Effect of Boundary Layer Dynamics on the Profiles of Rain Drop Size Distribution During Convective Rain
TL;DR: The profiles of rain microstructures have been investigated for different types of precipitation using microrain radar observations at a tropical location Kolkata and a prominent dip in radar reflectivity profile has been observed near the boundary layer at high rain rates.
Abstract: The profiles of rain microstructures have been investigated for different types of precipitation using microrain radar observations at a tropical location Kolkata (22.57° N, 88.37° E). A prominent dip in radar reflectivity ( $Z$ ) profile has been observed near the boundary layer at high rain rates. This phenomenon is due to the break-up of raindrops into smaller sizes at around 2 km height during intense convective events. The boundary layer dynamics decides the dominance of one of the two processes, namely, coalescence and break-up of rain drops, and determines the drop size distribution profile near the boundary layer. A sharp gradient of vertical velocity at 1–2 km heights is responsible for enhanced drop break-up resulting in an increase in the small drop number density.
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TL;DR: In this paper, the authors investigated the regional variability of summertime DSD in Beijing, using the DSD observations from ten disdrometer sites from April to September 2017, and analyzed the characteristics of DSD for both convective and stratiform precipitation, mainly classified by rain rate.
Abstract: Regional raindrop size distribution (DSD) features are poorly understood due to the lack of observations. Here we investigate the regional variability of summertime DSD in Beijing, using the DSD observations from ten disdrometer sites from April to September 2017. The characteristics of DSD are analyzed for both convective and stratiform precipitation, mainly classified by rain rate (R). The shape (μ) and slope (λ) parameters follow a second-degree polynomial regression relationship for both stratiform and convective precipitation. On average, stratiform precipitation is found to have larger values of μ and λ than convective precipitation, whereas convective precipitation has a larger mass-weighted mean diameter (Dm) and a generalized intercept parameter (Nw). Interestingly, the north of Beijing has larger values of μ and λ, as opposed to Dm and Nw that exhibit greater values in the south, which could probably be attributed to terrain differences. The rain rate dependence on DSD is analyzed as well. In general, the Dm-R and Nw-R relationships follow a power-law distribution, and both Dm and Nw increase significantly with R. As the rain rate increases, Dm keeps increasing to around 1.5 mm until an equilibrium state is reached. The findings obtained here could provide useful reference for better estimations of rainfall using the remote sensing techniques.
13 citations
10 citations
Cites background from "Effect of Boundary Layer Dynamics o..."
...As the bigger raindrops fall from this region, their growth accelerates by CC (Hashiguchi, Kozu, et al., 2016; Maitra et al., 2019; Zhou et al., 2020)....
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Journal Article•
TL;DR: In this paper, the drop size distributions, based on the images obtained in 6-s samples (about 750 m of flight track), are used to calculate both radar reflectivity Z and rain rate R.
Abstract: Raindrop images obtained on research flights of the NCAR Electra aircraft in the Tropical Oceans Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE) are analyzed. The drop size distributions, based on the images obtained in 6-s samples (about 750 m of flight track), are used to calculate both radar reflectivity Z and rain rate R. Airborne radar data from the NOAA P-3 aircraft flying in coordination with the Electra are used to categorize the particle-image data according to whether the drop images were obtained in regions of convective or stratiform precipitation. Within stratiform precipitation, the same rain rate could be produced by a drop spectrum dominated by numerous small drops (lower reflectivity) or by a few large drops (higher reflectivity). The reflectivity values varied by as much as 9 dB for a given rain rate. Reflectivity data from the airborne radar and flight-level data reveal that the stratiform regions often contain fallstreaks of about 0.1‐2 km in horizontal dimension. The fallstreaks are associated with large-drop spectra and local maxima in reflectivity up to approximately 40 dB Z and in rain rates up to 25 mm h21. The fallstreaks extend downward from the melting band and bend with the low-level wind shear, but do not usually reach the surface. Thus, although relatively more uniform than convective regions, stratiform regions can be variable in reflectivity and rain rate at fine spatial scales in both the horizontal and vertical directions. Stratiform regions are therefore best characterized by their ensemble properties rather than the values of individual high-resolution measurements. The variability of stratiform drop size spectra arises primarily from the occurrence of fallstreaks and the discontinuous nature of regions favoring aggregation of snow crystals, and it implies that Z‐R distributions associated with convective and stratiform precipitation are not statistically distinct. Thus, separate Z‐R relations for convective and stratiform precipitation are not justified, and techniques to distinguish between convective and stratiform precipitation based solely on the characteristics of drop size distributions are not likely to be accurate. The variability of the drop size spectra in tropical precipitation makes an exponential fit to the Z‐R relation sensitive to the spatial scale over which Z and R are determined. This sensitivity can be avoided by using a probability-matched Z‐R relation. The probability-matched Z‐R relation for all the raindrop image data from the Electra collected between altitudes of 2.7 and 3.3 km in TOGA COARE is similar to the Z‐R relation obtained at the sea surface in the Global Atmospheric Research Program Atlantic Tropical Experiment.
10 citations
TL;DR: A comparative analysis between the percentage of stratiform and convective rain durations shows significant dominance of strat Uniformitarian rain over convectiveRain at the present location showssignificant dominance of Stratiform rain over Convective rain.
Abstract: This article aims to classify precipitation into two categories, namely stratiform and convective. Multiple techniques, such as utilizing the micro rain radar (MRR), electric field monitor (EFM), radiometer, and disdrometer measurements, have been deployed for this purpose, at a tropical location Kolkata, India. A new rain classification technique, using logistic regression modeling of the sixth to third moment ratio ${(M6/M3)}$ , has been proposed. Classification of rain types based on the new technique shows high consistency with that based on radar reflectivity ( ${Z}$ ) values obtained from disdrometer measurements. This article also distinguishes mixed rain from stratiform and convective rain. The observations on the bright band structure by MRR and on differential brightness temperature at 31.4 and 22.23 GHz by a radiometer are utilized to classify mixed rain types. Although the EFM measurements do not classify rain types directly, they give a distinct signature of the impending stratiform/convective rain events. A comparative analysis between the percentage of stratiform and convective rain durations shows significant dominance of stratiform rain over convective rain. At the present location, the convective phenomenon shows higher occurrences during the pre-monsoon period compared to the monsoon period.
6 citations
Cites background or methods from "Effect of Boundary Layer Dynamics o..."
...Utilizing EFM measurements, stratiform and convective precipitation cannot be classified directly, but it can be shown that the atmospheric electric field in terms of potential gradient (PG) [14], [31]...
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...In this article, the MRR was operated in 30-s sampling intervals at 200-m range resolution, and consequently the maximum measurable height that can be attained is 6000 m [14]....
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TL;DR: In this article , the impacts of reduced anthropogenic activities during the lockdown period of COVID-19 pandemic on the aerosol concentration, treated as heat absorbing agent, and on the related atmospheric processes, using ground-based and spaceborne measurements over a highly polluted Indian metropolis, Kolkata.
Abstract: The present study addresses the impacts of reduced anthropogenic activities during the lockdown period of COVID-19 pandemic on the aerosol concentration, treated as heat absorbing agent, and on the related atmospheric processes, using ground-based and spaceborne measurements over a highly polluted Indian metropolis, Kolkata. The investigation reveals that reduced aerosol concentrations during the pre-monsoon of 2020, when the lockdown was implemented, decreased atmospheric instability as indicated by low values of the convective available potential energy (CAPE). This hindered the abundance of aerosols above the atmospheric boundary layer. Also, micro rain radar (MRR) observations showed a significant reduction of convective precipitation occurrences over Kolkata during this period. The back trajectory analysis has revealed the absence of continental component toward the wind clusters associated with rain occurrences during pre-monsoon 2020. This resulted in increased occurrences of stratiform rain events during the pre-monsoon of 2020 compared to the same period of previous years.
4 citations
References
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25 Feb 2004
TL;DR: The instructor's manual to a work which introduces the fundamental principles of meteorology, explaining storm dynamics and the dynamics of climate and its global implications is described in this paper, where the authors present a detailed discussion of the relationship between meteorology and climate.
Abstract: The instructor's manual to a work which introduces the fundamental principles of meteorology, explaining storm dynamics and the dynamics of climate and its global implications.
4,185 citations
Book•
01 Jan 1972
TL;DR: The instructor's manual to a work which introduces the fundamental principles of meteorology, explaining storm dynamics and the dynamics of climate and its global implications is described in this paper, where the authors present a detailed discussion of the relationship between meteorology and climate.
Abstract: The instructor's manual to a work which introduces the fundamental principles of meteorology, explaining storm dynamics and the dynamics of climate and its global implications.
2,061 citations
TL;DR: In this paper, a simplified cumulus parameterization scheme, suitable for use in GCMs, is presented, based on a plume ensemble concept similar to that originally proposed by Arakawa and Schubert (1974).
Abstract: A simplified cumulus parameterization scheme, suitable for use in GCMs, is presented. This parameterization is based on a plume ensemble concept similar to that originally proposed by Arakawa and Schubert (1974). However, it employs three assumptions which significantly simplify the formulation and implementation of the scheme. It is assumed that an ensemble of convective‐scale updrafts with associated saturated downdrafts may exist when the atmosphere is locally conditionally unstable in the lower troposphere. However, the updraft ensemble is comprised only of those plumes which are sufficiently buoyant to penetrate through this unstable layer. It is assumed that all such plumes have the same upward mass flux at the base of the convective layer. The third assumption is that moist convection, which occurs only when there is convective available potential energy (CAPE) for reversible ascent of an undiluted parcel from the sub‐cloud layer, acts to remove CAPE at an exponential rate with a specified...
1,655 citations
"Effect of Boundary Layer Dynamics o..." refers background in this paper
...Zhang and McFarlane [19] have suggested that the strong downdrafts are a common characteristic of shallow and deep convection resulting in an unstable and randomly fluctuating state of the atmosphere....
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TL;DR: In this article, the terminal velocities for distilled water droplets falling through stagnant air are accurately determined using a new method employing electronic techniques, and the over-all accuracy of the massterminal-velocity measurements is better than 0.7 per cent.
Abstract: The terminal velocities for distilled water droplets falling through stagnant air are accurately determined. More than 1500 droplets of mass from 0.2 to 100,000 micrograms, embracing droplets so small that Stokes' law is obeyed up to and including droplets so large that they are mechanically unstable, were measured by a new method employing electronic techniques. An apparatus for the production of electrically charged artificial water droplets at a controllable rate is described. The over-all accuracy of the mass-terminal-velocity measurements is better than 0.7 per cent.
1,465 citations
TL;DR: In this paper, a three-parameter gamma distribution was used for dual-measurement techniques to determine rainfall rate, and the relationship between pairs of integral rainfall parameters using a three parameter gamma drop size distribution was investigated.
Abstract: Empirical analyses are shown to imply variation in the shape or analytical form of the raindrop size distribution consistent with that observed experimentally and predicted theoretically. These natural variations in distribution shape are demonstrated by deriving relationships between pairs of integral rainfall parameters using a three parameter gamma drop size distribution and comparing the expressions with empirical. There comparisons produce values for the size distribution parameters which display a systematic dependence of one of the parameters on another between different rainfall types as well as from moment to moment within a given rainfall type. The implications of this finding are explored in terms of the use of a three-parameter gamma distribution in dual-measurement techniques to determine rainfall rate.
1,237 citations
"Effect of Boundary Layer Dynamics o..." refers methods in this paper
...Dm has been calculated using the following relation [29]:...
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