[1] Dual-Doppler and polarimetric radar observations are used to analyze two mesoscale convective systems (MCSs) that occurred during the Tropical Rainfall Measuring Mission Large-Scale Biosphere-Atmosphere field campaign. The MCSs formed in different meteorological regimes, based on profiles of atmospheric wind and thermodynamic data. The first MCS event (26 January 1999) was a squall line that formed in low-level easterly flow and had an intense leading line of convection. In contrast, the 25 February 1999 MCS formed in low-level westerly flow and was best characterized by stratiform precipitation with embedded convective elements. The radar analyses suggest that the MCSs were distinct in terms of overall vertical structure characteristics. In particular, polarimetric radar cross sections indicated the presence of an active mixed phase zone in the easterly MCS that was largely absent in the westerly case. The easterly MCS had considerably more precipitation ice in the middle to upper troposphere compared to the westerly MCS. Composite analyses showed that the easterly MCS had higher peak reflectivities and a smaller reflectivity gradient above the 0°C level in convective regions of the storm compared to the westerly MCS event. Moreover, mean profiles of both vertical air motion and vertical mass transport in the convective portion of the easterly MCS were larger (over a factor of 2 at some heights below the 0° C level) than those in the westerly event. These observations suggest that the easterly and westerly wind regimes in the southwest Amazon region produce convection with different vertical structure characteristics, similar to regimes elsewhere in the global tropics (e.g., maritime continent).

Radar observations of the kinematic, microphysical, and precipitation characteristics of two MCSs in TRMM LBA : Large-scale biosphere-atmosphere experiment in Amazonia (LBA)

. Lightning activity constitute the major destructive component of
thunderstorms over India. Hence, an understanding of the long-term variability
in lightning occurrence and intensity and their interrelation with various
causative factors is required. Long-term (1998–2014) Tropical Rainfall
Measuring Mission (TRMM) satellite-based lightning observations depict the
most frequent lightning occurrences along the Himalayan foothills, the
Indo-Gangetic plains and coastal regions, while the intensity of these
lightning strikes is found to be strongest along the coastal regions and in the
Bay of Bengal. In addition, both of the abovementioned lightning properties show a very strong
intensification ( ∼  1 %–2.5 % annually) across all Indian
regions during the 1998–2014 period with the maximum trends along the coasts.
Accordingly, a detailed statistical dominance analysis is performed which
reveals total column water vapor (TCWV) to be the dominant factor behind the
intensification in lightning events, while instability, measured by the
convective available potential energy (CAPE), and aerosol optical depth
(AOD) jointly control the lightning frequency trends. An increase in surface
temperatures has led to enhanced instability and, hence, stronger moisture
transport to the upper-troposphere and lower-stratosphere regions, especially along the coasts. This transported moisture helps deplete the ozone
concentration, leading to reduced temperatures and elevated equilibrium
levels, which finally results in stronger and more frequent lightning events,
as also evidenced by the trend analysis. Consequently, the relationships
between lightning and its causative factors have been expressed in the form of
multilinear regression equations, which are then employed in multiple global
circulation models (GCMs) to understand the long-term impact of urbanization
on lightning over the period from 1950 to 2100. The analysis reveals a uniform
increase in lightning occurrence and intensity using both urbanization
scenarios; however, accelerated growth is observed in the RCP8.5
projections after the year 2050, as also observed from the surface warming
trends. As a result, lightning frequency and intensity values across the
Indian region are expected to increase ∼  10 %–25 % and 15 %–50 %, respectively, by the end of the century with the
highest risk along the coasts; hence, this requires immediate attention
from policymakers.

/pdf/lightning-occurrences-and-intensity-over-the-indian-region-3p5tclan8e.pdf

Lightning occurrences and intensity over the Indian region: long-term trends and future projections

https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/asl.957

Influence of aerosols on lightning activities in central eastern parts of China

Hubei Province Region (HPR), located in Central China, is a concentrated area of severe convective weather. Three severe convective processes occurred in HPR were selected, namely 14–15 May 2015 (Case 1), 6–7 July 2013 (Case 2), and 11–12 September 2014 (Case 3). In order to investigate the differences between the three cases, the temporal and spatial distribution characteristics of cloud–ground lightning (CG) flashes and precipitation, the distribution of radar parameters, and the evolution of cloud environment characteristics (including water vapor (VD), liquid water content (LWC), relative humidity (RH), and temperature) were compared and analyzed by using the data of lightning locator, S-band Doppler radar, ground-based microwave radiometer (MWR), and automatic weather stations (AWS) in this study. The results showed that 80% of the CG flashes had an inverse correlation with the spatial distribution of heavy rainfall, 28.6% of positive CG (+CG) flashes occurred at the center of precipitation (>30 mm), and the percentage was higher than that of negative CG (−CG) flashes (13%). Moreover, the quantity of thunderstorm cells in Case 1 was more than other cases, the peak time of +CG flashes was prior to that of total CG flashes in Case 2 and Case 3, and the time of +CG flashes’ peak in Case 2 was prior to that of precipitation at about 2 h. Based on the analysis of the cloud environment, there are three main reasons for the differences of CG flashes and precipitation. Firstly, the structure of the LWC vertical profile and the height of the LWC peak are different, and high LWC makes it difficult for the collision of ice particles to generate electricity. Secondly, the differences between convective available potential energy (CAPE), precipitation, and CG flashes is caused by the sudden increase of VD from 1.5 km to 3 km, and thirdly, the production of CG flashes is very sensitive to RH at the surface layer and the total CG flashes increase as the RH increasing.

https://www.mdpi.com/2073-4433/10/6/298/pdf

Analysis of Lightning and Precipitation Activities in Three Severe Convective Events Based on Doppler Radar and Microwave Radiometer over the Central China Region

Characteristics of lightning-caused wildfires in central Brazil in relation to cloud-ground and dry lightning

Ten-year measurements of lightning and relative humidity from 2002 2011 have been analyzed in the Nanjing city, China. Statistical analysis shows the lightning density is positively correlated to relative humidity during this period. To further investigate the effect of relative humidity on electrification and lightning discharges in thunderstorms, a two-dimensional cumulus model incorporating dynamics, microphysics, and thunderstorm electrification mechanisms is used to present a sensitive study. The results show that the higher relative humidity in surface leads to more cloud droplet and stronger updraft, because of enhanced latent heat releasing from increasing condensation. Greater updraft and cloud water content primarily contribute to stronger ice crystal and graupel particles production with increasing relative humidity. A greater formation of cloud droplet, graupel and ice crystal result in increasing charge separation via non-inductive and inductive mechanism. The total lightning flashes increase as the relative humidity increase from 60 90%, and only tests with high relative humidity of 90% can produce negative cloud to ground (CG) flashes and positive CG flashes. In addition, the increase of relative humidity condition generally leads to a quicker and stronger convection, which results in earlier electrification and lightning discharges in thunderstorm. Article history: Received 25 January 2018 Revised 5 August 2018 Accepted 6 September 2018

/pdf/effects-of-relative-humidity-on-electrification-and-hplfzp9ce6.pdf

Effects of relative humidity on electrification and lightning discharges in thunderstorms

The effect of aerosols on lightning has been noted in many studies, but much less is known about the long-term impacts in air-polluted urban areas of China. In this paper, 9-year data sets of cloud-to-ground (CG) lightning, aerosol optical depth (AOD), convective available potential energy (CAPE), and surface relative humidity (SRH) from ground-based observation and model reanalysis are analyzed over three air-polluted urban areas of China. Decreasing trends are found in the interannual variations of CG lightning density (unit: flashes km−2day−1) and total AOD over the three study regions during the study period. An apparent enhancement in CG lightning density is found under conditions with high AOD on the seasonal cycles over the three study regions. The joint effects of total AOD and thermodynamic factors (CAPE and SRH) on CG lightning density and the percentage of positive CG flashes (+CG flashes/total CG flashes × 100; PPCG; unit: %) are further analyzed. Results show that CG lighting density is higher under conditions with high total AOD, while PPCG is lower under conditions with low total AOD. CG lightning density is more sensitive to CAPE under conditions with high total AOD.

Cloud-to-Ground Lightning Response to Aerosol over Air-Polluted Urban Areas in China

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Effects of relative humidity on electrification and lightning discharges in thunderstorms

Cloud-to-Ground Lightning Response to Aerosol over Air-Polluted Urban Areas in China