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Research paper thumbnail of Orographic effects on convective precipitation and space-time rainfall variability: preliminary results Orographic effects on convective precipitation and space-time rainfall variability: preliminary results

In the EFFS Project, an attempt has been made to develop a general framework to study the predict... more In the EFFS Project, an attempt has been made to develop a general framework to study the predictability of severe convective rainfall events in the presence of orography. Convective activity is embedded in orographic rainfall and can be thought as the result of several physical mechanisms. Quantifying its variability on selected area and time scales requires choosing the best physical representation of the rainfall variability on these scales. The main goal was (i) to formulate a meaningful set of experiments to compute the oscillation of variance due to convection inside model forecasts in the presence of orography and (ii) to give a statistical measure of it that might be of value in the operational use of atmospheric data. The study has been limited to atmospheric scales that span the atmosphere from 2 to 200 km and has been focused on extreme events with deep convection. Suitable measures of the changing of convection in the presence of orography have been related to the physical properties of the rainfall environment. Preliminary results for the statistical variability of the convective field are presented.

Research paper thumbnail of New perspectives on land–atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis

Research into land–atmosphere coupling within the African Monsoon Multidisciplinary Analysis has ... more Research into land–atmosphere coupling within the African Monsoon Multidisciplinary Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards and time scales of several days. Observational and modelling studies have shown how antecedent rainfall patterns affect new storms in the Sahel. The land feedback operates through various mechanisms, including a direct link to afternoon storm initiation from surface-induced mesoscale circulations, and indirectly via a large-scale moisture transport in the nocturnal monsoon. The results suggest potential for significant improvements in weather forecasting through assimilation of satellite data. Intriguing questions remain about the importance of vegetation memory on seasonal–interannual scales.

Research paper thumbnail of Instabilità barotropica di onde planetarie sulla sfera

Research paper thumbnail of Report on sensitivity of equilibrium states to surface conditions in CRM and SCM

The 3D CRM ARPS and the single column model (SCM) associated to the LMD's GCM (LMDZ4), were u... more The 3D CRM ARPS and the single column model (SCM) associated to the LMD's GCM (LMDZ4), were used to perform idealized experiments on the de-velopment and structural organization of convection in environments at radiative-convective equilibrium given different surface conditions. Three perturbed simula-tions and their relation to the scientific objective of the AMMA project are discussed.

Research paper thumbnail of GEWEX 2014: Trending Now: Water 7th International Scientific Conference on the Global Water and Energy Cycle 14-17 July 2014, The Hague,The Netherlands Topic 21: Topic 21: The coupling of clouds, precipitation, and radiation to the large-scale circulation

The 3D CRM ARPS was used to perform idealized experiments on the development and structural organ... more The 3D CRM ARPS was used to perform idealized experiments on the development and structural organization of convection in environments at radiative-convective equilibrium given different surface conditions. Five simulations lasting more than 100-day starting from previous RCE run are discussed. Different non-homogeneous surface temperatures and initial soundings with different surface parameterization for surface fluxes of heat and moisture were used to simulate the effect of moisture and temperature on the boundary layer dynamics over soil and then on the aggregation of precipitation. Given the symmetry of the model setting, with a horizon- tally uniform radiative cooling with no mean wind and ambient rotation, the not uniform surface temperature is forcing the enthalpy flux, as it can be observed in tropical environments with horizontal patches of temper- ature/humidity. Considering different initial vertical profile imposed to the system a conditionally unstable mode is developin...

Research paper thumbnail of Rochetin, N., Grandpeix, J.-Y. & Cerlini, P. 2009. A study of moist convection sensitivity to surface-boundary-conditions based on CRM and SCM simulations

Research paper thumbnail of Idealized Numerical study of Convective organization

Two distinct non-hydrostatic models, a 2D version of MOLOCH and the 3D ARPS, were used to perform... more Two distinct non-hydrostatic models, a 2D version of MOLOCH and the 3D ARPS, were used to perform idealized experiments on the development and struc- tural organization of convection in environments which either have a high degree of imposed conditional innstability or are near a condition of radiative-convective equilibrium determined by a balancing of sensible/latent heat fluxes at the surface and imposed radiative cooling. Reference cases for both kinds of experiments are shown and their relation to the scientific objective of the project discussed.

Research paper thumbnail of Study of convection in the WAM region using a RC equilibrium approach

A new strategy to modify the R-C equilibrium approach and to adapt it to WAM conditions including... more A new strategy to modify the R-C equilibrium approach and to adapt it to WAM conditions including a forcing provided by the 2D idealized model of Peyrillé and Lafore (2007) has been adopted to start a study of convection in the WAM region (monsoonal area). These simulations have been compared with 3D numerical simulations of an atmosphere in RC equilibrium that can be used as control run for tropical convection. This approach can be used to study different states corresponding to different location of the WAM system.

Research paper thumbnail of An intercomparison between low-frequency variability indices

Tellus A, 1999

Possible connections between spatial patterns, of limited regional extent and identified in telec... more Possible connections between spatial patterns, of limited regional extent and identified in teleconnection patterns and in blocking climatology studies, with hemispheric planetary-wave activity modes defined by the wave amplitude index (WAI) are investigated. The WAI probability density function (PDF) for the northern extratropics winter fields is estimated and the sensitivity of the WAI distribution to the presence of low-frequency variability modes is evaluated by stratifying the available dataset according to the sign of blocking and teleconnection indices. It is found that low-frequency variability modes affect both the mean and the variance of the wave amplitude index. Both the positive phase of the North Atlantic Oscillation (NAO) and the negative phase of the Pacific North American pattern (PNA) are associated with an enhanced frequency of very large amplitude planetary waves. Furthermore, distributions characterised by a maximum corresponding to high WAI values also exhibit a large variance. Negative NAO and positive PNA influence the mean and the variance of WAI PDF in the opposite sense. Similar results are found when the blocking index is considered. WAI PDFs relative to highly blocked months are broader with a secondary maximum corresponding to very high WAI values.

Research paper thumbnail of Numerical Modeling of Atmospheric Water Content and Probability Evaluation. Part II

Procedia Engineering, 2014

Starting from a numerical simulation of tropical atmosphere in radiative convective equilibrium a... more Starting from a numerical simulation of tropical atmosphere in radiative convective equilibrium a perturbation to the surface condition has been applied and the subsequent adjustment of the atmosphere has been analyzed. 3D data have been averaged in space and time using as energy variable to sort them the moist static energy, that is conserved for a moist atmosphere during adiabatic fluid parcel displacements. Since the energy balance of the system corresponds to vertically averaged terms of the MSE differential budget, a entropy derived variable-corresponding to a total thermodynamic energy variable-the θ e equivalent potential temperature, has been analyzed using the vertically block averaged column data sorted by MSE. A close correlation between the energy distribution analyzed as quartile and mean for the θ e and RH vertical profiles is found, highlighting the dynamical link existing between energy and moisture/heat statistical distribution of the system.

Research paper thumbnail of Orographic effects on convective precipitation and space-time rainfall variability: preliminary results

Hydrology and Earth System Sciences, 2005

In the EFFS Project, an attempt has been made to develop a general framework to study the predict... more In the EFFS Project, an attempt has been made to develop a general framework to study the predictability of severe convective rainfall events in the presence of orography. Convective activity is embedded in orographic rainfall and can be thought as the result of several physical mechanisms. Quantifying its variability on selected area and time scales requires choosing the best physical representation of the rainfall variability on these scales. The main goal was (i) to formulate a meaningful set of experiments to compute the oscillation of variance due to convection inside model forecasts in the presence of orography and (ii) to give a statistical measure of it that might be of value in the operational use of atmospheric data. The study has been limited to atmospheric scales that span the atmosphere from 2 to 200 km and has been focused on extreme events with deep convection. Suitable measures of the changing of convection in the presence of orography have been related to the physical properties of the rainfall environment. Preliminary results for the statistical variability of the convective field are presented.

Research paper thumbnail of New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis

Atmospheric Science Letters, 2011

Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards ... more Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards and time scales of several days. Observational and modelling studies have shown how antecedent rainfall patterns affect new storms in the Sahel. The land feedback operates through various mechanisms, including a direct link to afternoon storm initiation from surface-induced mesoscale circulations, and indirectly via a large-scale moisture transport in the nocturnal monsoon. The results suggest potential for significant improvements in weather forecasting through assimilation of satellite data. Intriguing questions remain about the importance of vegetation memory on seasonal-interannual scales.

Research paper thumbnail of New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis

Atmospheric Science Letters, 2011

Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards ... more Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards and time scales of several days. Observational and modelling studies have shown how antecedent rainfall patterns affect new storms in the Sahel. The land feedback operates through various mechanisms, including a direct link to afternoon storm initiation from surface-induced mesoscale circulations, and indirectly via a large-scale moisture transport in the nocturnal monsoon. The results suggest potential for significant improvements in weather forecasting through assimilation of satellite data. Intriguing questions remain about the importance of vegetation memory on seasonal-interannual scales.

Research paper thumbnail of Orographic effects on convective precipitation and space-time rainfall variability: preliminary results Orographic effects on convective precipitation and space-time rainfall variability: preliminary results

In the EFFS Project, an attempt has been made to develop a general framework to study the predict... more In the EFFS Project, an attempt has been made to develop a general framework to study the predictability of severe convective rainfall events in the presence of orography. Convective activity is embedded in orographic rainfall and can be thought as the result of several physical mechanisms. Quantifying its variability on selected area and time scales requires choosing the best physical representation of the rainfall variability on these scales. The main goal was (i) to formulate a meaningful set of experiments to compute the oscillation of variance due to convection inside model forecasts in the presence of orography and (ii) to give a statistical measure of it that might be of value in the operational use of atmospheric data. The study has been limited to atmospheric scales that span the atmosphere from 2 to 200 km and has been focused on extreme events with deep convection. Suitable measures of the changing of convection in the presence of orography have been related to the physical properties of the rainfall environment. Preliminary results for the statistical variability of the convective field are presented.

Research paper thumbnail of New perspectives on land–atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis

Research into land–atmosphere coupling within the African Monsoon Multidisciplinary Analysis has ... more Research into land–atmosphere coupling within the African Monsoon Multidisciplinary Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards and time scales of several days. Observational and modelling studies have shown how antecedent rainfall patterns affect new storms in the Sahel. The land feedback operates through various mechanisms, including a direct link to afternoon storm initiation from surface-induced mesoscale circulations, and indirectly via a large-scale moisture transport in the nocturnal monsoon. The results suggest potential for significant improvements in weather forecasting through assimilation of satellite data. Intriguing questions remain about the importance of vegetation memory on seasonal–interannual scales.

Research paper thumbnail of Instabilità barotropica di onde planetarie sulla sfera

Research paper thumbnail of Report on sensitivity of equilibrium states to surface conditions in CRM and SCM

The 3D CRM ARPS and the single column model (SCM) associated to the LMD's GCM (LMDZ4), were u... more The 3D CRM ARPS and the single column model (SCM) associated to the LMD's GCM (LMDZ4), were used to perform idealized experiments on the de-velopment and structural organization of convection in environments at radiative-convective equilibrium given different surface conditions. Three perturbed simula-tions and their relation to the scientific objective of the AMMA project are discussed.

Research paper thumbnail of GEWEX 2014: Trending Now: Water 7th International Scientific Conference on the Global Water and Energy Cycle 14-17 July 2014, The Hague,The Netherlands Topic 21: Topic 21: The coupling of clouds, precipitation, and radiation to the large-scale circulation

The 3D CRM ARPS was used to perform idealized experiments on the development and structural organ... more The 3D CRM ARPS was used to perform idealized experiments on the development and structural organization of convection in environments at radiative-convective equilibrium given different surface conditions. Five simulations lasting more than 100-day starting from previous RCE run are discussed. Different non-homogeneous surface temperatures and initial soundings with different surface parameterization for surface fluxes of heat and moisture were used to simulate the effect of moisture and temperature on the boundary layer dynamics over soil and then on the aggregation of precipitation. Given the symmetry of the model setting, with a horizon- tally uniform radiative cooling with no mean wind and ambient rotation, the not uniform surface temperature is forcing the enthalpy flux, as it can be observed in tropical environments with horizontal patches of temper- ature/humidity. Considering different initial vertical profile imposed to the system a conditionally unstable mode is developin...

Research paper thumbnail of Rochetin, N., Grandpeix, J.-Y. & Cerlini, P. 2009. A study of moist convection sensitivity to surface-boundary-conditions based on CRM and SCM simulations

Research paper thumbnail of Idealized Numerical study of Convective organization

Two distinct non-hydrostatic models, a 2D version of MOLOCH and the 3D ARPS, were used to perform... more Two distinct non-hydrostatic models, a 2D version of MOLOCH and the 3D ARPS, were used to perform idealized experiments on the development and struc- tural organization of convection in environments which either have a high degree of imposed conditional innstability or are near a condition of radiative-convective equilibrium determined by a balancing of sensible/latent heat fluxes at the surface and imposed radiative cooling. Reference cases for both kinds of experiments are shown and their relation to the scientific objective of the project discussed.

Research paper thumbnail of Study of convection in the WAM region using a RC equilibrium approach

A new strategy to modify the R-C equilibrium approach and to adapt it to WAM conditions including... more A new strategy to modify the R-C equilibrium approach and to adapt it to WAM conditions including a forcing provided by the 2D idealized model of Peyrillé and Lafore (2007) has been adopted to start a study of convection in the WAM region (monsoonal area). These simulations have been compared with 3D numerical simulations of an atmosphere in RC equilibrium that can be used as control run for tropical convection. This approach can be used to study different states corresponding to different location of the WAM system.

Research paper thumbnail of An intercomparison between low-frequency variability indices

Tellus A, 1999

Possible connections between spatial patterns, of limited regional extent and identified in telec... more Possible connections between spatial patterns, of limited regional extent and identified in teleconnection patterns and in blocking climatology studies, with hemispheric planetary-wave activity modes defined by the wave amplitude index (WAI) are investigated. The WAI probability density function (PDF) for the northern extratropics winter fields is estimated and the sensitivity of the WAI distribution to the presence of low-frequency variability modes is evaluated by stratifying the available dataset according to the sign of blocking and teleconnection indices. It is found that low-frequency variability modes affect both the mean and the variance of the wave amplitude index. Both the positive phase of the North Atlantic Oscillation (NAO) and the negative phase of the Pacific North American pattern (PNA) are associated with an enhanced frequency of very large amplitude planetary waves. Furthermore, distributions characterised by a maximum corresponding to high WAI values also exhibit a large variance. Negative NAO and positive PNA influence the mean and the variance of WAI PDF in the opposite sense. Similar results are found when the blocking index is considered. WAI PDFs relative to highly blocked months are broader with a secondary maximum corresponding to very high WAI values.

Research paper thumbnail of Numerical Modeling of Atmospheric Water Content and Probability Evaluation. Part II

Procedia Engineering, 2014

Starting from a numerical simulation of tropical atmosphere in radiative convective equilibrium a... more Starting from a numerical simulation of tropical atmosphere in radiative convective equilibrium a perturbation to the surface condition has been applied and the subsequent adjustment of the atmosphere has been analyzed. 3D data have been averaged in space and time using as energy variable to sort them the moist static energy, that is conserved for a moist atmosphere during adiabatic fluid parcel displacements. Since the energy balance of the system corresponds to vertically averaged terms of the MSE differential budget, a entropy derived variable-corresponding to a total thermodynamic energy variable-the θ e equivalent potential temperature, has been analyzed using the vertically block averaged column data sorted by MSE. A close correlation between the energy distribution analyzed as quartile and mean for the θ e and RH vertical profiles is found, highlighting the dynamical link existing between energy and moisture/heat statistical distribution of the system.

Research paper thumbnail of Orographic effects on convective precipitation and space-time rainfall variability: preliminary results

Hydrology and Earth System Sciences, 2005

In the EFFS Project, an attempt has been made to develop a general framework to study the predict... more In the EFFS Project, an attempt has been made to develop a general framework to study the predictability of severe convective rainfall events in the presence of orography. Convective activity is embedded in orographic rainfall and can be thought as the result of several physical mechanisms. Quantifying its variability on selected area and time scales requires choosing the best physical representation of the rainfall variability on these scales. The main goal was (i) to formulate a meaningful set of experiments to compute the oscillation of variance due to convection inside model forecasts in the presence of orography and (ii) to give a statistical measure of it that might be of value in the operational use of atmospheric data. The study has been limited to atmospheric scales that span the atmosphere from 2 to 200 km and has been focused on extreme events with deep convection. Suitable measures of the changing of convection in the presence of orography have been related to the physical properties of the rainfall environment. Preliminary results for the statistical variability of the convective field are presented.

Research paper thumbnail of New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis

Atmospheric Science Letters, 2011

Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards ... more Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards and time scales of several days. Observational and modelling studies have shown how antecedent rainfall patterns affect new storms in the Sahel. The land feedback operates through various mechanisms, including a direct link to afternoon storm initiation from surface-induced mesoscale circulations, and indirectly via a large-scale moisture transport in the nocturnal monsoon. The results suggest potential for significant improvements in weather forecasting through assimilation of satellite data. Intriguing questions remain about the importance of vegetation memory on seasonal-interannual scales.

Research paper thumbnail of New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis

Atmospheric Science Letters, 2011

Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards ... more Analysis has highlighted the atmospheric impact of soil moisture on space scales of 5 km upwards and time scales of several days. Observational and modelling studies have shown how antecedent rainfall patterns affect new storms in the Sahel. The land feedback operates through various mechanisms, including a direct link to afternoon storm initiation from surface-induced mesoscale circulations, and indirectly via a large-scale moisture transport in the nocturnal monsoon. The results suggest potential for significant improvements in weather forecasting through assimilation of satellite data. Intriguing questions remain about the importance of vegetation memory on seasonal-interannual scales.