Multi-technique observations of convective rain events at a tropical location
01 Aug 2014-pp 1-4
TL;DR: In this paper, the effects of the convective rain on various atmospheric parameters have been investigated at Kolkata (22.57°N, 88.37°E), India, during pre-monsoon and monsoon period of 2013.
Abstract: The effects of the convective rain on various atmospheric parameters have been investigated at Kolkata (22.57°N, 88.37°E), India, during pre-monsoon and monsoon period of 2013. Various parameters like cloud base height and depth, liquid water content, rain rate and rain drop size distribution (DSD) are observed concurrently. The atmospheric electric field measured with an electric field monitor and the attenuation and depolarisation of satellite signals measured by a Ku-band receiving system are also studied during rain events. The instability indices obtained from radiometric measurements and the rain height profiles from micro rain radar are used to classify rain into two types, namely, convective and stratiform. The signatures of rain events on multi-technique observations are studied to indicate the various aspects of convective processes at a tropical location.
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TL;DR: In this article , the authors used an electric field monitor (EFM) at a tropical urban location, Kolkata (22.65°N, 88.45°E).
Abstract: Nowcasting of lightning occurrences is essential in tropical locations as lightening causes severe damage to life and property. This study attempts to nowcast lightning events during convective phenomena using an electric field monitor (EFM) at a tropical urban location, Kolkata (22.65°N, 88.45°E). Before the onset of heavy lightning occurrences, definite changes in the atmospheric electric field (EF) are observed, which in turn are associated with high cloud liquid water content (LWC) and low cloud base height (CBH). A model has been proposed to nowcast lightning strikes within about 17.5 km radius of the present location based on the EF standard deviation (EFSD) values. The proposed technique is tested with the lightning data provided by a collocated lightning detector, which yields a prediction efficiency of ~ 0.91 (~ 0.86), a false alarm rate of ~ 0.23 (~ 0.18), and a critical success index of ~ 0.71 (~ 0.72) with an optimal range of other performance parameters during the monsoon (pre-monsoon) periods, thereby generating an alarm 45 min before lightning events.
Proceedings Article•
01 Oct 2016
TL;DR: In this paper, features of convective rain in respect of liquid water content, rain rate profile, and electric field variation have been identified, and multi-frequency radiometric brightness temperatures are used to nowcast impending rain events and rain fall amount.
Abstract: Characterization of convective rain at tropical station Kolkata, located near the land-ocean boundary, in the eastern part of India, has been made using observations from multi-frequency radiometer, micro rain radar, disdrometer and electric field monitor. Features of convective rain in respect of liquid water content, rain rate profile, and electric field variation have been identified. Multi-frequency radiometric brightness temperatures are used to nowcast impending rain events and rain fall amount.
01 Jul 2018
TL;DR: The observations with a micro rain radar (MRR), an FMCW radar, over Kolkata, have been utilized to study the drop size distribution and its relationship with radar reflectivity at Ka-band, indicating that the increased downdraft causes breakup of rain drops into smaller sizes.
Abstract: Boundary layer dynamics play an important role in determining precipitation structure during convective processes. The radar reflectivity profiles which depend on the sixth moment of rain drop size distribution (DSD) can be employed to sense the precipitation processes. The height profiles of DSD significantly depend on the vertical wind velocity. The observations with a micro rain radar (MRR), an FMCW radar, over Kolkata, have been utilized to study the drop size distribution and its relationship with radar reflectivity at Ka-band. A sharp decrease of radar reflectivity in the height range 1–2 km corresponds to an increase of downdraft velocity observed around the same height range. This indicates that the increased downdraft causes breakup of rain drops into smaller sizes. The split in the Doppler spectrum, known as aliasing effect, is most prominent near the boundary layer height and has been employed to estimate downward wind velocity.
Cites background from "Multi-technique observations of con..."
...The boundary layer dynamics plays an important role in the evolution of rain drop size distribution (DSD) during convective rain events, which constitute an important meteorological phenomenon at tropical locations [1-2]....
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References
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TL;DR: In this article, the feasibility of nowcasting convective activity is examined by using thermodynamic indices derived from the ground-based microwave radiometer (MWR) observations located at a tropical station, Gadanki (13.5°N, 79.2°E).
Abstract: [1] In the present study, the feasibility of nowcasting convective activity is examined by using thermodynamic indices derived from the ground-based microwave radiometer (MWR) observations located at a tropical station, Gadanki (13.5°N, 79.2°E). There is a good comparison between thermodynamic parameters derived from MWR and colocated GPS radiosonde observations, indicating that MWR observations can be used to develop techniques for nowcasting severe convective activity. Using MWR observations, a nowcasting technique was developed with the data of 26 thunderstorm cases observed at Gadanki. The analysis showed that there are sharp changes in some thermodynamic indices, such as the K index, the humidity index, precipitable water content, the stability index, and equivalent potential temperature lapse rates, about 2–4 h before the occurrence of thunderstorm. A superepoch analysis was made to examine the composite temporal variations of the thermodynamic indices associated with the occurrence of thunderstorms. The superepoch analysis revealed that 2–4 h prior to the storm occurrence, appreciable variations in many parameters are observed, suggesting thermodynamic evolution of the boundary layer convective instability. It is further demonstrated that by monitoring these variations it is possible to predict the ensuing thunderstorm activity over the region at least 2 h in advance. The association between the temporal evolution of thermodynamic indices and convective activity has been tested for the independent case of nine thunderstorms. The present results suggest that ground-based MWR observations can be used effectively to predict the occurrence of thunderstorms at least 2 h in advance.
313 citations
TL;DR: In this article, the authors evaluated the skill of the convective parameters and indices to predict thunderstorms by means of probability distribution functions, probabilities of thunderstorms according to an index threshold, and skill scores like the Heidke Skill Score (HSS) that are based on categorical verification.
Abstract: . The preconvective environment on days with ordinary, widespread, and severe thunderstorms in Southwest Germany was investigated. Various thermodynamic and kinetic parameters calculated from radiosoundings at 12:00 UTC were verified against subsequent thunderstorm observations derived from SYNOP station data, radar data, and damage reports of a building insurance company. The skill of the convective parameters and indices to predict thunderstorms was evaluated by means of probability distribution functions, probabilities of thunderstorms according to an index threshold, and skill scores like the Heidke Skill Score (HSS) that are based on categorical verification. For the ordinary decision as to whether a thunderstorm day was expected or not, the best results were obtained with the original Lifted Index (80% prediction probability for LI≤−1.73; HSS=0.57 for LI≤1.76), the Showalter Index, and the modified K-Index. Considering days with isolated compared to widespread thunderstorms, the best performance is reached by the Deep Convective Index. For days with severe thunderstorms that caused damage due to hail, local storms or floods, the best prediction skill is found again for the Lifted Index and the Deep Convective Index, but also for the Potential Instability Index, the Delta-θe Index, and a version of the CAPE, where the lifting profile is determined by averaging over the lowest 100 hPa.
139 citations
"Multi-technique observations of con..." refers background in this paper
...At the same time, the EFM and CBH values also decrease indicating an impending local convective development before the event....
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...As cloud approaches EFM, it senses positive field lines from cloud top and shows an increase in electric field....
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...For the present study, we have utilized the following measurements pertaining to the period of May-September 2013: (i) atmospheric electric field from EFM, (ii) CBH, LWC, CAPE, and TTI from radiometer, (iii) rain rate and rain DSD from disdrometer, (iv) vertical profile of rain rate and melting layer from MRR, and (v) rain attenuation and depolarization of Ku-band satellite signal....
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...Generally cloud bases are negatively and tops are positively charged and its field line distribution affects atmospheric electric field which can be observed with an electric field monitor (EFM) [3]....
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...The EFM-100 is an atmospheric electric field monitor which uses a mechanical chopper to alternately shield and expose several sense plates to an electric field thus allowing it to measure the electric field as an AC voltage across the sense resistor....
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TL;DR: In this article, the degradation of cross-polarization discrimination due to rain over the Earth space path has been obtained from these measurements and compared to that estimated from the ITU-R model, indicating the characteristic feature of a tropical location.
Abstract: The phenomenon of depolarization of a Ku-band satellite signal caused by rain has been studied with a simple experimental system in which the attenuation of the copolar component and the enhancement of the cross-polar component signal have been measured at a tropical location. The degradation of cross-polarization discrimination (XPD) due to rain over the Earth space path has been obtained from these measurements and compared to that estimated from the ITU-R model, indicating the characteristic feature of a tropical location.
17 citations
"Multi-technique observations of con..." refers background in this paper
...1(b) shows the large raindrops in the range of 3-4 mm which are also responsible for large depolarization of the signal indicated by a significant cross polar enhancement of the satellite signal [6]....
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...This system can monitor attenuation and depolarization of the Ku- band satellite signals [6]....
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TL;DR: In this article, the strong convective activities manifested through rainfall during the cyclone were studied with multi-technique observations involving micro rain radar, disdrometer, rain gauges, and a Ku-band satellite signal receiving system.
Abstract: A severe cyclone, named Aila, passed over Kolkata on 25 May 2009. The strong convective activities manifested through rainfall during the cyclone were studied with multi-technique observations involving micro rain radar, disdrometer, rain gauges, and a Ku-band satellite signal receiving system. A number of features of precipitation, namely the presence of large rain drops, the large vertical extent of the precipitating layer, an unusual enhancement of cross-polar component, and strong scintillations of the co-polar component of the satellite signal due to strong turbulences associated with the cyclone, were observed. This study leads to a more comprehensive understanding of the precipitation associated with a cyclonic storm.
16 citations
"Multi-technique observations of con..." refers background in this paper
...[2] reported that a cyclonic storm caused significant propagation effects on Ku-band satellite signal due to strong turbulence associated with the cyclone....
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TL;DR: In this article, two ground-based instruments were designed and built in order to accomplish the present research, one based on the principle of the induction ring, measuring the electric charge as well as the size of individual raindrops.
Abstract: Two ground-based instruments were designed and built in order to accomplish the present research. The first, based on the principle of the induction ring, measures the electric charge as well as the size of the individual raindrops. The other is a novel raingage providing the instantaneous value of the rainfall rate: a U-shaped tube turns the rainwater flow into an airflow more easily measured by a sensitive airflow meter. The adjustable range has been set between 1 and 100 mm h−1. Six spring showers were investigated. Individual electric charges between 5 and 100 pC have been measured on raindrops up to 4 mm in diameter. The data reduction shows that each shower must be studied separately, using several parameters. Under these conditions, there are two distinct types of precipitation, according to the sign of the charge excess they provide. The total charge carried down by each shower is primarily determined by the greater number of drops of one sign as compared to the other sign. Cross-correlat...
15 citations