Interaction of multiple oscillations of different time scales may result in severe weather events... more Interaction of multiple oscillations of different time scales may result in severe weather events. The presence of orography can modulate the intensity of these events even further. Kerala witnessed one such heavy rainfall event in August, 2018, claiming 483 lives and damages worth INR 200 billion. This study focuses on the peak rainfall duration (13–17 August) when the departure from normal was 42%. Segregating moisture transport into its mean and perturbation terms show that an anomalous moisture channel over the Arabian Sea supplied continuous moisture to the Western Ghats (WG), whereas anomalous wind due to a monsoon depression advected moisture towards the southern peninsula. It is evident in the form of Moisture Flux Convergence (MFC) towers traversing along the Eastern Ghats before merging with the semi-permanent MFC feature over the WG. The presence of positive quasi bi-weekly oscillations and of Intra Seasonal Oscillations (ISO) aggravated the event as they complemented the...
The present study is aimed to investigate sub-surface ocean processes and their contribution to t... more The present study is aimed to investigate sub-surface ocean processes and their contribution to the intensification of a tropical cyclone (TC) from a coupled-modeling perspective. The Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) model was employed to simulate TC Phailin, which originated over the Bay of Bengal and made landfall on the eastern coast of India in October 2013. Three sub-surface ocean condition datasets—viz., (a) the European Centre for Medium-Range Weather Forecast (ECMWF) Ocean Reanalysis, (b) the Climate Forecast System Version 2 (CFSV2) Operational Analysis, and (c) the Hybrid Coordinate Ocean Model (HYCOM) Reanalysis datasets—were used for the initial and boundary conditions for the oceanic component of the coupled model in three different simulations of TC Phailin. All the simulations showed a delay in intensification compared to the observation, and ECMWF simulated the most intensified TC. CFSV2 simulated a deeper mixed layer (ML) and higher mixing, ...
In this study, a comprehensive investigation is carried out to examine the sensitivity of troposp... more In this study, a comprehensive investigation is carried out to examine the sensitivity of tropospheric relative humidity (RH) on monsoon depressions (MDs) under a changing climate regime through surrogate climate change approach over the Indian region. Composite analysis of four MDs show a persistent warming (RH2+) and cooling (RH2−) throughout the troposphere in the sensitivity experiments. In-depth analysis of a MD over the Arabian Sea (AS) exhibits sustained warming for RH2+, which is accredited to 2.6% increase in stratiform clouds accounting for 13% increment in heating, whereas 5% increment in convective clouds hardly contribute to total heating. Frozen hydrometeors (graupel and snow) are speculated to be the major contributors to this heating. Stratiform clouds showed greater sensitivity to RH perturbations in the lower troposphere (1000–750 hPa), albeit very less sensitivity for convective clouds, both in the lower and mid-troposphere (700–500 hPa). Precipitation is enhanced...
A correction to this article has been published and is linked from the HTML and PDF versions of t... more A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.
In this study, the impact of different land initial conditions on the simulation of thunderstorms... more In this study, the impact of different land initial conditions on the simulation of thunderstorms and monsoon depressions is investigated using the Weather Research and Forecasting (WRF) model. A control run (CNTL) and a simulation with an improved land state (soil moisture and temperature) using the High Resolution Land Data Assimilation System (HRLDAS, experiment name: EHRLDAS) are compared for three different rainfall cases in order to examine the robustness of the assimilation system. The study comprises two thunderstorm cases (one in the pre-monsoon and one during the monsoon) and one monsoon depression case that occurred during the Interaction of Convective Organisation, Atmosphere, Surface and Sea (INCOMPASS) field campaign of the 2016 Indian monsoon. EHRLDAS is shown to yield improvements in the representation of location-specific rainfall, particularly over land. Further, it is found that surface fluxes as well as convective indices are better captured for the pre-monsoon t...
The state of Odisha is situated on the eastern coast of India and is highly vulnerable to massive... more The state of Odisha is situated on the eastern coast of India and is highly vulnerable to massive convective activity in the pre-monsoon season (PM), i.e., from March to May; however, there is a scarcity of studies in this context using long-term datasets. Therefore, an in-depth investigation of the variability in convective events and associated rainfall during PM over the state of Odisha has been carried out for the period 2009–2018 using the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation reanalysis (ERA5) datasets. The convective events (severe and moderate) identified using two sets of threshold values of three different convective indices, i.e., convective available potential energy (CAPE), the K Index, and the Total Totals Index, show an increasing trend in recent years, with South Coastal Odisha (SCO) and North Coastal Odisha (NCO) showing the highest increase. Subsequently, the spatial distribution of rainfall suggests that the maximum convective precipitation (CP) is experienced over NCO and adjacent eastern districts of North Interior Odisha (NIO). The spatial distribution of the 2 m temperature suggests that there exists a strong temperature gradient between the western and eastern portions of the state. However, the gradient weakens for the years associated with the anomalous distribution of CP. The distinct tropospheric temperature difference between the lower levels (LL) and upper levels (UL) clearly suggests that the warming (cooling) of LL is associated with high (low) CP over the region. This is further established by the coherent signature of specific humidity. The frozen hydrometeors (cloud ice and snow) are the major facilitators for the occurrence of CP over the study region. The moisture transport (MT) is associated primarily with the anomalous distribution of spatial rainfall. The years with suppressed convective activity have a distinct signature of a negative MT anomaly along with anomalous north-easterly winds (as against the typical south-westerly flow). It is also demonstrated that the anomalous MT scenario is highly modulated by the land–sea temperature contrast over the region.
This study characterizes different rainfall types using surface-based instruments (i.e. micro rai... more This study characterizes different rainfall types using surface-based instruments (i.e. micro rain radar and laser precipitation monitor) installed at the Indian Institute of Technology Bhubaneswar Jatani, Odisha, India. A total of twelve rainfall cases including four from each season, i.e. pre-monsoon, monsoon and post-monsoon, are considered. The segregation of rainfall is carried out using radar reflectivity and rainfall intensity. In general, initial rainfall is dominantly convective and followed by a stratiform type. Two distinct maxima of radar reflectivity are noted at 3 and 5 km, suggesting the presence of high liquid water content and a melting band. The presence of liquid water content suggests occurrence of a warm rain process with shallow, intense convective cores. Results indicate a higher drop number density below 2 km with smaller size drops for convective rainfall and vice versa for the stratiform rainfall. Furthermore, Z – R relationships are computed for all the cases using a linear regression method, and the results suggest that the stratiform rainfall shows a higher slope parameter and lower intercept parameter as compared to convective rainfall. The distribution of drop number density shows a mono-modal and bimodal pattern for convective and stratiform rainfall, respectively.
Abstract Monsoon depressions (MDs) constitute a large fraction of the total rainfall during the I... more Abstract Monsoon depressions (MDs) constitute a large fraction of the total rainfall during the Indian summer monsoon season. In this study, the impact of high-resolution land state is addressed by assessing the evolution of inland moving depressions formed over the Bay of Bengal using a mesoscale modeling system. Improved land state is generated using High Resolution Land Data Assimilation System employing Noah-MP land-surface model. Verification of soil moisture using Soil Moisture and Ocean Salinity (SMOS) and soil temperature using tower observations demonstrate promising results. Incorporating high-resolution land state yielded least root mean squared errors with higher correlation coefficient in the surface and mid tropospheric parameters. Rainfall forecasts reveal that simulations are spatially and quantitatively in accordance with observations and provide better skill scores. The improved land surface characteristics have brought about the realistic evolution of surface, mid-tropospheric parameters, vorticity and moist static energy that facilitates the accurate MDs dynamics in the model. Composite moisture budget analysis reveals that the surface evaporation is negligible compared to moisture flux convergence of water vapor, which supplies moisture into the MDs over land. The temporal relationship between rainfall and moisture convergence show high correlation, suggesting a realistic representation of land state help restructure the moisture inflow into the system through rainfall-moisture convergence feedback.
Interaction of multiple oscillations of different time scales may result in severe weather events... more Interaction of multiple oscillations of different time scales may result in severe weather events. The presence of orography can modulate the intensity of these events even further. Kerala witnessed one such heavy rainfall event in August, 2018, claiming 483 lives and damages worth INR 200 billion. This study focuses on the peak rainfall duration (13–17 August) when the departure from normal was 42%. Segregating moisture transport into its mean and perturbation terms show that an anomalous moisture channel over the Arabian Sea supplied continuous moisture to the Western Ghats (WG), whereas anomalous wind due to a monsoon depression advected moisture towards the southern peninsula. It is evident in the form of Moisture Flux Convergence (MFC) towers traversing along the Eastern Ghats before merging with the semi-permanent MFC feature over the WG. The presence of positive quasi bi-weekly oscillations and of Intra Seasonal Oscillations (ISO) aggravated the event as they complemented the...
The present study is aimed to investigate sub-surface ocean processes and their contribution to t... more The present study is aimed to investigate sub-surface ocean processes and their contribution to the intensification of a tropical cyclone (TC) from a coupled-modeling perspective. The Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) model was employed to simulate TC Phailin, which originated over the Bay of Bengal and made landfall on the eastern coast of India in October 2013. Three sub-surface ocean condition datasets—viz., (a) the European Centre for Medium-Range Weather Forecast (ECMWF) Ocean Reanalysis, (b) the Climate Forecast System Version 2 (CFSV2) Operational Analysis, and (c) the Hybrid Coordinate Ocean Model (HYCOM) Reanalysis datasets—were used for the initial and boundary conditions for the oceanic component of the coupled model in three different simulations of TC Phailin. All the simulations showed a delay in intensification compared to the observation, and ECMWF simulated the most intensified TC. CFSV2 simulated a deeper mixed layer (ML) and higher mixing, ...
In this study, a comprehensive investigation is carried out to examine the sensitivity of troposp... more In this study, a comprehensive investigation is carried out to examine the sensitivity of tropospheric relative humidity (RH) on monsoon depressions (MDs) under a changing climate regime through surrogate climate change approach over the Indian region. Composite analysis of four MDs show a persistent warming (RH2+) and cooling (RH2−) throughout the troposphere in the sensitivity experiments. In-depth analysis of a MD over the Arabian Sea (AS) exhibits sustained warming for RH2+, which is accredited to 2.6% increase in stratiform clouds accounting for 13% increment in heating, whereas 5% increment in convective clouds hardly contribute to total heating. Frozen hydrometeors (graupel and snow) are speculated to be the major contributors to this heating. Stratiform clouds showed greater sensitivity to RH perturbations in the lower troposphere (1000–750 hPa), albeit very less sensitivity for convective clouds, both in the lower and mid-troposphere (700–500 hPa). Precipitation is enhanced...
A correction to this article has been published and is linked from the HTML and PDF versions of t... more A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.
In this study, the impact of different land initial conditions on the simulation of thunderstorms... more In this study, the impact of different land initial conditions on the simulation of thunderstorms and monsoon depressions is investigated using the Weather Research and Forecasting (WRF) model. A control run (CNTL) and a simulation with an improved land state (soil moisture and temperature) using the High Resolution Land Data Assimilation System (HRLDAS, experiment name: EHRLDAS) are compared for three different rainfall cases in order to examine the robustness of the assimilation system. The study comprises two thunderstorm cases (one in the pre-monsoon and one during the monsoon) and one monsoon depression case that occurred during the Interaction of Convective Organisation, Atmosphere, Surface and Sea (INCOMPASS) field campaign of the 2016 Indian monsoon. EHRLDAS is shown to yield improvements in the representation of location-specific rainfall, particularly over land. Further, it is found that surface fluxes as well as convective indices are better captured for the pre-monsoon t...
The state of Odisha is situated on the eastern coast of India and is highly vulnerable to massive... more The state of Odisha is situated on the eastern coast of India and is highly vulnerable to massive convective activity in the pre-monsoon season (PM), i.e., from March to May; however, there is a scarcity of studies in this context using long-term datasets. Therefore, an in-depth investigation of the variability in convective events and associated rainfall during PM over the state of Odisha has been carried out for the period 2009–2018 using the European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation reanalysis (ERA5) datasets. The convective events (severe and moderate) identified using two sets of threshold values of three different convective indices, i.e., convective available potential energy (CAPE), the K Index, and the Total Totals Index, show an increasing trend in recent years, with South Coastal Odisha (SCO) and North Coastal Odisha (NCO) showing the highest increase. Subsequently, the spatial distribution of rainfall suggests that the maximum convective precipitation (CP) is experienced over NCO and adjacent eastern districts of North Interior Odisha (NIO). The spatial distribution of the 2 m temperature suggests that there exists a strong temperature gradient between the western and eastern portions of the state. However, the gradient weakens for the years associated with the anomalous distribution of CP. The distinct tropospheric temperature difference between the lower levels (LL) and upper levels (UL) clearly suggests that the warming (cooling) of LL is associated with high (low) CP over the region. This is further established by the coherent signature of specific humidity. The frozen hydrometeors (cloud ice and snow) are the major facilitators for the occurrence of CP over the study region. The moisture transport (MT) is associated primarily with the anomalous distribution of spatial rainfall. The years with suppressed convective activity have a distinct signature of a negative MT anomaly along with anomalous north-easterly winds (as against the typical south-westerly flow). It is also demonstrated that the anomalous MT scenario is highly modulated by the land–sea temperature contrast over the region.
This study characterizes different rainfall types using surface-based instruments (i.e. micro rai... more This study characterizes different rainfall types using surface-based instruments (i.e. micro rain radar and laser precipitation monitor) installed at the Indian Institute of Technology Bhubaneswar Jatani, Odisha, India. A total of twelve rainfall cases including four from each season, i.e. pre-monsoon, monsoon and post-monsoon, are considered. The segregation of rainfall is carried out using radar reflectivity and rainfall intensity. In general, initial rainfall is dominantly convective and followed by a stratiform type. Two distinct maxima of radar reflectivity are noted at 3 and 5 km, suggesting the presence of high liquid water content and a melting band. The presence of liquid water content suggests occurrence of a warm rain process with shallow, intense convective cores. Results indicate a higher drop number density below 2 km with smaller size drops for convective rainfall and vice versa for the stratiform rainfall. Furthermore, Z – R relationships are computed for all the cases using a linear regression method, and the results suggest that the stratiform rainfall shows a higher slope parameter and lower intercept parameter as compared to convective rainfall. The distribution of drop number density shows a mono-modal and bimodal pattern for convective and stratiform rainfall, respectively.
Abstract Monsoon depressions (MDs) constitute a large fraction of the total rainfall during the I... more Abstract Monsoon depressions (MDs) constitute a large fraction of the total rainfall during the Indian summer monsoon season. In this study, the impact of high-resolution land state is addressed by assessing the evolution of inland moving depressions formed over the Bay of Bengal using a mesoscale modeling system. Improved land state is generated using High Resolution Land Data Assimilation System employing Noah-MP land-surface model. Verification of soil moisture using Soil Moisture and Ocean Salinity (SMOS) and soil temperature using tower observations demonstrate promising results. Incorporating high-resolution land state yielded least root mean squared errors with higher correlation coefficient in the surface and mid tropospheric parameters. Rainfall forecasts reveal that simulations are spatially and quantitatively in accordance with observations and provide better skill scores. The improved land surface characteristics have brought about the realistic evolution of surface, mid-tropospheric parameters, vorticity and moist static energy that facilitates the accurate MDs dynamics in the model. Composite moisture budget analysis reveals that the surface evaporation is negligible compared to moisture flux convergence of water vapor, which supplies moisture into the MDs over land. The temporal relationship between rainfall and moisture convergence show high correlation, suggesting a realistic representation of land state help restructure the moisture inflow into the system through rainfall-moisture convergence feedback.
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