Prediction (NCEP)/Global Data Assimilation System (GDAS) data. The effects of vertical wind shear and cloud radiative processes on the response of rainfall to largescale forcing are analysed through the comparison of two sensitivity experiments with the control experiment. One sensitivity experiment excludes the large-scale vertical wind shear and the other excludes the cloud radiative effects. During the decay phase of convection, the increase in model domain-mean surface rain-rate resulting from the exclusion of vertical wind shear is associated with the slowdown in the decrease of perturbation kinetic energy due to the exclusion of barotropic conversion from mean kinetic energy to perturbation kinetic energy. The increase in domain-mean rain-rate from the exclusion of cloud radiative effects is related to the enhancement of condensation and associated latent heat as a result of strengthened radiative cooling. The increase in the domain-mean surface rain-rate is mainly associated with the increase of convective rainfall, which is in turn related to the local atmospheric change from moistening to drying. During the onset and mature phases of convection, the domain-mean surface rain-rates are generally insensitive to vertical wind shear and cloud radiative effects whereas convective and stratiform rain-rates are sensitive to vertical wind shear and cloud radiative effects. The decrease in convective rain-rate and the increase in stratiform rain-rate are primarily associated with the enhanced transport of hydrometeor concentration from convective regions to raining stratiform regions. Copyright c 2011 Royal Meteorological Society Key Words: cloud-resolving model simulation; convective and stratiform rain-rates; vertical wind shear; cloud radiative effects; budget analysis

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Effects of vertical wind shear and cloud radiative processes on responses of rainfall to the large‐scale forcing during pre‐summer heavy rainfall over southern China

Shen

2011

“…The Meso-NH version used here includes a bulk microphysical scheme (Caniaux et al, 1997;Pinty and Jabouille, 1998) governing the equations of the six water species: water vapour, cloud water, rain water, primary ice, snow aggregates and graupel. The turbulence parametrization models the three-dimensional turbulent fluxes based on a 1.5-order closure (Cuxart et al, 2000) and a mixing length following the method of Bougeault and Lacarrère (1989).…”

Section: Model Set-upmentioning

confidence: 99%

Idealized numerical simulations of quasi‐stationary convective systems over the Northwestern Mediterranean complex terrain

Bresson

Ducrocq

Nuissier

et al. 2012

Northwestern Mediterranean coastal regions are frequently affected by torrential rainfall associated with quasi-stationary mesoscale convective systems (MCSs). The present work examines how the characteristics of a conditionally unstable flow impinging on the coastal complex terrain of the Northwestern Mediterranean can affect the location and intensity of quasi-stationary MCSs. The study is based on idealized simulations, but including the major ingredients of Northwestern Mediterranean heavy precipitation events: a moist conditionally unstable marine flow of about 100 km width facing the true terrain, composed of the Massif Central surrounded by the Alps and the Pyrenees.We find that MCSs are located upstream of the mountain range with a slow flow, whereas with a rapid flow the heaviest precipitation is over the Massif Central slopes. In a similar way, when the lateral environment is drier the heaviest precipitation is located upstream whereas a humid environment favours precipitation over the slopes. The dominant lifting mechanism is strongly related to the location of the system: (1) direct orographic triggering for systems over mountain slopes and (2) cold-pool triggering for upstream systems. In addition, the neighbouring mountains interplay through deflection of the flow and induced low-level convergence favoured by slow or dry lateral environments and through cold-pool blocking within valleys. Copyright c 2012 Royal Meteorological SocietyKey Words: deep convection; heavy precipitation; mesoscale processes

“…AROME uses a nonhydrostatic extension of the limited-area NWP model ALADIN for the adiabatic equations (Bubnová et al, 1995;Bénard, 2004), whereby the vertical coordinate becomes hydrostatic pressure, and two prognostic variables are added: vertical velocity and departure of the pressure from hydrostatic balance. The AROME physical package is extracted from the physical parametrizations of the Meso-NH research model (Lafore et al, 1998): the prognostic equations of the six water species (vapour, cloud water, rain water, primary ice, graupel and snow) are governed by a bulk microphysical scheme (Caniaux et al, 1994) and the deep convection is resolved explicitly. The radiative scheme is the RRTM parametrization (Mlawer et al, 1997) and the turbulence scheme is from Cuxart et al (2000).…”

Section: Assimilation Experimentsmentioning

confidence: 99%

The benefit of GPS zenith delay assimilation to high‐resolution quantitative precipitation forecasts: a case‐study from COPS IOP 9

Yan

Ducrocq

Jaubert

et al. 2009

ABSTRACT:The benefit of assimilating high spatial and temporal resolution Global Positioning System (GPS) zenith tropospheric delay (ZTD) observations within a high-resolution numerical weather prediction (NWP) system is evaluated during IOP 9 of the Convective and Orographically-induced Precipitation Study (COPS) campaign. In the framework of the international COPS field experiment, which took place from June to August 2007, a dense GPS network was deployed in the Vosges mountain region in eastern France and in the Black Forest region in southwestern Germany.GPS ZTD observations collected during the COPS field campaign, in addition to the European operational GPS data, are assimilated into the AROME/3D-Var system. We investigate the impact of assimilating these GPS ZTD observations on the forecast of convective systems that travelled over eastern France during the three days of COPS IOP 9 (18-20 July 2007). The results show a clear positive impact on short-range quantitative precipitation forecasts when GPS ZTD observations are assimilated. The impact is most important on 19 July 2007 (IOP 9b). The present study benefits from additional validation measurements collected during the COPS campaign. In particular we find that the assimilation of ZTD data induces changes in the low-to-middle tropospheric water vapour vertical structure that are consistent with water vapour measurements from radiosonde and airborne lidar.As most of the improvement is gained by assimilating GPS ZTD observations from the European operational GPS network, this study opens up encouraging horizons for the assimilation of GPS ZTD in new high-resolution operational NWP systems.