scholarly journals Adjoint Sensitivity of Surface Precipitation to Initial Conditions

2007 ◽  
Vol 135 (8) ◽  
pp. 2879-2896 ◽  
Author(s):  
Jean-François Mahfouf ◽  
Bernard Bilodeau
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Observation Time ◽  
Specific Humidity ◽  
Convective Precipitation ◽  
Moist Convection ◽  
Variational Assimilation ◽  
Surface Precipitation ◽  
Area Of Interest ◽  
Stratiform Precipitation

Abstract The adjoint version of the Global Environmental Multiscale model including a comprehensive package of simplified and linearized physical processes (large-scale condensation, deep moist convection, vertical diffusion, and subgrid-scale orographic effects) is used to evaluate the sensitivity of surface precipitation to initial conditions for up to 24 h for two meteorological systems: a midlatitude front and a tropical cyclone. Such diagnostics are useful to improve the understanding on variational assimilation of precipitation data. In agreement with a similar study, the largest sensitivity is found with respect to the temperature field for both stratiform and convective precipitation. Close to the observation time and for stratiform precipitation, the sensitivity with respect to specific humidity is rather large, which corroborates conclusions from previous one-dimensional variational data assimilation experimentations. The sensitivity is then reduced significantly after the observation time. The sensitivities of surface precipitation to the wind components and to specific humidity are comparable and are at a maximum at the observation time. The sensitivity to the surface pressure is always much smaller than the sensitivity to the other variables. In general, sensitivities are largest at the observation time and then decrease. However, for the midlatitude perturbation, the sensitivity is enhanced after 12 h for stratiform precipitation and also for convective precipitation using a scheme based on the moisture convergence closure. This results from a dynamical coupling upstream of the area of interest through baroclinic instability as evidenced by vertically backward-tilted sensitivities. Such enhancement is not observed for the tropical case. The tangent-linear approximation remains acceptable for accumulated precipitation up to 24 h but is rather poor for instantaneous rain rates. The variational assimilation of accumulated precipitation should thus be favored.

Genesis of Pre–Hurricane Felix (2007). Part II: Warm Core Formation, Precipitation Evolution, and Predictability

2010 ◽  
Vol 67 (6) ◽  
pp. 1730-1744 ◽  
Author(s):  
Zhuo Wang ◽  
M. T. Montgomery ◽  
T. J. Dunkerton
Keyword(s):  
Initial Conditions ◽  
Numerical Technique ◽  
Transformation Process ◽  
Tropical Storm ◽  
Convective Precipitation ◽  
Moist Convection ◽  
Near Surface ◽  
Warm Core ◽  
Stratiform Precipitation ◽  
Deep Moist Convection

Abstract This is the second of a two-part study examining the simulated formation of Atlantic Hurricane Felix (2007) in a cloud-representing framework. Here several open issues are addressed concerning the formation of the storm’s warm core, the evolution and respective contribution of stratiform versus convective precipitation within the parent wave’s pouch, and the sensitivity of the development pathway reported in Part I to different model physics options and initial conditions. All but one of the experiments include ice microphysics as represented by one of several parameterizations, and the partition of convective versus stratiform precipitation is accomplished using a standard numerical technique based on the high-resolution control experiment. The transition to a warm-core tropical cyclone from an initially cold-core, lower tropospheric wave disturbance is analyzed first. As part of this transformation process, it is shown that deep moist convection is sustained near the pouch center. Both convective and stratiform precipitation rates increase with time. While stratiform precipitation occupies a larger area even at the tropical storm stage, deep moist convection makes a comparable contribution to the total rain rate at the pregenesis stage, and a larger contribution than stratiform processes at the storm stage. The convergence profile averaged near the pouch center is found to become dominantly convective with increasing deep moist convective activity there. Low-level convergence forced by interior diabatic heating plays a key role in forming and intensifying the near-surface closed circulation, while the midlevel convergence associated with stratiform precipitation helps to increase the midlevel circulation and thereby contributes to the formation and upward extension of a tropospheric-deep cyclonic vortex. Sensitivity tests with different model physics options and initial conditions demonstrate a similar pregenesis evolution. These tests suggest that the genesis location of a tropical storm is largely controlled by the parent wave’s critical layer, whereas the genesis time and intensity of the protovortex depend on the details of the mesoscale organization, which is less predictable. Some implications of the findings are discussed.

Physiographic controls on pre-event hydrological states and hydrological response to extreme precipitation in the Alzette River Basin, Luxembourg

2021 ◽  
Author(s):  
Carol Tamez Melendez ◽  
Judith Meyer ◽  
Audrey Douinot ◽  
Günter Blöschl ◽  
Laurent Pfister
Keyword(s):  
River Basin ◽  
Large Scale ◽  
Flash Flood ◽  
Potential Evapotranspiration ◽  
Convective Precipitation ◽  
Hydrological Response ◽  
Local Character ◽  
Area Of Interest ◽  
Oceanic Climate ◽  
Precipitation Events

<p>Flash flood events have caused massive damage on multiple occasions between 2016 and 2018 in several catchments in eastern Luxembourg. This region is very well known for being exposed to large-scale winter floods, commonly triggered by long-lasting advective precipitation events related to westerly atmospheric fluxes. However, flash floods - a truly exceptional phenomenon in this region - are have solely occurred in summer in response to intense convective precipitation events. Thus, because of the rare occurrence and local character of this type of events, the mechanisms eventually controlling a flash flood-type response of a catchment remains poorly understood.  </p><p>Here, we focus on four main objectives: i) the role that physiographic characteristics play on the spatial variability of pre-event hydrological states (as expressed via storage) across a set of 41 nested catchments located in the Sûre River basin (4,240 km<sup>2</sup>), Luxembourg, ii) the hydrological response to precipitation controlled by those pre-event hydrological states, iii) the responsivity (resistance) and elasticity (resilience) of the catchments to global change, and iv) the relation between water yields and the offsets from Budyko curve and its related energy limits.</p><p>The area of interest is not only characterised by a homogenous temperate oceanic climate but also by heterogeneous physiographical conditions and land use, which makes it ideal for this study. We used 8 years’ worth hydrological data (precipitation, discharge and potential evapotranspiration) to calculate the increments of the water balance and determine the maximum storage capacity and storage deficits. Second, we used the relationship between storage deficit and discharge to estimate total storage at a hypothetical nearly zero flow condition. Third, we compared the pre-hydrological states and event runoff ratios (Q/P) to the catchments’ physiographical conditions in order to link catchment’s sensitivity to storage metrics. We then assessed the responsivity and elasticity to climate and anthropogenic variations – as expressed through the PET/P and AET/P deviations from the Budyko curve and energy limits– for each individual catchment. Finally, we investigated the catchment’s area control on responsivity, elasticity, water yields and Budyko’s elements across our set of 41 nested catchments.</p>

Impact of Increased Vertical Resolution on Medium-Range Forecasts in a Global Atmospheric Model

2019 ◽  
Vol 147 (11) ◽  
pp. 4091-4106 ◽  
Author(s):  
Eunjeong Lee ◽  
Eun-Hee Lee ◽  
In-Jin Choi
Keyword(s):  
Large Scale ◽  
Specific Humidity ◽  
Convective Precipitation ◽  
Tropospheric Temperature ◽  
Vertical Resolution ◽  
Grid Spacing ◽  
Medium Range ◽  
Vertical Grid ◽  
The Impact ◽  
Range Forecasts

Abstract This study aims to investigate the impact of increased vertical resolution on global medium-range forecasts. For this purpose, the dependencies of simulated atmospheric temperature and specific humidity on the lowest model level height and vertical grid spacing are investigated. The reduced first model level increases vertical turbulent mixing by determining a higher planetary boundary layer (PBL) height and associated turbulent diffusivities and velocity scales. This contributes to warming/drying within the PBL and cooling/moistening above the PBL. Resulting dryness near the surface enhances an increase in surface moisture flux from the ocean, which results in the apparent moistening of the troposphere. Consequently, large-scale precipitation increases due to more humid atmospheric conditions, while convective precipitation decreases because of drier conditions near the starting level of convection. Meanwhile, the reduced vertical grid spacing resolves the overshooting layer well in the cumulus convection process, which decreases the detrained moisture at the convective cloud top. This leads to a noticeable downward shift of ice clouds in the upper troposphere, and further contributes to the enhancement of longwave cooling via cloud–radiation processes. In medium-range forecasts, the increased vertical resolution exerts a significant impact on the simulated features of tropospheric temperature and humidity, while changes in the prediction accuracy precipitation are negligible owing to compensation between convective and large-scale precipitation. Finally, the discussion of possible methods to minimize the sensitivities of model’s physics to vertical resolution is presented.

scholarly journals On the Spatial Gradient of Soil Moisture–Precipitation Feedback Strength in the April 2011 Drought in the Southern Great Plains

2017 ◽  
Vol 30 (3) ◽  
pp. 829-848 ◽  
Author(s):  
Hua Su ◽  
Robert E. Dickinson
Keyword(s):  
Soil Moisture ◽  
Great Plains ◽  
Large Scale ◽  
Convective Precipitation ◽  
Spatial Gradient ◽  
Moist Convection ◽  
Southern Great Plains ◽  
Feedback Strength ◽  
Cloud Water Content ◽  
Soil Moisture Anomaly

Abstract The southern Great Plains (SGP) experienced a record-breaking drought in 2011, in which the excessively dry conditions established quickly in spring (i.e., April) and extended into summer. A regional climate model is used (after its evaluation) to simulate this April drought and investigate how a soil moisture anomaly could affect the development of its precipitation deficit. The authors examine how the local thermodynamic structure of the overlying atmosphere contributes to soil moisture feedbacks and how these feedbacks are connected to nonlocal mechanisms. The simulations establish a zonal gradient in the (generally positive) feedback strength [i.e., a significant (negligible) precipitation increase over the eastern (western) SGP] under an SGP-wide wet soil moisture anomaly and spatially similar evapotranspiration (ET) increments. This pattern is dominated by convective precipitation and consistent with spatial gradients in parameters relevant to moist convection, including the precipitable water, the low-level instability and humidity, and the local cloud water content. All these variables are sensitive to a wet soil moisture anomaly, but precipitation responds differently to their changes in different locations. Furthermore, the impacts of the soil moisture anomaly on various large-scale atmospheric fields are related to the spatial structure of feedback strength. Additionally, the weaker feedback over the western SGP occurs in a region of relatively strong subsidence and changes little with a westward expansion of the anomaly area, whereas nonlocal soil moisture impacts—in particular, moisture advection from the west—are important for the stronger feedback over the eastern SGP.

scholarly journals Simulations of deep convection in the Mediterranean area using 3DVAR of conventional and non-conventional data

2005 ◽  
Vol 2 ◽  
pp. 65-71 ◽  
Author(s):  
R. Ferretti ◽  
C. Faccani ◽  
D. Cimini ◽  
F. S. Marzano ◽  
A. Memmo ◽  
...  
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Deep Convection ◽  
Weather Prediction ◽  
Rain Gauge ◽  
Precipitation Forecast ◽  
Variational Assimilation ◽  
First Case ◽  
Surface Data ◽  
The Mediterranean

Abstract. In autumn deep convection in the Mediterranean region is a common phenomenon. The local events characterized by deep convection are still a difficult task even for high resolution numerical weather prediction. Three flood cases, produced by convection either embedded in a large scale system or locally developed, occurring in Italy, are presented. All these case were not correctly forecasted: Sardinia (Cagliari, 13 November 1999); Calabria (Soverato, 7 September 2000) and Sicily (Catania, 16 September 2003). The first case occurred during the Mesoscale Alpine Programme (MAP) campaign, therefore a lot of data are available; for the second one only data from SSM/I and local rain-gauge are available; the third one occurred during the operational experimentation of the TOUGH project. The last one was not well predicted even using the operational assimilation of ground based GPS. To improve the forecast of these cases the assimilation of several data is tested. The variational assimilation performed using 3DVAR of GPS, SSM/I and surface and upper air data is applied to improve the Initial Conditions of the Sicily case. The Sardinia case is improved using either GPS and surface data, whereas for the Soverato case only ZTD is assimilated. The experiments are performed using the MM5 model from Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR); the model is initialized using the new Initial Conditions produced by the variational assimilation of conventional and non conventional data. The results show that the assimilation of the retrieved quantities does produces large improvement in the precipitation forecast. Large sensitivity to the assimilation of surface data and brightness temperature from SSM/I is found.

scholarly journals The Variabilities of Convective Precipitation and Large-scale Precipitation in Southern China under Global Warming

2021 ◽  
Author(s):  
han zhang ◽  
Junhu Zhao ◽  
Bicheng Huang ◽  
Naihui Zang ◽  
Jie Yang ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Large Scale ◽  
Southern China ◽  
Specific Humidity ◽  
Convective Precipitation ◽  
The Past ◽  
The North ◽  
Increasing Trends ◽  
Spatial And Temporal Characteristics ◽  
Linear Trends

Abstract In this paper, the spatial and temporal characteristics of convective precipitation (CP) and large-scale precipitation (LSP) in southern China during 1980-2020 are analyzed using monthly mean precipitation data from MERRA-2. In addition, the possible effects of relative humidity on CP and LSP are explored. The results indicate the following. (1) The LSP dominates the proportion of total precipitation (TP). Both LSP and CP are more prevalent in the south and less prevalent in the north, but there is a difference in the regions of their maximum centers. (2) Significant interannual and seasonal variations are observed in precipitation. TP and LSP tended to be higher than average after the 1990s, while for the CP, a negative trend has dominated the past years with considerable fluctuation. There are obvious increasing trends for TP and LSP, with area-averaged linear trends of 7.0 mm/year and 8.9 mm/year, respectively, while that of CP is -1.9 mm/year. The increasing trends of LSP are mainly contributed by the precipitation of summer and autumn. (3) The variations of LSP are affected by relative humidity in the troposphere, while CP is only influenced by the changes in relative humidity due to air temperature or specific humidity. The trend of relative humidity is -0.32%/decade, mainly due to rising temperature in the troposphere. (4) Changes in specific humidity caused by temperature or specific humidity alone act on large-scale precipitation through both interannual and interdecadal processes, causing large-scale precipitation to increase. And the convective precipitation is mainly affected by the interdecadal processes.

scholarly journals The importance of moisture distribution for the growth and energetics of mid-latitude systems

1999 ◽  
Vol 17 (2) ◽  
pp. 242-256 ◽  
Author(s):  
V. Pavan ◽  
N. Hall ◽  
P. Valdes ◽  
M. Blackburn
Keyword(s):  
Relative Humidity ◽  
Relative Abundance ◽  
Large Scale ◽  
Initial Conditions ◽  
Equation Model ◽  
Life Cycles ◽  
Surface Fluxes ◽  
Moisture Distribution ◽  
Height Distribution ◽  
Moist Convection

Abstract. A primitive equation model is used to study the sensitivity of baroclinic wave life cycles to the initial latitude-height distribution of humidity. Diabatic heating is parametrized only as a consequence of condensation in regions of large-scale ascent. Experiments are performed in which the initial relative humidity is a simple function of model level, and in some cases latitude bands are specified which are initially relatively dry. It is found that the presence of moisture can either increase or decrease the peak eddy kinetic energy of the developing wave, depending on the initial moisture distribution. A relative abundance of moisture at mid-latitudes tends to weaken the wave, while a relative abundance at low latitudes tends to strengthen it. This sensitivity exists because competing processes are at work. These processes are described in terms of energy box diagnostics. The most realistic case lies on the cusp of this sensitivity. Further physical parametrizations are then added, including surface fluxes and upright moist convection. These have the effect of increasing wave amplitude, but the sensitivity to initial conditions of relative humidity remains. Finally, 'control' and 'doubled CO2' life cycles are performed, with initial conditions taken from the time-mean zonal-mean output of equilibrium GCM experiments. The attenuation of the wave resulting from reduced baroclinicity is more pronounced than any effect due to changes in initial moisture.Key words. Meteorology and atmospheric dynamics (climatology; convective processes; synoptic-scale meteorology)

scholarly journals Differences between the Surface Precipitation Estimates from the TRMM Precipitation Radar and Passive Microwave Radiometer Version 7 Products

2014 ◽  
Vol 15 (6) ◽  
pp. 2157-2175 ◽  
Author(s):  
Chuntao Liu ◽  
Edward Zipser
Keyword(s):  
Large Scale ◽  
Microwave Radiometer ◽  
North Indian Ocean ◽  
Passive Microwave ◽  
Convective Precipitation ◽  
Trade Wind ◽  
Precipitation Radar ◽  
Near Surface ◽  
Surface Precipitation ◽  
East Pacific

Abstract With 15 yr of the Tropical Rainfall Measuring Mission (TRMM) observations, the passive microwave radiometers [TRMM Microwave Imager (TMI)] and the precipitation radar (PR) report a close geographical distribution of annual precipitation between 36°S and 36°N. However, large discrepancies between PR and TMI precipitation retrievals are also found over several specific regions, such as central Africa, the Amazon, the tropical east Pacific, and north Indian Ocean. To understand these discrepancies, the PR near-surface and the TMI surface precipitation retrievals are compared at both pixel and precipitation system levels using collocated pixels and a precipitation feature database from 1998 to 2012. Over land, the TMI overestimates precipitation in deep and intense convective systems, but misses significant amounts of warm rainfall in shallow systems. Over the ocean, because of the partial beam filling of large footprints of the lower-frequency sensors, the TMI reports a larger precipitation area than the PR and underestimates the precipitation rate in the convective precipitation region. The TMI tends to overestimate precipitation compared to the PR in a large proportion of shallow systems over the tropical east Pacific and trade wind regions with large-scale descent. The PR tends to overestimate precipitation compared to the TMI in a large proportion of shallow systems over rainy oceans, such as the west Pacific and the Atlantic ITCZ. All these findings imply that there are still large uncertainties in the precipitation climatology over some regions. Further ground validation campaigns are still needed, especially over the ocean.

scholarly journals Linkage among Ice Crystal Microphysics, Mesoscale Dynamics and Cloud and Precipitation Structures Revealed by Collocated Microwave Radiometer and Multi-frequency Radar Observations

2020 ◽  
Author(s):  
Jie Gong ◽  
Xiping Zeng ◽  
Dong L. Wu ◽  
S. Joseph Munchak ◽  
Xiaowen Li ◽  
...  
Keyword(s):  
Deep Convection ◽  
Life Stage ◽  
Microwave Radiometer ◽  
Onset Time ◽  
Radiation Budget ◽  
Convective Precipitation ◽  
Squall Line ◽  
Dual Frequency ◽  
Surface Precipitation ◽  
Stratiform Precipitation

Abstract. Ice clouds and falling snow are ubiquitous globally and play important roles in the Earth's radiation budget and precipitation processes. Ice particle microphysical properties (e.g., size, habit and orientation) are not only influenced by ambient environment's dynamic and thermodynamic conditions, but also intimately connect to the cloud radiative effects and particle fall speeds, which therefore impact up to the future climate projection and down to the details of the surface precipitation (e.g., onset-time, location, type and strength). Our previous work revealed that high-frequency Polarimetric radiance Difference (PD) from passive microwave sensors is a good indicator of the bulk aspect ratio of horizontally oriented ice particles that are often occur inside anvil clouds and/or stratiform precipitations. In this current work, we further investigate the dynamic/thermodynamic mechanisms and cloud/precipitation structures associated with ice-phase microphysics corresponding to different PD signals. In order to do so, collocated CloudSat radar (W-band) and Global Precipitation Measurement Dual-frequency Precipitation Radar (GPM-DPR, Ku/Ka bands) observations as well as European Centre for Medium-Range Weather Forecasts (ECMWF) atmosphere background profiles are grouped according to the magnitude of PD for only stratiform precipitation and/or anvil cloud scenes. We found that horizontally-oriented snow aggregates or large snow particles are likely the major contributor to the high-PD signals at 166 GHz, while low-PD magnitudes can be attributed to small cloud ice, randomly oriented snow aggregates, riming snow or super-cooled water. Further, high (low) PD scenes are found to be associated with stronger (weaker) wind shear and higher (lower) ambient humidity, both of which help promote (prohibit) the growth of frozen particles and the organization of convective systems. An ensemble of squall line cases is studied at the end to demonstrate that the PD asymmetry in the leading and trailing edges of the deep convection line is closely tied to the anvil cloud and stratiform precipitation layers respectively, suggesting the potential usefulness of PD as a proxy of stratiform/convective precipitation flag, as well as a proxy of convection life stage.

scholarly journals Linearization of a Simple Moist Convection Scheme for Large-Scale NWP Models

2005 ◽  
Vol 133 (6) ◽  
pp. 1655-1670 ◽  
Author(s):  
Jean-François Mahfouf
Keyword(s):  
Large Scale ◽  
Temporal Integration ◽  
Preliminary Evaluation ◽  
Moist Convection ◽  
Convection Scheme ◽  
Surface Precipitation ◽  
Cloud Properties ◽  
Convection Schemes ◽  
Linearized Scheme ◽  
Linearization Errors

Abstract A simple Kuo-type convection scheme with an improved closure based on moist enthalpy accession (Kuo symmetric) has been linearized for the tangent-linear (TL) and adjoint (AD) versions of the Global Environmental Multiscale (GEM) model. The nonlinear scheme exhibits a reasonable behavior in terms of heating and moistening rates when evaluated in stand-alone mode over a set of deep convective profiles. A preliminary evaluation of a straightforward linearization in the global TL model has revealed the existence of noise that leads to an unacceptable solution after 12 h of integration. By neglecting several terms in the linearization (detrainment rate and cloud properties), the temporal evolution of humidity analysis increments is improved by including this simplified linearized convection scheme in the TL model. The behavior of the linearized scheme has also been compared favorably to the linearized version of the European Centre for Medium-Range Weather Forecasts (ECMWF) mass-flux convection scheme. When examining the validity of the TL approximation for surface precipitation, it appears that linearization errors are large for both stratiform and convective rainfall (rms errors are about twice the mean absolute perturbed precipitation). These errors are not reduced when considering accumulated rain rates instead of instantaneous quantities. However, the occurrence of “on–off” processes is reduced by a temporal integration of rain. This could make the variational assimilation of accumulated precipitation rates easier. Finally, errors coming from internal nonlinearities are slightly larger than those produced by discontinuities. This confirms the interest for improving the linearity of nonlinear convection schemes for applications in variational contexts.

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