Thunderstorm activity and the structure of tropical cyclones

The paper investigates lightning activity in the region of tropical cyclones (TC), its structure and changeability during the process of TC development and attenuation according to the data of the World Wide Lightning Location Network (WWLLN) as well as the relation with ocean surface wind fields according to the ASCAT scatterometer data. Distribution of lightning discharges in TC regions and discharge density fields drawn up from them allowed us to detect TC structure elements, such as mesovortexes, eyewalls, cloud bands and spirals, and to trace their change in space and time.

Lightning‐generated whistler waves are electromagnetic plasma waves in the very low frequency (VLF) band, which play an important role in the dynamics of radiation belt particles. In this paper, we statistically analyze simultaneous waveform data from the Van Allen Probes (Radiation Belt Storm Probes, RBSP) and global lightning data from the World Wide Lightning Location Network (WWLLN). Data were obtained between July to September 2013 and between March and April 2014. For each day during these periods, we predicted the most probable 10 min for which each of the two RBSP satellites would be magnetically conjugate to lightning producing regions. The prediction method uses integrated WWLLN stroke data for that day obtained during the three previous years. Using these predicted times for magnetic conjugacy to lightning activity regions, we recorded high time resolution, burst mode waveform data. Here we show that whistlers are observed by the satellites in more than 80% of downloaded waveform data. About 22.9% of the whistlers observed by RBSP are one‐to‐one coincident with source lightning strokes detected by WWLLN. About 40.1% more of whistlers are found to be one‐to‐one coincident with lightning if source regions are extended out 2000 km from the satellites footpoints. Lightning strokes with far‐field radiated VLF energy larger than about 100 J are able to generate a detectable whistler wave in the inner magnetosphere. One‐to‐one coincidences between whistlers observed by RBSP and lightning strokes detected by WWLLN are clearly shown in the L shell range of L = 1–3. Nose whistlers observed in July 2014 show that it may be possible to extend this coincidence to the region of L≥4.

Characteristics of tropical cyclones (TCs) in global climate models (GCMs) are known to be influenced by details of the model configurations, including horizontal resolution and parameterization schemes. Understanding model-to-model differences in TC characteristics is a prerequisite for reducing uncertainty in future TC activity projections by GCMs. This study performs a process-level examination of TC structures in eight GCM simulations that span a range of horizontal resolutions from 1° to 0.25°. A recently developed set of process-oriented diagnostics is used to examine the azimuthally averaged wind and thermodynamic structures of the GCM-simulated TCs. Results indicate that the inner-core wind structures of simulated TCs are more strongly constrained by the horizontal resolutions of the models than are the thermodynamic structures of those TCs. As expected, the structures of TC circulations become more realistic with smaller horizontal grid spacing, such that the radii of maximum wind (RMW) become smaller, and the maximum vertical velocities occur off the center. However, the RMWs are still too large, especially at higher intensities, and there are rising motions occurring at the storm centers, inconsistently with observations. The distributions of precipitation, moisture, and radiative and surface turbulent heat fluxes around TCs are diverse, even across models with similar horizontal resolutions. At the same horizontal resolution, models that produce greater rainfall in the inner-core regions tend to simulate stronger TCs. When TCs are weak, the radial gradient of net column radiative flux convergence is comparable to that of surface turbulent heat fluxes, emphasizing the importance of cloud–radiative feedbacks during the early developmental phases of TCs.

On Aug. 29, 2016, the tropical cyclone Lionrock was reported to turn into an extra-tropical storm and go to the shore of the Primorsky Region as monitoring shows, which brought about significant precipitation growth recorded in the north of the coast. Many surveys show the tropical cyclones in this area to transform into extra-tropical ones and become powerful mid-latitude storms with significant damage to coastal and maritime areas. The paper uses WWLLN (World Wide Lightning Location Network) data to study the thunderstorm activity while the tropical cyclone reaches the typhoon level with the maximum wind velocity. This made it possible to identify parameters’ variations of thunderstorm activity during atmospheric vortex phenomena. It also enabled us to determine the emergency probability due to a thunderstorm.

Extremely low frequency (ELF) and very low frequency (VLF) observations have formed the cornerstone of measurement and interpretation of effects of lightning discharges on the overlying upper atmospheric regions, as well as near‐Earth space. ELF (0.3–3 kHz) and VLF (3–30 kHz) wave energy released by lightning discharges is often the agent of modification of the lower ionospheric medium that results in the conductivity changes and the excitation of optical emissions that constitute transient luminous events (TLEs). In addition, the resultant ionospheric changes are best (and often uniquely) observable as perturbations of subionospherically propagating VLF signals. In fact, some of the earliest evidence for direct disturbances of the lower ionosphere in association with lightning discharges was obtained in the course of the study of such VLF perturbations. Measurements of the detailed ELF and VLF waveforms of parent lightning discharges that produce TLEs and terrestrial gamma ray flashes (TGFs) have also been very fruitful, often revealing properties of such discharges that maximize ionospheric effects, such as generation of intense electromagnetic pulses (EMPs) or removal of large quantities of charge. In this paper, we provide a review of the development of ELF and VLF measurements, both from a historical point of view and from the point of view of their relationship to optical and other observations of ionospheric effects of lightning discharges.

Thunderstorm activity is indirectly taken into account when using statistics on forest fires. Another way is to use the data of the lightning discharge finding sensors. This chapter proposes using the data of the World Wide Lightning Location Network (WWLLN). To assess the probability of forest fire occurrence, it is necessary to know the energy and the spatial distribution of lightning discharges. For the analysis of the data of the storm-direction-finding WWLLN, it is proposed to use clustering algorithms. For the computational experiment, the region covering the Timiryazevskiy forestry of the Tomsk region (55.93 - 56.86) on the north, (83.94 - 85.07), and the data on lightning discharges registered by the WWLLN network in this region in July 2014. The sample data were 273 lightning discharges. The results of clustering are presented, as well as the image of the silhouette index for each object, the average value of the ASW index for grouping solutions obtained using the complete, kmeans, and dbscan algorithms.

We compare radio atmospherics (sferics) detected by the World Wide Lightning Location Network (WWLLN) to very low frequency (VLF) whistler waves observed in the low‐latitude ionosphere by the Vector Electric Field Instrument of the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. We also model the propagation of these sferics through the Earth‐ionosphere waveguide to the subsatellite point using the Long‐Wavelength Propagation Capability software and compare this result to the same C/NOFS data set. This unprecedentedly expansive data set allows comparison to theory and prior observation of VLF radio wave propagation in the Earth‐ionosphere waveguide and low‐latitude ionosphere. We show that WWLLN and C/NOFS observe the well‐known effect of variable attenuation with direction within the Earth‐ionosphere waveguide. Propagation within the ionosphere is also examined, and a lack of attenuation above 400 km is observed. Finally, in comparison to recent works using Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) data by Fiser et al. and Chum et al., we find that C/NOFS successfully detects whistlers with comparable amplitudes at much greater distances, compared to those reported for DEMETER.

: The long-term goal of this project is to improve the prediction of tropical cyclone (TC) genesis, structure, and intensity changes through improved representation of 3-dimensional TC structure in operational weather forecast models. The accurate prediction of TC genesis, structure, and intensity changes is critical to Navy missions and civilian activities in coastal areas. Significant gains have been made in TC track prediction over the past decades. However, genesis and intensity forecasts have shown very little progress during the same time period. A primary contributing factor to our lack of skill in predicting TC genesis and intensity is an inadequate representation of initial axisymmetric and asymmetric TC dynamic and thermodynamic structures. TC initialization is a universal problem in nearly all current operational weather forecast systems, as indicated in a recent HFIP workshop. By conducting both idealized Observation System Simulation Experiments (OSSE) and real-case TC forecast experiments, we intend to tackle the weaknesses in current operational weather forecast models. We propose a combined TC dynamic initialization-3DVar data assimilation approach. The key component of this new scheme is a TC dynamic initialization (TCDI) package. The TCDI package includes three steps. The first step is the decomposition of the TC vortex from its environmental field. The second step is a dynamic initialization with the full nonlinear dynamics and physics, which forces the first guess field toward the observed central minimum pressure, given realistic asymmetric heating profiles. The third step is to add the newly generated TC field into the environmental field and use it in the subsequent 3DVar assimilation. After the TCDI is completed, the 3Dvar assimilation follows. A preliminary OSSE study was conducted and the results show that this new approach greatly improves both TC symmetric and asymmetric dynamic and thermodynamic patterns.

Many patients with severe obstructive sleep apnea (OSA) do not complain of excessive daytime sleepiness (EDS), possibly due to increased sympathetic nervous activity (SNA) and accompanying heightened alertness. We hypothesized that in patients with OSA, those without subjective EDS (Epworth Sleepiness Scale, ESS score < 11) would have higher very low frequency (VLF) heart rate variability (HRV) during sleep, reflecting greater sympathetic heart rate modulation than patients with an ESS score ≥ 11. Patients with severe OSA (AHI ≥ 30: 26 with and 65 without heart failure) were divided into those with and without EDS. Heart rate (HR) signals were acquired in stage 2 sleep during periods of recurrent apneas and hypopneas and submitted to coarse graining spectral analysis, which extracts harmonic, neurally mediated contributions to HRV from total spectral power. Because the apnea-hyperpnea cycle entrains muscle SNA at VLF (0 to 0.04 Hz), VLF power was our principal between-group comparison. Subjects without EDS had higher harmonic VLF power (944 ± 839 vs 447 ± 461 msec(2), p = 0.003) than those with EDS, irrespective of the presence or absence of heart failure (1218 ± 944 vs 426 ± 299 msec(2), p = 0.043, and 1029 ± 873 vs 503 ± 533 msec(2), p = 0.003, respectively). ESS scores correlated inversely with VLF power in all (r = -0.294, p = 0.005) and in heart failure subjects (r = -0.468, p = 0.016). Patients with severe OSA but without EDS have higher VLF-HRV than those with EDS. This finding suggests that patients with severe OSA but without EDS have greater sympathetic modulation of HRV than those with EDS that may reflect elevated adrenergically mediated alertness. Taranto Montemurro L; Floras JS; Picton P; Kasai T; Alshaer H; Gabriel JM; Bradley TD. Relationship of heart rate variability to sleepiness in patients with obstructive sleep apnea with and without heart failure.

The results of a study of thunderstorm activity in the structure of tropical cyclones are presented. Various sources provide somewhat conflicting data on the relationship between the time of development of the intensity of thunderstorm activity and the phases of development of tropical cyclones. Seven tropical cyclones with the greatest impact on Primorye and Kamchatka in August 2016 were considered. An analysis of the data showed that powerful bursts of lightning activity are observed during the transition from the depression stage to the storm stage during the development of a tropical cyclone. The transition to the typhoon stage is preceded by similar bursts of lightning activity, lasting at least an hour. Moreover, an increase in lightning activity is usually ahead of a sharp increase in winds and, accordingly, the transition of a tropical cyclone to the next stage by several hours. It was also established that in three of the seven cases considered, during the dissipation of a tropical cyclone, a powerful burst of lightning activity is also observed.

The mean kinematic and thermodynamic structures of tropical cyclones (TCs) making landfall in mainland China are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanied with a decrease in low-level wind speed, an expansion of the radius of strong wind, weakening of the upper-level warm core, and drying of the mid-tropospheric air. On average, the warm core of the TCs dissipates 24 h after landfall. The height of the maximum low-level wind and the base of the stable layer both increase with the increased distance to the TC center; however, the former is always higher than the latter. In particular, an asymmetric structure of the TC after landfall is found. The kinematic and thermodynamic structures across various areas of TC circulation differ, especially over the left-front and right-rear quadrants (relative to the direction of TC motion). In the left-front quadrant, strong winds locate at a smaller radius, the upper-level temperature is warmer with the warm core extending into a deep layer, while the wet air occupies a shallow layer. In the right-rear quadrant, strong wind and wet air dwell in an area that is broader and deeper, and the warmest air is situated farther away from the TC center.

Lightning data from the World Wide Lightning Location Network (WWLLN) are used to document the lightning characteristics in tropical cyclones (TCs) making landfall in China. The landfall period is confined to 48 h prior to and after landfall (t-24∼t+24). Data from a total of 74 TCs are collected from 2010 to 2020, providing 3,293 individual time periods (1-h periods). To examine the radial and asymmetry distributions as a function of TC intensity, landing location, and vertical wind shear, the dataset is classified into two intensity categories, three shear groups, and four landing locations. WWLLN detected lightning activity in all TCs during the 48-h landfall, with lightning rates most frequently appearing between 250 and 600 str h−1. Extreme hourly lightning rates of 3,154 str h−1 and 4,426 str h−1 are observed in the inner core in Tropical Storm Cimaron (2013) and the outer rainbands in Severe Typhoon Matmo (2014), respectively, comparable to lightning activity in mesoscale convection systems on land. TCs landing in Guangdong and Hainan have the largest peak lightning rates, while those landing in Zhejiang and Shanghai show the lowest lightning rates. The maximum lightning density is found in the inner-core region of weak TCs (&amp;lt;32.7 m s−1) that are located approximately 100–200 km away from the coastline. The radial distribution of lightning density at landing stages is consistent with that at mature stages when TCs are over the ocean. However, there is a shift in the lightning maximum from the inner core prior to landfall (t-24∼t0) to the outer rainbands after landfall (t0∼t+24), indicating the effects of dry continental air intrusion and the enhanced surface frictional convergence. Vertical wind shear is the dominant factor in producing lightning and convective asymmetry for TCs landing in all locations. Lightning asymmetries are enhanced with the increase in shear magnitude from low (&amp;lt;5 m s−1) to moderate (5–10 m s−1) and high (&amp;gt;10 m s−1) shear environments, both in weak and strong TCs (≥32.7 m s−1).

A parallel VLF radio noise spectrometer has been used at a testing ground of the ShICRA SB RAS for recording ionospheric-magnetospheric radio emissions since 1972. The site located at a distance of 30 km from Yakutsk (62 N, 129.72 E). A one-point lightning discharge recorder was also installed at the site, which consists of a whip and two crossed loop antennas, an amplifier, an ADC, and a PC with a special program. The same direction finder with a change in gain and a special program can work as a narrow-sector direction finder for fluctuating radio noise. To investigate the function of propagation of VLF signals, narrowband radio noise, and their dependence on the space weather parameters, a VLF signal recorder that has been operating continuously in Yakutsk since 2009 is used. The World Wide Lightning Location Network (wwlln.net) data have been used for lightning discharge location since 2009. One of the WWLLN receivers was installed in Yakutsk. One-point lightning guides called “LD-250” and “Storm Tracker” for recording the coordinates of a lightning discharge and its type have been used for discharge registration within a territory of 400 km in radius around Yakutsk since 2006.

In this paper the impacts of vertical resolution on the simulations of Typhoon Talim (2005) are examined using the Weather Research and Forecasting (WRF) model, with cumulus parameterization scheme representing the cumulus convection implicitly. It is shown that the tropical cyclone (TC) track has little sensitivity to vertical resolution, whereas the TC intensity and structure are highly sensitive to vertical resolution. It is partly determined by the sensitivity of the planetary boundary layer (and the surface layer) and the cumulus convection processes to vertical resolution. Increasing vertical resolution in the lower layer could strengthen the TC effectively. Increasing vertical resolution in the upper layer is also beneficial for the storm intensification, but to a lesser degree. In contrast, improving the midlevel resolution may cause the convergence of environmental air, which inhibits the TC intensification. The results also show that the impacts of vertical resolution on features of the TC structure, such as the tangential winds, secondary circulations and the evolution of the warm-core structure, are consistent with the impacts on the TC intensity. It is suggested that in the simulations of TCs, the vertical levels should be distributed properly rather than the more the better, with higher vertical resolution being expected both in the lower and upper layer, while the middle layer should not hold too many levels.

Abstract. Lightning is an important source of NOx in the free troposphere, especially in the tropics, with strong impact on ozone production. However, estimates of lightning NOx (LNOx) production efficiency (LNOx per flash) are still quite uncertain. In this study we present a systematic analysis of NO2 column densities from SCIAMACHY measurements over active thunderstorms, as detected by the World-Wide Lightning Location Network (WWLLN), where the WWLLN detection efficiency was estimated using the flash climatology of the satellite lightning sensors LIS/OTD. Only events with high lightning activity are considered, where corrected WWLLN flash rate densities inside the satellite pixel within the last hour are above 1 /km2/h. For typical SCIAMACHY ground pixels of 30 × 60 km2, this threshold corresponds to 1800 flashes over the last hour, which, for literature estimates of lightning NOx production, should result in clearly enhanced NO2 column densities. From 2004–2008, we find 287 coincidences of SCIAMACHY measurements and high WWLLN flash rate densities. For some of these events, a clear enhancement of column densities of NO2 could be observed, indeed. But overall, the measured column densities are below the expected values by more than one order of magnitude, and in most of the cases, no enhanced NO2 could be found at all. Our results are in contradiction to the currently accepted range of LNOx production per flash of 15 (2–40)×1025 molec/flash. This probably partly results from the specific conditions for the events under investigation, i.e. events of high lightning activity in the morning (local time) and mostly (for 162 out of 287 events) over ocean. Within the detected coincidences, the highest NO2 column densities were observed around the US Eastcoast. This might be partly due to interference with ground sources of NOx being uplifted by the convective systems. However, it could also indicate that flashes in this region are particularly productive. We conclude that current estimates of LNOx production might be biased high for two reasons. First, we observe a high variability of NO2 for coincident lightning events. This high variability can easily cause a publication bias, since studies reporting on high NOx production have likely been published, while studies finding no or low amounts of NOx might have been rejected as errorneous or not significant. Second, many estimates of LNOx production in literature have been performed over the US, which is probably not representative for global lightning.