Vickal Kumar - Academia.edu (original) (raw)

Papers by Vickal Kumar

Research paper thumbnail of Optimizing the probability of flying in high ice water content conditions in the Tropics using a regional-scale climatology of convective cell properties

Research paper thumbnail of Retrievals Of Vertical Motion in Convective Precipitating Systems: an ARM Perspective

ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as ac... more ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as accretion rates, species transport (water vapor, aerosols) and radiative properties of detrained cloud anvils, and being strongly influenced my many scales of dynamical forcing, latent heat feedbacks and entrainment. Due to this, statistical properties of vertical motion can act as an observational target for fine scale (eg LES, CRM) models. Determining the veracity of processes in such models is vital as these are commonly used to asses processes in Single column and global models. However retrievals of vertical motions in these systems is complicated by many factors including sampling, the veracity of constraints and boundary and initial conditions used in the retrieval. Therefore a multi-scale approach is needed, using a mix of independent measurements and retrieval techniques to build an understanding of the vertical velocity spectrum in these systems. This presentation will cover work across the ARM facility including retrievals from the Darwin Tropical West Pacific (Australia) and the Oklahoma, Southern Great Plains (USA) site. By initially focusing on Intensive Observational Periods such as TWP-ICE and MC3E retrieval efforts can dovetail with model intercomparison projects and ongoing work in parameterization and model development. In addition to ongoing work paths towards building single radar based retrievals leveraging microphysical insight from polarimetric radars will be discussed.

Research paper thumbnail of Mass-Flux Characteristics of Tropical Cumulus Clouds from Wind Profiler Observations at Darwin, Australia

Http Dx Doi Org 10 1175 Jas D 14 0259 1, May 1, 2015

Research paper thumbnail of Comparison of Two Convective/Stratiform Precipitation Classification Techniques: Radar Reflectivity Texture versus Drop Size Distribution–Based Approach

Journal of Atmospheric and Oceanic Technology, Dec 1, 2013

Research paper thumbnail of The estimation of convective mass flux from radar reflectivities

Journal of Applied Meteorology and Climatology, 2016

Research paper thumbnail of Relationships between the large-scale atmosphere and the small-scale convective state for Darwin, Australia

Journal of Geophysical Research: Atmospheres, 2013

Research paper thumbnail of Representing convection in models -How stochastic does it need to be?

Research paper thumbnail of On the occurrence of equatorial F-region irregularities during solar minimum using radio occultation measurements

Journal of Geophysical Research: Space Physics, 2013

Research paper thumbnail of Surface fair-weather potential gradient measurements from a small tropical island station Suva, Fiji

Earth, Planets and Space, 2009

Research paper thumbnail of Mass-flux characteristics of tropical cumulus clouds from wind profiler observations at Darwin, Australia

Journal of the Atmospheric Sciences, 2015

Research paper thumbnail of The four cumulus cloud modes and their progression during rainfall events: A C-band polarimetric radar perspective

Journal of Geophysical Research: Atmospheres, 2013

Research paper thumbnail of A regional forecast model evaluation of statistical rainfall properties using CPOL radar observations in different precipitation regimes over Darwin, Australia

Quarterly Journal of the Royal Meteorological Society, 2015

Research paper thumbnail of Retrievals Of Vertical Motion in Convective Precipitating Systems: an ARM Perspective

ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as ac... more ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as accretion rates, species transport (water vapor, aerosols) and radiative properties of detrained cloud anvils, and being strongly influenced my many scales of dynamical forcing, latent heat feedbacks and entrainment. Due to this, statistical properties of vertical motion can act as an observational target for fine scale (eg LES, CRM) models. Determining the veracity of processes in such models is vital as these are commonly used to asses processes in Single column and global models. However retrievals of vertical motions in these systems is complicated by many factors including sampling, the veracity of constraints and boundary and initial conditions used in the retrieval. Therefore a multi-scale approach is needed, using a mix of independent measurements and retrieval techniques to build an understanding of the vertical velocity spectrum in these systems. This presentation will cover work across the ARM facility including retrievals from the Darwin Tropical West Pacific (Australia) and the Oklahoma, Southern Great Plains (USA) site. By initially focusing on Intensive Observational Periods such as TWP-ICE and MC3E retrieval efforts can dovetail with model intercomparison projects and ongoing work in parameterization and model development. In addition to ongoing work paths towards building single radar based retrievals leveraging microphysical insight from polarimetric radars will be discussed.

Research paper thumbnail of Preliminary findings of the effect of some atmospheric parameters on Ku-band satellite link

Research paper thumbnail of Preliminary findings of surface fair-weather electric field trends over small tropical island station, Suva, Fiji

The South Pacific Journal of Natural Science, 2007

Research paper thumbnail of On the Effects of Large-Scale Environment and Surface Types on Convective Cloud Characteristics over Darwin, Australia

Monthly Weather Review, 2013

Research paper thumbnail of Statistics of Drop Size Distribution Parameters and Rain Rates for Stratiform and Convective Precipitation during the North Australian Wet Season

Monthly Weather Review, 2013

Research paper thumbnail of On the Atmospheric Regulation of the Growth of Moderate to Deep Cumulonimbus in a Tropical Environment

Journal of the Atmospheric Sciences, 2014

ABSTRACT Some cumulus clouds with tops between 3 and 7 km (Cu3km-7km) remain in this height regio... more ABSTRACT Some cumulus clouds with tops between 3 and 7 km (Cu3km-7km) remain in this height region throughout their lifetime (congestus) while others develop into deeper clouds (cumulonimbus). This study describes two techniques to identify the congestus and cumulonimbus cloud types using data from scanning weather radar and identifies the atmospheric conditions that regulate these two modes. A two-wet-season cumulus cloud database of the Darwin C-band polarimetric radar is analyzed and the two modes are identified by examining the 0-dBZ cloud-top height (CTH) of the Cu3km-7km cells over a sequence of radar scans. It is found that similar to 26% of the classified Cu3km-7km population grow into cumulonimbus clouds. The cumulonimbus cells exhibit reflectivities, rain rates, and drop sizes larger than the congestus cells. The occurrence frequency of cumulonimbus cells peak in the afternoon at similar to 1500 local timea few hours after the peak in congestus cells. The analysis of Darwin International Airport radiosonde profiles associated with the two types of cells shows no noticeable difference in the thermal stability rates, but a significant difference in midtropospheric (5-10 km) relative humidity. Moister conditions are found in the hours preceding the cumulonimbus cells when compared with the congestus cells. Using a moisture budget dataset derived for the Darwin region, it is shown that the existence of cumulonimbus cells, and hence deep convection, is mainly determined by the presence of the midtroposphere large-scale upward motion and not merely by the presence of congestus clouds prior to deep convection. This contradicts the thermodynamic viewpoint that the midtroposphere moistening prior to deep convection is solely due to the preceding cumulus congestus cells.

Research paper thumbnail of On the temporal evolution of midlatitude F region disturbance drifts

Journal of Geophysical Research, 2010

Superposed Epoch Analysis (SEA) is used to examine a 5-year (1999 to 2003) database of Digisonde ... more Superposed Epoch Analysis (SEA) is used to examine a 5-year (1999 to 2003) database of Digisonde drift measurements made at Bundoora (145.1°E, 37.7°S geographic, 49°S magnetic), Australia, to determine the temporal evolution of midlatitude F region electric fields associated with the magnetospheric (lifetimes of about an hour) and ionospheric disturbance (lifetimes of a few to several hours) dynamos. The magnetospheric

Research paper thumbnail of Invariance of Accumulation Time Factor of Ku-Band Signals in the Tropics

Journal of Electromagnetic Waves and Applications, 2005

ABSTRACT Simultaneous measurements of Ku-band attenuation and rain-rate give A 0.01 and R 0.01 as... more ABSTRACT Simultaneous measurements of Ku-band attenuation and rain-rate give A 0.01 and R 0.01 as 9.7 dB and 54 mm/hr respectively, Unlike the monotonous variation predicted by the ITU-R model, breakpoints were observed in both the rain-rate and Ku-band attenuation exceedances. Similar observations were reported from other stations in the tropics. The accumulation time factor measured at the breakpoints remained almost a constant in these stations. Using this it is predicted that for stations with high elevation angle receivers, at breakpoint rain-rates, one rain-cell intercepts the propagation path of the signal. It is estimated that, in the tropics, the diameter of a rain-cell is 1.5 km when the rain-rate begin to saturate.

Research paper thumbnail of Optimizing the probability of flying in high ice water content conditions in the Tropics using a regional-scale climatology of convective cell properties

Research paper thumbnail of Retrievals Of Vertical Motion in Convective Precipitating Systems: an ARM Perspective

ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as ac... more ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as accretion rates, species transport (water vapor, aerosols) and radiative properties of detrained cloud anvils, and being strongly influenced my many scales of dynamical forcing, latent heat feedbacks and entrainment. Due to this, statistical properties of vertical motion can act as an observational target for fine scale (eg LES, CRM) models. Determining the veracity of processes in such models is vital as these are commonly used to asses processes in Single column and global models. However retrievals of vertical motions in these systems is complicated by many factors including sampling, the veracity of constraints and boundary and initial conditions used in the retrieval. Therefore a multi-scale approach is needed, using a mix of independent measurements and retrieval techniques to build an understanding of the vertical velocity spectrum in these systems. This presentation will cover work across the ARM facility including retrievals from the Darwin Tropical West Pacific (Australia) and the Oklahoma, Southern Great Plains (USA) site. By initially focusing on Intensive Observational Periods such as TWP-ICE and MC3E retrieval efforts can dovetail with model intercomparison projects and ongoing work in parameterization and model development. In addition to ongoing work paths towards building single radar based retrievals leveraging microphysical insight from polarimetric radars will be discussed.

Research paper thumbnail of Mass-Flux Characteristics of Tropical Cumulus Clouds from Wind Profiler Observations at Darwin, Australia

Http Dx Doi Org 10 1175 Jas D 14 0259 1, May 1, 2015

Research paper thumbnail of Comparison of Two Convective/Stratiform Precipitation Classification Techniques: Radar Reflectivity Texture versus Drop Size Distribution–Based Approach

Journal of Atmospheric and Oceanic Technology, Dec 1, 2013

Research paper thumbnail of The estimation of convective mass flux from radar reflectivities

Journal of Applied Meteorology and Climatology, 2016

Research paper thumbnail of Relationships between the large-scale atmosphere and the small-scale convective state for Darwin, Australia

Journal of Geophysical Research: Atmospheres, 2013

Research paper thumbnail of Representing convection in models -How stochastic does it need to be?

Research paper thumbnail of On the occurrence of equatorial F-region irregularities during solar minimum using radio occultation measurements

Journal of Geophysical Research: Space Physics, 2013

Research paper thumbnail of Surface fair-weather potential gradient measurements from a small tropical island station Suva, Fiji

Earth, Planets and Space, 2009

Research paper thumbnail of Mass-flux characteristics of tropical cumulus clouds from wind profiler observations at Darwin, Australia

Journal of the Atmospheric Sciences, 2015

Research paper thumbnail of The four cumulus cloud modes and their progression during rainfall events: A C-band polarimetric radar perspective

Journal of Geophysical Research: Atmospheres, 2013

Research paper thumbnail of A regional forecast model evaluation of statistical rainfall properties using CPOL radar observations in different precipitation regimes over Darwin, Australia

Quarterly Journal of the Royal Meteorological Society, 2015

Research paper thumbnail of Retrievals Of Vertical Motion in Convective Precipitating Systems: an ARM Perspective

ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as ac... more ABSTRACT Vertical motions in the atmosphere link many processes, controlling processes such as accretion rates, species transport (water vapor, aerosols) and radiative properties of detrained cloud anvils, and being strongly influenced my many scales of dynamical forcing, latent heat feedbacks and entrainment. Due to this, statistical properties of vertical motion can act as an observational target for fine scale (eg LES, CRM) models. Determining the veracity of processes in such models is vital as these are commonly used to asses processes in Single column and global models. However retrievals of vertical motions in these systems is complicated by many factors including sampling, the veracity of constraints and boundary and initial conditions used in the retrieval. Therefore a multi-scale approach is needed, using a mix of independent measurements and retrieval techniques to build an understanding of the vertical velocity spectrum in these systems. This presentation will cover work across the ARM facility including retrievals from the Darwin Tropical West Pacific (Australia) and the Oklahoma, Southern Great Plains (USA) site. By initially focusing on Intensive Observational Periods such as TWP-ICE and MC3E retrieval efforts can dovetail with model intercomparison projects and ongoing work in parameterization and model development. In addition to ongoing work paths towards building single radar based retrievals leveraging microphysical insight from polarimetric radars will be discussed.

Research paper thumbnail of Preliminary findings of the effect of some atmospheric parameters on Ku-band satellite link

Research paper thumbnail of Preliminary findings of surface fair-weather electric field trends over small tropical island station, Suva, Fiji

The South Pacific Journal of Natural Science, 2007

Research paper thumbnail of On the Effects of Large-Scale Environment and Surface Types on Convective Cloud Characteristics over Darwin, Australia

Monthly Weather Review, 2013

Research paper thumbnail of Statistics of Drop Size Distribution Parameters and Rain Rates for Stratiform and Convective Precipitation during the North Australian Wet Season

Monthly Weather Review, 2013

Research paper thumbnail of On the Atmospheric Regulation of the Growth of Moderate to Deep Cumulonimbus in a Tropical Environment

Journal of the Atmospheric Sciences, 2014

ABSTRACT Some cumulus clouds with tops between 3 and 7 km (Cu3km-7km) remain in this height regio... more ABSTRACT Some cumulus clouds with tops between 3 and 7 km (Cu3km-7km) remain in this height region throughout their lifetime (congestus) while others develop into deeper clouds (cumulonimbus). This study describes two techniques to identify the congestus and cumulonimbus cloud types using data from scanning weather radar and identifies the atmospheric conditions that regulate these two modes. A two-wet-season cumulus cloud database of the Darwin C-band polarimetric radar is analyzed and the two modes are identified by examining the 0-dBZ cloud-top height (CTH) of the Cu3km-7km cells over a sequence of radar scans. It is found that similar to 26% of the classified Cu3km-7km population grow into cumulonimbus clouds. The cumulonimbus cells exhibit reflectivities, rain rates, and drop sizes larger than the congestus cells. The occurrence frequency of cumulonimbus cells peak in the afternoon at similar to 1500 local timea few hours after the peak in congestus cells. The analysis of Darwin International Airport radiosonde profiles associated with the two types of cells shows no noticeable difference in the thermal stability rates, but a significant difference in midtropospheric (5-10 km) relative humidity. Moister conditions are found in the hours preceding the cumulonimbus cells when compared with the congestus cells. Using a moisture budget dataset derived for the Darwin region, it is shown that the existence of cumulonimbus cells, and hence deep convection, is mainly determined by the presence of the midtroposphere large-scale upward motion and not merely by the presence of congestus clouds prior to deep convection. This contradicts the thermodynamic viewpoint that the midtroposphere moistening prior to deep convection is solely due to the preceding cumulus congestus cells.

Research paper thumbnail of On the temporal evolution of midlatitude F region disturbance drifts

Journal of Geophysical Research, 2010

Superposed Epoch Analysis (SEA) is used to examine a 5-year (1999 to 2003) database of Digisonde ... more Superposed Epoch Analysis (SEA) is used to examine a 5-year (1999 to 2003) database of Digisonde drift measurements made at Bundoora (145.1°E, 37.7°S geographic, 49°S magnetic), Australia, to determine the temporal evolution of midlatitude F region electric fields associated with the magnetospheric (lifetimes of about an hour) and ionospheric disturbance (lifetimes of a few to several hours) dynamos. The magnetospheric

Research paper thumbnail of Invariance of Accumulation Time Factor of Ku-Band Signals in the Tropics

Journal of Electromagnetic Waves and Applications, 2005

ABSTRACT Simultaneous measurements of Ku-band attenuation and rain-rate give A 0.01 and R 0.01 as... more ABSTRACT Simultaneous measurements of Ku-band attenuation and rain-rate give A 0.01 and R 0.01 as 9.7 dB and 54 mm/hr respectively, Unlike the monotonous variation predicted by the ITU-R model, breakpoints were observed in both the rain-rate and Ku-band attenuation exceedances. Similar observations were reported from other stations in the tropics. The accumulation time factor measured at the breakpoints remained almost a constant in these stations. Using this it is predicted that for stations with high elevation angle receivers, at breakpoint rain-rates, one rain-cell intercepts the propagation path of the signal. It is estimated that, in the tropics, the diameter of a rain-cell is 1.5 km when the rain-rate begin to saturate.