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Evolution of C-band dual-Doppler analysis of (a)–(f) radar reflectivity and (g)–(l) vertical velocity for the flash case at the times shown. Black dots indicate radiation sources from the OK-LMA plotted in the frame closest to when the lightning flash occurred. Pink dot indicates flash initiation point. The letters ''n'' in (e) and (f) denote the cell that formed to the west of the main convective area.
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Two small multicellular convective areas within a larger mesoscale convective system that occurred on 20 June 2004 were examined to assess vertical motion, radar reflectivity, and dual-polarimetric signatures between flash and non-flash-producing convection. Both of the convective areas had similar life cycles and general structures. Yet, one case...
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... flashes that occurred with this area initiated in a transition zone between the updraft and the downdraft in the mixed-phase region and occurred above the greatest reflectivity values near the front of the storm (Fig. 6). The interface between updrafts and downdrafts would likely be associated with strong charge separation zones as lower-density particles are carried upward relative to heavier, more-dense, particles. Lund et al. (2009) found a similar tendency for flash initiations to occur in regions of strong vertical velocity gradients in the storm ...
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... characterize the evolution of each convective area, east-west-oriented vertical cross sections of radar reflec- tivity and vertical motion were taken through the 1.25-km MSL reflectivity maxima of each convective zone from all six dual-Doppler analyses (Figs. 6 and 7). Both regions exhibited typical multicellular activity with new cells pri- marily forming on the downshear (east) side of the exist- ing ...
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... flash-producing case started as a fairly narrow convective feature (Fig. 6a) that widened with time as new precipitation developed in response to the ;8 m s 21 updraft pulse observed at 1548 UTC (Fig. 6g). The depth of reflectivity greater than 42 dBZ increased from 1548 to 1553 UTC. From 1551 to 1553 UTC (Figs. 6b and 6c) the main cell appeared to be at its mature stage, though the updraft had already ...
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... flash-producing case started as a fairly narrow convective feature (Fig. 6a) that widened with time as new precipitation developed in response to the ;8 m s 21 updraft pulse observed at 1548 UTC (Fig. 6g). The depth of reflectivity greater than 42 dBZ increased from 1548 to 1553 UTC. From 1551 to 1553 UTC (Figs. 6b and 6c) the main cell appeared to be at its mature stage, though the updraft had already decreased significantly in strength (Figs. 6h and 6i). The strongest reflectivity values through the depth of the storm were on the east ...
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... flash-producing case started as a fairly narrow convective feature (Fig. 6a) that widened with time as new precipitation developed in response to the ;8 m s 21 updraft pulse observed at 1548 UTC (Fig. 6g). The depth of reflectivity greater than 42 dBZ increased from 1548 to 1553 UTC. From 1551 to 1553 UTC (Figs. 6b and 6c) the main cell appeared to be at its mature stage, though the updraft had already decreased significantly in strength (Figs. 6h and 6i). The strongest reflectivity values through the depth of the storm were on the east side, or the forward edge of the convective zone. By 1556 UTC (Fig. 6d), a descending reflectivity core can be in- ...
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... time as new precipitation developed in response to the ;8 m s 21 updraft pulse observed at 1548 UTC (Fig. 6g). The depth of reflectivity greater than 42 dBZ increased from 1548 to 1553 UTC. From 1551 to 1553 UTC (Figs. 6b and 6c) the main cell appeared to be at its mature stage, though the updraft had already decreased significantly in strength (Figs. 6h and 6i). The strongest reflectivity values through the depth of the storm were on the east side, or the forward edge of the convective zone. By 1556 UTC (Fig. 6d), a descending reflectivity core can be in- ferred and updraft values had dropped below 5 m s 21 with a modest 3-4 m s 21 convective downdraft from mid-to low levels (Fig. 6j). ...
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... from 1548 to 1553 UTC. From 1551 to 1553 UTC (Figs. 6b and 6c) the main cell appeared to be at its mature stage, though the updraft had already decreased significantly in strength (Figs. 6h and 6i). The strongest reflectivity values through the depth of the storm were on the east side, or the forward edge of the convective zone. By 1556 UTC (Fig. 6d), a descending reflectivity core can be in- ferred and updraft values had dropped below 5 m s 21 with a modest 3-4 m s 21 convective downdraft from mid-to low levels (Fig. 6j). Despite the rapid weakening of the core of the storm, the first flash occurred around this time. Reflectivity values continued to decrease through 1601 UTC ...
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... strength (Figs. 6h and 6i). The strongest reflectivity values through the depth of the storm were on the east side, or the forward edge of the convective zone. By 1556 UTC (Fig. 6d), a descending reflectivity core can be in- ferred and updraft values had dropped below 5 m s 21 with a modest 3-4 m s 21 convective downdraft from mid-to low levels (Fig. 6j). Despite the rapid weakening of the core of the storm, the first flash occurred around this time. Reflectivity values continued to decrease through 1601 UTC (Figs. 6e and 6f), as did updraft strength (Figs. 6k and 6l). Reflectivity values greater than 40 dBZ were located almost entirely below the freezing level; yet, this is about the ...
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... UTC (Fig. 6d), a descending reflectivity core can be in- ferred and updraft values had dropped below 5 m s 21 with a modest 3-4 m s 21 convective downdraft from mid-to low levels (Fig. 6j). Despite the rapid weakening of the core of the storm, the first flash occurred around this time. Reflectivity values continued to decrease through 1601 UTC (Figs. 6e and 6f), as did updraft strength (Figs. 6k and 6l). Reflectivity values greater than 40 dBZ were located almost entirely below the freezing level; yet, this is about the time the second flash occurred (1600:50 UTC). The stronger updrafts in Figs. 6k and 6l on the left (west) side of the cross sections correspond to a new cell forming to the ...
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... core can be in- ferred and updraft values had dropped below 5 m s 21 with a modest 3-4 m s 21 convective downdraft from mid-to low levels (Fig. 6j). Despite the rapid weakening of the core of the storm, the first flash occurred around this time. Reflectivity values continued to decrease through 1601 UTC (Figs. 6e and 6f), as did updraft strength (Figs. 6k and 6l). Reflectivity values greater than 40 dBZ were located almost entirely below the freezing level; yet, this is about the time the second flash occurred (1600:50 UTC). The stronger updrafts in Figs. 6k and 6l on the left (west) side of the cross sections correspond to a new cell forming to the west side of the collapsing cell (see Figs. ...
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... the early stages of the flash-producing case, at 1548 UTC (Fig. 7a) the null case exhibited a narrow reflectivity zone. Though it was narrower than the flash case, stronger reflectivity values were observed, espe- cially at lower levels. The initial upward impulse was not as strong as the flash-producing case (cf. Figs. 6g and 7g). Between 1551 and 1556 UTC, the null case appeared to be at its mature phase, having reached a peak updraft intensity of about 6 m s 21 at 1551 UTC (Fig. 7h). As in the flash-producing case, the strongest reflectivity values were on the east side (forward edge) of the storm (Figs. 7b-d). By 1558 UTC, the null case started to merge with ...
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... Yang et al., 2020). The large vertical wind shear facilitates thunderstorm organization to form multicellular storms and broad updrafts (Fuchs et al., 2015;Palucki et al., 2011). The mei-yu thunderstorm had a larger mean area of radar echo than the post-mei-yu thunderstorm (Table 1) and tended to be more organized. ...
... Above the level of −10°C, the proportion of graupel during the mei-yu thunderstorm was more than that of the post-mei-yu thunderstorm (Figures 3a and 3b). The environmental characteristics showed that the regional mean vertical wind shear (700-1,000 hPa) was 15 m s −1 during the mei-yu period ( Table 1) Palucki et al., 2011). The mei-yu thunderstorm had a larger area of radar echo than the post-mei-yu thunderstorm (Table 1) and tended to be more organized. ...
... The mei-yu thunderstorm had a larger area of radar echo than the post-mei-yu thunderstorm (Table 1) and tended to be more organized. Broad updrafts are hypothesized to be less prone to entrainment of ambient air, causing less depleting cloud liquid water and can bring a larger fraction of SLWC to the mixed-phase region (Palucki et al., 2011;E. R. Williams et al., 1991;Zipser, 2003). ...
Using polarimetric radar, cloud‐to‐ground (CG) lightning, and reanalysis data, this study examined the microphysical structures of thunderstorm and their environmental impact during two active monsoon periods over Nanjing, Yangtze River Delta. The results show that the mei‐yu thunderstorm presented a large area of radar echo and many graupels between 0 and −10°C levels; these were accompanied by large vertical wind shear, which was favorite for the organization of thunderstorm. Broad updrafts within the mei‐yu thunderstorms were hypothesized, causing lower amount of dilution and entrainment, facilitating transportation of supercooled liquid water to the mixed‐phase region and producing CG lightning. Due to large atmospheric instability, strong updrafts within the post‐mei‐yu thunderstorm were expected to supply supercooled liquid water for the riming process to form more graupel above −10°C level. These provided favorable conditions for electrification, resulting in more CG lightning during the post‐mei‐yu period than during the mei‐yu period.
... However, increasing the Nyquist interval can enhance the potential for range ambiguities, which may overlap and contaminate first-trip signals (Zrnić and Mahapatra 1985). In operational and research applications, rigorous postprocessing of radar data must be performed to conduct range unfolding and remove range overlaid echoes and to dealias radial velocities for use in numerical weather prediction models (Montmerle and Faccani 2009;Dong and Xue 2013;Shen et al. 2016), observational analysis such as dual and multi-Doppler wind syntheses (Biggerstaff and Houze 1991;Palucki et al. 2011;DiGangi et al. 2016;Betten et al. 2018;Alford et al. 2019aAlford et al. ,b, 2020, and severe weather detection (Mitchell et al. 1998;Joe et al. 2004;Smith et al. 2016). ...
Mobile weather radars at high frequencies (C, X, K and W-band) often collect data using staggered Pulse Repetition Time (PRT) or dual Pulse Repetition Frequency (PRF) modes to extend the effective Nyquist velocity and mitigate velocity aliasing while maintaining a useful maximum unambiguous range. These processing modes produce widely dispersed “processor” dealiasing errors in radial velocity estimates. The errors can also occur in clusters in high shear areas. Removing these errors prior to quantitative analysis requires tedious manual editing and often produces “holes” or regions of missing data in high signal-to-noise areas. Here, data from three mobile weather radars were used to show that the staggered PRT errors are related to a summation of the two Nyquist velocities associated with each of the PRTs. Using observations taken during a mature mesoscale convective system, a landfalling tropical cyclone, and a tornadic supercell storm, an algorithm to automatically identify and correct staggered PRT processor errors has been developed and tested. The algorithm creates a smooth profile of Doppler velocities using a Savitzky-Golay filter independently in radius and azimuth and then combined. Errors are easily identified by comparing the velocity at each range gate to its smoothed counterpart and corrected based on specific error characteristics. The method improves past dual PRF correction methods that were less successful at correcting “grouped” errors. Given the success of the technique across low, moderate, and high radial shear regimes, the new method should improve research radar analyses by affording the ability to retain as much data as possible rather than manually or objectively removing erroneous velocities.
... Our analysis results indicate that HD grids, especially SD grids, tend to be formed in a stable temperature range (−29.0 to −44.7 °C), and this range seems to be colder than the main temperature range (0 to −30 °C) of non-inductive electrification [39,[53][54][55]. Many previous observations found that the strong updraft present in the mixed phase zone is important for the production of lightning [56][57][58][59][60][61][62][63][64][65][66]. Furthermore, the simulation study indicated that the main electrification processes usually occur within regions with a consistent, instead of necessarily a very strong, updraft [67]. ...
... Our analysis results indicate that HD grids, especially SD grids, tend to be formed in a stable temperature range (−29.0 to −44.7 • C), and this range seems to be colder than the main temperature range (0 to −30 • C) of non-inductive electrification [39,[53][54][55]. Many previous observations found that the strong updraft present in the mixed phase zone is important for the production of lightning [56][57][58][59][60][61][62][63][64][65][66]. Furthermore, the simulation study indicated that the main electrification processes usually occur within regions with a consistent, instead of necessarily a very strong, updraft [67]. ...
To investigate the characteristics of regions exhibiting multiple lightning initiations within a finite volume and a short time, the lightning location data obtained from the convective regions of 14 mesoscale convective systems were analyzed in combination with data from radar. In total, 415 out of 5996 radar grids (1 km × 1 km × 0.5 km) were found to initiate more than one flash within 6 min. Only 49 grids showed an initiation density of more than two flashes within 6 min. The grids with high flash initiation densities were found to have a similar distribution to those with one lightning initiation within 6 min, in terms of altitude and reflectivity relative to altitude. They also showed similar trends in their frequency evolution. The grids with higher initiation densities seemed to be more concentrated in the altitude range of 9–13 km. However, only one was found to form at a lower altitude near the melting level when lightning initiation clearly declined. Moreover, the spatial relationship of this lower higher-initiation density grid to the reflectivity core was different to that in the main altitude range. In this paper, the possible dynamic and electrical mechanisms of the formation of this lower higher-initiation density grid are discussed.
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... The melting of larger graupel particles (e.g. Palucki et al. 2011;Mattos et al. 2016) could have a substantial contribution to the surface rainfall. However, quantification of the same is lacking. ...
... In the convective regime, 93 characterized by stronger updraft, the precipitation particles grow by accretion of cloud liquid 94 water, a process known as coalescence in the warm phase of cloud and riming in the mixed 95 phase region (Houghton, 1968). In lightning-producing-clouds associated with stronger 96 updraft, larger and numerous graupel particles formed by riming of supercooled water in the 97 mixed phase region of cloud (Palucki et al., 2011;Mattos et al., 2016) where they take part in 98 the electrification of cloud through non-inductive charging process . ...
... 524Palucki et al., 2011;Mattos et al., 2016) may also have some contribution to the surface 525 rainfall. However, quantification of the same is lacking. ...
The thesis addresses a long-standing problem of the electrical effect in rain formation processes in tropical atmospheric conditions. It has been shown that the electrification of clouds has important implications for cloud and rain microphysical processes. The electric field beneath a thunderstorm enhances the size of raindrops by enhancing the coalescence of raindrops. It is also shown that lightning can enhance the surface rainfall intensity by electrifying the raindrops near the lightning channel.
... Palucki et al., 2011;Geerts et al., 2017). Doppler velocities from two or more radar perspectives are used to estimate the three-dimensional flow in these scenarios to understand a storm's evolution and structure . ...
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... The radar data were interpolated onto a Cartesian grid (100 km × 90 km with a 0.75 km horizontal spacing and 0.25 to 18.25 km AGL in the vertical with 0.5 km spacing) using a hybrid Cressman [51] and natural neighbor [52] weighting scheme. The wind synthesis was performed using the National Center for Atmospheric Research (NCAR) software package Custom Editing and Display of Reduced Information in Cartesian Space (CEDRIC; [53]) following a procedure similar to that of Palucki et al. [54]. To maintain consistent resolvable scales throughout the 90-minute period of the analysis, the wind retrievals employed a two-step Leise [55] filter which dampened wavelengths less than 4.5 km and eliminated wavelengths less than 3.0 km. ...
Nearly continuous wind retrievals every three minutes for an unprecedented 90-minute period were constructed during multiple mesocyclone cycles in a tornadic high-precipitation supercell. Asymptotic contraction rate analysis revealed the relationship between the primary and secondary rear-flank gust fronts (RFGF and SRFGFs) and the rear-flank downdraft (RFD) and occlusion downdrafts. This is thought to be the first radar-based analysis where the relationship between the near-surface gust fronts and their parent downdrafts has been explored for sequential mesocyclones. Changes in the SRFGFs were associated with surges in the RFD. During part of the mesocyclone lifecycle, the SRFGF produced a band of low-level convergence and associated deep updraft along the southwestern side of the hook echo region that ingested the RFD outflow and limited both entrainment into the RFD and reinforcement of low-level convergence along the leading edge of the primary RFGF. The second mesocyclone intensified from stretching in an occlusion updraft rather than in the primary updraft. This low-level mesocyclone remained well separated from the updraft shear region vorticity that was associated with a more traditional midlevel mesocyclone. However, the third mesocyclone initiated in the vorticity-rich region of the primary updraft zone and was amplified by stretching in the primary updraft.
... In fact, most of these param- eters directly reflect the characteristics of updraft. Observations have shown that the existence of a strong updraft in the mixed-phase region (-40-0℃) is necessary to produce lightning (Workman and Reynolds, 1949;Williams and Lhermitte, 1983;Dye et al., 1988;Rutledge et al., 1992;Carey and Rutledge, 1996;Petersen et al., 1996Petersen et al., , 1999Pickering et al., 1998;Baker et al., 1999;Black and Hallett, 1999;Wang et al., 2009;Heymsfield et al., 2010;Palucki et al., 2011;Yao et al., 2013;Zhang et al., 2013;Reinhart et al., 2014;Wang et al., 2015). Moreover, quantitative observational studies on the role of convective updrafts have been carried out. ...
The rate of neutralized charge by lightning (RNCL) is an important parameter indicating the intensity of lightning activity. The total charging rate (CR), the CR of one kind of polarity (e.g., negative) charge (CROP), and the outflow rate of charge on precipitation (ORCP) are proposed as key factors impacting RNCL, based on the principle of conservation of one kind of polarity charge in a thunderstorm. In this paper, the impacts of updraft on CR and CROP are analyzed by using a 3D cloud resolution model for a strong storm that occurred in Beijing on 6 september 2008. The results show that updraft both promotes and inhibits RNCL at the same time. (1) Updraft always has a positive influence on CR. The correlation coefficient between the updraft volume and CR can reach 0.96. Strengthening of the updraft facilitates strengthening of RNCL through this positive influence. (2) Strengthening of the updraft also promotes reinforcement of CROP. The correlation coefficient between the updraft volume and CROP is high (about 0.9), but this promotion restrains the strengthening of RNCL because the strengthening of CROP will, most of the time, inhibit the increasing of RNCL. (3) Additionally, increasing of ORCP depresses the strengthening of RNCL. In terms of magnitude, the peak of ORCP is equal to the peak of CR. Because precipitation mainly appears after the lightning activity finishes, the depression effect of ORCP on RNCL can be ignored during the active lightning period.
... It leads to the production of graupel as ice particles collect supercooled liquid cloud droplets at subfreezing temperatures (List 1982). In the midlatitudes, graupel is commonly observed in cumuli (Knight et al. 1974;Heymsfield 1978), severe thunderstorms (e.g., Deierling et al. 2005;Wiens et al. 2005;Kuhlman et al. 2006;Bruning et al. 2007; Kumjian et al. 2010;Palucki et al. 2011), mesoscale convective systems (e.g., Zrni c et al. 1993), and heavy snowstorms (e.g., Knight and Knight 1973;Schneebeli et al. 2013). In the Arctic, even within mixed-phase clouds, large graupel particles are not frequently observed because of weak upward velocities (e.g., Shupe et al. 2008;Lawson and Zuidema 2009) and/or low concentrations of liquid cloud droplets, and therefore low liquid water content, there (Jayaweera and Ohtake 1973). ...
Characteristics of graupel in an Arctic deep mixed-phase cloud on 7 December 2013 were identified with observations from an X-band scanning polarimetric radar and a Ka-band zenith pointing radar in conjunction with scattering calculations. The cloud system produced generating cells and strongly sheared precipitation fall streaks. The X-band radar hemispheric RHI observables revealed spatial sorting of polarimetric signatures: decreasing differential propagation phase shift (φDP), negative specific differential phase (KDP) collocated with negative differential reflectivity (ZDR) in the upper half of the fall streak and increasing or near-constant φDP with positive ZDR at the bottom edge of the fall streak. The negative KDP and ZDR, indicating pro-late particles with vertically-oriented maximum dimensions, were consistent with small, slow-falling conical graupel coexisting with low concentrations of more isometric graupel. The ob-served negative KDP values were best matched by scattering calculations for small, dense conical graupel with 30° to 40° cone angles. The positive KDP and ZDR and the Doppler spectra indicate that large isometric graupel coexisted with a second population of slower-falling rimed plate-like particles in the lower half of the fall streak. Through the core of the fall streak φDP decreased in range while ZDR was slightly positive, indicating that the prolate conical graupel dominated φDP while the isometric larger graupel dominated reflectivity (and thus ZDR). These results demonstrate the capability of polarimetric observables and Doppler spectra to distinguish different growth stages of rimed particles, allowing for the improvement of hydrometeor classification methods.
... Many observations have confirmed the connection between updraft and lightning activity. Some researchers believed that the strong updraft existing in the mixed phase zone (-40 to 0℃) is important for the production of lightning (Workman and Reynolds, 1949;Williams and Lhermitte, 1983;Dye et al., 1989;Rutledge et al., 1992;Carey and Rutledge, 1996;Petersen et al., 1996Petersen et al., , 1999Wang et al., 2009;Heymsfield et al., 2010;Zheng et al., 2010;Palucki et al., 2011;Reinhart et al., 2014). Zipser (1994) hypothesized that weak updrafts in most oceanic storms produce insufficient concentrations of supercooled liquid water, large ice particles, and ice-ice collisions in the mixed phase zone, which are otherwise essential for the electrification process leading to lightning. ...
A three-dimensional (3D) charging-discharging cloud resolution model was used to investigate the impact of the vertical velocity field on the charging processes and the formation of charge structure in a strong thunderstorm. The distribution and evolution of ice particle content and charges on ice particles were analyzed in different vertical velocity fields. The results show that the ice particles in the vertical velocity range from 1 to 5 m s−1 obtained the most charge through charging processes during the lifetime of the thunderstorm. The magnitude of the charges could reach 1014 nC. Before the beginning of lightning activity, the charges produced in updraft region 2 (updraft speed ⩾ 13 m s−1) and updraft region 1 (updraft speed between 5 and 13 m s−1) were relatively significant. The magnitudes of charge reached 1013 nC, which clearly impacted upon the early lightning activity. The vertical velocity conditions in the quasi-steady region (updraft speed between −1 and 1 m s−1) were the most conducive for charge separation on ice particles on different scales. Accordingly, a net charge structure always appeared in the quasi-steady and adjacent regions. Based on the results, a conceptual model of ice particle charging, charge separation, and charge structure formation in the flow field was constructed. The model helps to explain observations of the “lightning hole” phenomenon.
