Thunderstorm Cells Research Articles

Simulation of mesoscale structure of thunderstorm using ARPS Model

In this paper mesoscale structures of two thunderstorm events over Delhi have been simulated using ARPS (Advanced Regional Prediction System) model. Numerical experiments were carried out using radiosonde data of Delhi and applying a potential temperature perturbation for triggering convective activity. The simulation exercise demonstrates strong updrafts and downdrafts associated with the thunderstorm cells, indicating the presence of very strong localized convection. The development and evolution of thunderstorm and propagation of associated precipitation zone are clearly brought out in this simulation study.

ELF transients associated with sprites and elves in eastern Mediterranean winter thunderstorms

During the northern hemisphere winter of 2005–2006, transient luminous events (TLEs) known as ‘sprites’ and ‘elves’ were imaged over thunderstorm cells in the eastern Mediterranean. Simultaneously, extremely low frequency (ELF) data (ELF: 3–3000 Hz) were recorded at two observation stations in Israel and Hungary in order to qualify and quantify parameters of the parent lightning discharge associated with the transient optical emissions in the upper atmosphere. In this study, we found that for 87% (Israel) and 77% (Hungary) of optically observed TLEs an intense ELF transient event was recorded. These stations are located some 500 and 2100 km, respectively, from the region of the TLEs. All ELF transients that were associated with TLEs were caused by lightning discharges with positive polarity. Calculation of the charge moment change showed values between 600 and 2800 C km with a peak around 1000 C km. Additionally, the time delay between the +CG and ensuing sprite was 76±34 ms and it was displaced up to 50 km from its parent CG. One of our objectives in the present study was to characterize, based on the ELF radiation from lightning, the electromagnetic (EM) waveforms of the lightning discharges which generate TLEs in the time and frequency domains, and to compare them with other lightning discharges occurring in the same thunderstorm cell at approximately the same time, but which did not produce TLEs. The survey for a typical EM waveform showed no unique ELF signature for lightning discharges associated with either sprites or elves.

Microtornadoes under a Nanocrystalline Igloo: Results Predicting a Worldwide Intensification of Tornadoes

When a sessile water drop of radius R containing polystyrene nanospheres evaporates in an open Petri dish, the nanospheres eventually form a dense layer of nanoclay enclosed by a ring of radius r ≤ R. When it evaporates in a closed Petri dish, the predominant structure is a crystalline ring with a thin nanoclay film in its interior. When it evaporates in a closed and well-sealed Petri dish, securing a constantly high vapor pressure, instead of a ring, a crystalline igloo with multiple cells emerges. Light microscopy complemented by scanning electron microscopy provides evidence for vortices in the igloo (one per cell), which could only be formed by microtornadoes. Tornadoes with intense vortices are distinctive for thunderstorm cells (supercells) in association with deep moist convection driven by pre-existing warmer humid air at the ground, overrun by a cold front. A precondition for realistic tornadogenesis studies based on experimental models is the coexistence of a humid air layer at the ground with a...

An algorithm on convective weather potential in the early rainy season over the Pearl River Delta in China

This paper describes the procedure and methodology to formulate the convective weather potential (CWP) algorithm. The data used in the development of the algorithm are the radar echoes at 0.5° elevation from Guangzhou Doppler Radar Station, surface observations from automatic weather stations (AWS) and outputs of numeric weather prediction (NWP) models. The procedure to develop the CWP algorithm consists of two steps: (1) identification of thunderstorm cells in accordance with specified statistical criteria; and (2) development of the algorithm based on multiple linear regression. The thunderstorm cells were automatically identified by radar echoes with intensity greater than or equal to 50 dB(Z) and of an area over 64 square kilometers. These cells are generally related to severe convective weather occurrences such as thunderstorm wind gusts, hail and tornados. In the development of the CWP algorithm, both echo-and environment-based predictors are used. The predictand is the probability of a thunderstorm cell to generate severe convective weather events. The predictor-predictand relationship is established through a stepwise multiple linear regression approach. Verification with an independent dataset shows that the CWP algorithm is skillful in detecting thunderstorm-related severe convective weather occurrences in the Pearl River Delta (PRD) region of South China. An example of a nowcasting case for a thunderstorm process is illustrated.

Evidence for synchronicity of lightning activity in networks of spatially remote thunderstorms

Visual observations by space shuttle astronauts have described a phenomenon in which spatially distant thunderstorm cells seem to reciprocally “ignite” lightning flashes in a semi-cyclic sequence. Lightning occurring in one cell is immediately followed by lightning in other cells, separated by tens or hundreds of kilometers. We present quantitative analysis of lightning observations conducted within the framework of the MEIDEX-sprite campaign on board the space shuttle Columbia in January 2003 [Yair, Y., Israelevich, P., Devir, A., Moalem, M., Price, C., Joseph, J., Levin, Z., Ziv, B., Teller, A., 2004. New sprites observations from the space shuttle. Journal of Geophysical Research 109, D15201/10.1029/2003JD004497]. Video footage of 6 storm systems with varying flash rates, which occurred over Africa, South America, Australia and the Pacific Ocean were analyzed. It is found that when the storm flash rate was high, lightning activity in horizontally remote electrically active cells became clustered, with bursts of nearly simultaneous activity separated by quiet periods. The recurrence time was ∼2.5 s, close to the previously reported time delay between consecutive ELF transient signals in the Schumann resonance range [Füllekrug, M., 1995. Schumann resonances in magnetic filed components. Journal of Atmospheric and Terresterial Physics 57, 479–484]. We propose that this behavior is similar to the collective dynamics of a network of weakly coupled limit-cycle oscillators [Strogatz, S.H., 2000, From Kuramoto to Crawford: exploring the onset of synchronization in populations of coupled oscillators. Physica, D, 1–20]. Thunderstorm cells embedded within a mesoscale convective system (MCS) constitute such a network, and their lightning frequency is best described in terms of phase-locking of a globally coupled array [Kourtchatov, S.Y., Yu, V.V., Likhanskii, V.V., Napartovitch, A.P., Arecchi, F.T., Lapucci, A., 1995 Theory of phase locking of globally coupled laser arrays. Phys. Rev. A 52, 4089–4094]. Comparison of basic parameters of the lightning networks with predictions of random-graph models reveals that the networks cannot be described by the classical random-graph model [Erdos, P., Renyi, A., 1960. On the evolution of random graphs. Publ. Math. Inst. Hung. Acad. Sci., 5, 17–61], but are more compatible with generalized random-graphs with a prescribed degree distribution [Newman, M.E.J., Strogatz, S.H., Watts, D.J., 2001. Random graphs with arbitrary degree distributions and their applications. Phys. Rev. E 64, 026118] that exhibit a high clustering coefficient and small average path lengths. Such networks are capable of supporting fast response, synchronization and coherent oscillations [Lago-Fernandez, L.F., Huerta, R., Corbacho, F., Siguenza, J.A., 2000. Fast response and temporal coherent oscillations in small-world networks. Physical Review Letters 84, 2758–2761]. Several physical mechanisms are suggested to explain the observed phenomenon.

How do winter thundercloud systems generate sprite‐inducing lightning in the Hokuriku area of Japan?

Lightning and thundercloud systems leading to the generation of sprites were examined on the basis of analyses on the interrelation among radar reflectivity, lightning, and static electric field during the winter of 2004/2005 in the Hokuriku area of Japan. Eleven cases from the observed fifteen sprite events exhibit similar characteristics, so we present a typical case study of the thundercloud system. The analysis results are summarized as follows: (1) The sprite‐inducing +CG was triggered by a cloud flash produced by an active cell. (2) The sprite‐inducing +CG removed large positive charge from the stratiform region of another thunderstorm cell by the long linear lightning channel. (3) The origin of sprite‐inducing large positive charge appears to be located in the stratiform region.

Nowcasting Thunderstorm Anvil Clouds over Kennedy Space Center and Cape Canaveral Air Force Station

Abstract Electrified thunderstorm anvil clouds extend the threat of natural and triggered lightning to space launch and landing operations far beyond the immediate vicinity of thunderstorm cells. The deep convective updrafts of thunderstorms transport large amounts of water vapor, supercooled water droplets, and ice crystals into the upper troposphere, forming anvil clouds, which are then carried downstream by the prevailing winds in the anvil-formation layer. Electrified anvil clouds have been observed over the space launch and landing facilities of the John F. Kennedy Space Center and Cape Canaveral Air Force Station (CCAFS), emanating from thunderstorm activity more than 200 km away. Space launch commit criteria and flight rules require launch and landing vehicles to avoid penetration of the nontransparent portion of anvil clouds. The life cycles of 163 anvil clouds over the Florida peninsula and its coastal waters were documented using Geostationary Operational Environmental Satellite (GOES)-8 visible...

Spectroscopic measurements of NO2 in a Colorado thunderstorm: Determination of the mean production by cloud‐to‐ground lightning flashes

Ground‐based visible absorption spectroscopy of zenith‐scattered sky light was used to measure changes in the column abundance of NO2 during the passage of a thunderstorm over Boulder, Colorado, on September 12, 2002. The measurements showed a 10‐fold rise in slant column NO2 within the thunderstorm cell, consistent with an increase of about 7 ppbv in the lower core updrafts and main precipitation shaft. Mean mixing ratios of about 3 and 1.5 ppbv were inferred for the upper cell and anvil, respectively. These observations, together with measurements from the Denver NEXRAD and the Colorado State University (CSU) CHILL radars, and cloud‐to‐ground (CG) lightning flash data from the National Lightning Detection Network (NLDN), are used to estimate the flash mean production of NOx by CG lightning. The measurements suggest a mean production rate of (5.8 ± 2.9) × 1026 NOx molecules per CG flash, intermediate between the values derived from previous spectroscopic studies and in good agreement with the widely used value of 6.7 × 1026 NOx molecules per CG flash estimated by Price et al. [1997]. This agreement may be fortuitous, however, since the lightning in the present study was about a factor of two less energetic than the mean assumed by Price et al. and the production of (2.3 ± 1.4) × 1017 NOx/J inferred here is significantly larger than the value of 1 × 1017 NOx/J assumed in their calculations. These differences can be reduced, however, if the estimates of Price et al. are recalculated using newer peak current data from the NLDN, and more recently published flash energy production rates of Wang et al. [1998].

The Thunderstorm Interactive Forecast System: Turning Automated Thunderstorm Tracks into Severe Weather Warnings

Abstract The Australian Bureau of Meteorology has developed a new tool called the Thunderstorm Interactive Forecast System (TIFS; formerly known as ThunderBox) for interactively producing finished severe weather warnings and other forecasts from thunderstorm tracks, automatically diagnosed from radar data. TIFS is designed to apply recent advances in radar-based thunderstorm cell detection and tracking techniques to the efficient production of operational forecasts and warnings. The system ingests automated thunderstorm cell detections and tracks, allows graphical editing by forecasters, and produces graphical and text products from the edited data. The text generator uses a shallow, domain-specific approach. The graphical products include a map of areas that have been affected by storms, and are forecast to be affected by storms, as well as meteograms for selected locations.

Field measurement and experimental study of wind speed profile during thunderstorms

This paper investigates the variation of wind velocity with height during thunderstorms. Wind velocities during thunderstorms are measured at five levels on a 150 m tall tower. Velocity profiles for more than 50 thunderstorms are studied. In the analysis, these profiles are classified into four types according to the profile shape and the height of the highest wind speed. It is observed that wind profiles during thunderstorms are affected by several factors with the major ones being distance from the thunderstorm cell centre, intensity of the storm and ground roughness. Experimental studies on the simulation of thunderstorm wind using an impinging jet are also carried out to further investigate the effect of these parameters.

Resolution Requirements for the Simulation of Deep Moist Convection

The spatial resolution appropriate for the simulation of deep moist convection is addressed from a turbulence perspective. To provide a clear theoretical framework for the problem, techniques for simulating turbulent flows are reviewed, and the source of the subgrid terms in the Navier‐Stokes equation is clarified. For decades, cloud-resolving models have used large-eddy simulation (LES) techniques to parameterize the subgrid terms. A literature review suggests that the appropriateness of using traditional LES closures for this purpose has never been established. Furthermore, examination of the assumptions inherent in these closures suggests that grid spacing on the order of 100 m may be required for the performance of cloud models to be consistent with their design. Based on these arguments, numerical simulations of squall lines were conducted with grid spacings between 1 km and 125 m. The results reveal that simulations with 1-km grid spacing do not produce equivalent squallline structure and evolution as compared to the higher-resolution simulations. Details of the simulated squall lines that change as resolution is increased include precipitation amount, system phase speed, cloud depth, static stability values, the size of thunderstorm cells, and the organizational mode of convective overturning (e.g., upright towers versus sloped plumes). It is argued that the ability of the higher-resolution runs to become turbulent leads directly to the differences in evolution. There appear to be no systematic trends in specific fields as resolution is increased. For example, mean vertical velocity and rainwater values increase in magnitude with increasing resolution in some environments, but decrease with increasing resolution in other environments. The statistical properties of the simulated squall lines are still not converged between the 250- and 125-m runs. Several possible explanations for the lack of convergence are offered. Nevertheless, it is clear that simulations with O(1 km) grid spacing should not be used as benchmark or control solutions for resolution sensitivity studies. The simulations also support the contention that a minimum grid spacing of O(100 m) is required for traditional LES closures to perform appropriately for their design. Specifically, only simulations with 250- and 125-m grid spacing resolve an inertial subrange. In contrast, the 1-km simulations do not even reproduce the correct magnitude or scale of the spectral kinetic energy maximum. Furthermore, the 1-km simulations contain an unacceptably large amount of subgrid turbulence kinetic energy, and do not adequately resolve turbulent fluxes of total water. A guide to resolution requirements for the operational and research communities is proposed. The proposal is based primarily on the intended use of the model output. Even though simulations with O(1 km) grid spacing display behavior that is unacceptable for the model design, it is argued that these simulations can still provide valuable information to operational forecasters. For the research community, O(100 m) grid spacing is recommended for most applications, because a modeling system that is well founded should be desired for most purposes.

The physics of a thunderstorm

The salient facts concerning the dynamical, physical and electrical properties of athunderstorm, and of the detailed structure and associated electric field-changes oflightning flashes, are marshalled to deduce the criteria for a satisfactoryquantitative theory of charge generation and separation leading to thegrowth of electric fields strong enough to initiate and to sustain lightningactivity.A quantitative theory is presented of how charges are generatedand separated when supercooled cloud droplets make grazing contactwith the undersides of hail pellets (graupel) polarized initially by theEarth’s fine-weather electric field. The rebounding droplets acquire apositive charge and are carried by the convective updraught towards the topof the cloud, while the hail pellets carrying a net negative charge falltowards cloud base. This creates a vertical dipole field which increases thepolarizing charges on the hail pellets and so accelerates the rates of chargegeneration and separation, and so reinforces the vertical electrical field, whichgrows exponentially until insulation of the air breaks down and triggersa lightning flash.It is demonstrated that a thunderstorm cell, 2 km indiameter, producing small hail falling at 30 mm h−1can produce vertical electric fields of ∼5000 V cm−1in about 10 min involving the separation of ∼50 Cof charge, enough to initiate a lightning flash which, on average, neutralizes about20 C. As long as the hail persists, it continues to generate and separate sufficientcharge to produce a succession of lightning flashes at about 30 s intervals. Morefrequent discharges at say 10 s intervals would require high rates of hailproduction in larger cells but are more likely to be produced by largemulti-cellular storms sustained by strong convective currents for perhaps severalhours.

Analysis of an anomalously severe thunderstorm system over Northern Ireland

In Northern Ireland, as elsewhere in Europe, attempts to reduce the societal impacts of severe convective storms are constrained by underestimations in frequency and intensity of extreme events within the present-day climate regime. Such underestimations also present difficulties in estimating probabilities of extreme storm frequency and intensity in relation to future climate change scenarios. Detailed analyses of past extreme events enhance the robustness of hydrometeorological and climatological models, and improve human perception of the true nature of present climate. In Northern Ireland, extensive thunderstorm development is infrequent due to relatively low relief and limited severe convectional activity in summer. On 25–26 July 1985 extensive thunderstorm activity occurred accompanied by hailstones 3 cm in diameter, some of the largest on record to fall over the Province. The event predates operation of the Northern Ireland component of the UK rainfall radar network. Nevertheless, utilizing quality-controlled autographic rain gauge records and radiosonde data, the synoptic situation was examined and the mesoscale precipitation signatures determined throughout the duration of thunderstorm activity. Within the cyclonic circulation covering Northern Ireland for much of the day, potential instability existed at three levels and on release the buoyant upward motion resulted in clouds of more than 11 km in depth. While upland areas recorded 30 to 50 mm, the greatest precipitation totals of up to 85 mm were received in lowland areas around Lough Neagh. Several lowland sites recorded rainfall totals and intensities with frequencies of about 1 in 100 years. Significant thunderstorm activity occurred over a period of 11 h and resulted in serious flooding. Observed mesoscale precipitation patterns displayed limited evidence of orographic enhancement within the moist southeast to south airflow. At best, orography assisted in terms of initial uplift, but thereafter precipitation distribution was reliant upon thunderstorm cell structure and movement with input from local site and exposure influences. A factor possibly reducing the potential for marked orographic enhancement was the absence of strong winds at low levels. Mesoscale precipitation patterns suggested enhancement locally around the west and north shores of Lough Neagh. Energy exchanges between the Lough surface and the overlying atmosphere may have had repercussions upon water vapour content and buoyancy within the cyclonic south to southeasterly airflow, leading to this precipitation enhancement. Occurrence in the Mournes of hailstones 3 cm in diameter was indicative of the strength and endurance of the updraught component within individually propagating cells. The remarkable amounts and high intensities of rainfall, accompanied by large hailstone development, emphasized the importance of the synoptic event within the climatological history of Northern Ireland. With an absence of notable orographic enhancement of precipitation, the event also highlighted the occurrence of deviations from the mean precipitation patterns normally expected within cyclonic circulations.

Tornadoes in Portugal

In Portugal, research on tornadoes is very recent and has shown that they are not as rare as it is believed by public and even by scientific opinion. As tornadoes only affect a small area, the probability of their being observed at a meteorological station is very small. Thus, most of the existing records are people's recollections, some description in newspapers and some photos. It was possible to find data on 30 tornadoes that occurred from 1936 to 2002. This number is undoubtedly underestimated because the database is always under construction. Those tornadoes were moderate to strongly devastating, some of them causing great damage. The strongest tornado in Portugal, a T7 event, happened in November 1954. The less intense tornadoes are, for sure, underestimated. After the year 2000, a more careful look for reports reveals the existence of some weak tornadoes. Tornadoes occur mainly from October to January in association with strong cold fronts or line squalls. Most cases were in association with deep extratropical cyclones west of Portugal, when there was a moist and warm south–west strong to gale-force flow and a generalised severe weather over the country. Some cases happened in a very unstable westerly flow. There are also records on summer tornadoes, developing from strong thunderstorm cells. Often, such thunderstorms are mesoscale convective systems resulting from strong heating of the centre of the Iberian Peninsula.

Phase-Correcting Data Assimilation and Application to Storm-Scale Numerical Weather Prediction. Part II: Application to a Severe Storm Outbreak

Abstract A scheme to correct phase errors in numerical model forecasts using Doppler radar, radiosonde, profiler, and surface data is demonstrated to improve forecasts in a complex severe thunderstorm situation. The technique is designed to directly address forecast phase errors or initial position errors as part of a data assimilation strategy. In the demonstration the phase error correction is applied near the time of initial cell development and the forecast results are compared to the uncorrected forecast and forecasts made using an analysis created at the time of the observations. Forecasts are verified qualitatively for the position of thunderstorm cells and quantitatively for accumulated precipitation. It is shown that the scheme can successfully correct errors in thunderstorm locations and it has a positive influence on the subsequent forecast. The advantage of the phase correction over the control lasts for about 3 h despite storm dissipation and regeneration, and interactions among multiple storms.

Vertical Development of Lightning Activity Observed by the LDAR System: Lightning Bubbles

Abstract In some Florida thunderstorm cells, impulsive very high frequency (VHF) radiation from lightning channels begins abruptly in a layer that is typically 3–6 km in diameter, 1–3 km tall, and initially located just above the freezing level. In 208 cases described here, 58% of the lightning bubbles ascended with a velocity 11–17 m s–1. Of the 1060 1-h periods with lightning that were examined, approximately 10% had one or more ascending concentrations of lightning activity. Often in summer, as one region ascended, a new lightning bubble would abruptly begin near the freezing level. This subsequent region would be horizontally displaced 1–2 km from the starting point of the previous region. In winter, no more than one ascending region was seen in any one storm. A detailed examination of the structure of lightning associated with the rising layers of lightning activity indicates that these layers were composed of negative leaders, which tend to propagate through positive charge. This suggests that the r...

Lightning and thunderstorms, Part I: Observational data and model results

Lightning is an important source for nitrogen oxides (NO x ) in the atmosphere. To differentiate between the impact of lightning produced NO x and anthropogenic NO x emissions on the global atmospheric chemistry, we present a simulation of flash densities and the corresponding NO x emissions from the global climate chemistry model ECHAM4.L39(DLR)/CHEM (E39/C). The basis for a realistic simulation of flash densities is the realistic representation of deep convection in the model E39/C. This will be validated by observations from the International Satellite Cloud Climatology Project (ISCCP). We will discuss the difficulties that arise, when cloud parameters from these satellite measurements will be compared with the corresponding properties taken from a global model. The flash densities in E39/C are represented by a new lightning parameterization that connects the flash frequency of a thunderstorm with the convective air mass transport within the thunderstorm cell. This property is a reasonable and physically based indicator for lightning within a deep convective cloud. The number of convective events is simulated realistically by E39/C. The simulated heights of convective cloud tops are consistent with the observations. However, in midlatitudes over Europe, the simulated cloud top heights seem to be underestimated. The flash densities show a good agreement with the OTD observations, although the ratio of flash densities over land and over the oceans seems to be underestimated. In midlatitudes over Europe, the simulated flash densities are too low compared to the observations, this can be explained through the shortcomings of the convection parameterization. The simulated NO x emissions show maxima in the tropics and in the midlatitudes, being separated significantly from the aircraft emissions. The maximum values of lightning NO x emissions (in terms of ng(N) s -1 m -3 ), lying approximately 5 km below the tropopause, are higher than the corresponding emissions from aircrafts by a factor of three. Furthermore, the maximum aircraft emissions tend to be at higher altitude and farther north compared to the lightning NO x production.

A forecasting aspect of thundersquall over Calcutta and its parameterisation during pre-monsoon season

Severe thunderstorms accompanied by squalls are the most hazardous weather phenomena during pre-monsoon season in north-eastern region of India. An attempt has been made in this paper to study some parameters for forecasting thundersqualls over Calcutta (Airport) during pre-monsoon season. Parameterisation of thermodynamic components alongwith the synoptic support during thundersqualls over Calcutta has been discussed here. A forecasting aspect for propagation speed of thunderstorm cell at Calcutta in pre-monsoon season has been examined with respect to radar-echo positions, mid-level winds and convective available potential energy (CAPE). Occurrences of multiple thundersqualls over Calcutta Airport within a few hours’ interval have been discussed and examined through hodograph analysis, radar observations and synoptic situations.

A Case Study of Severe Storm Development along a Dryline within a Synoptically Active Environment. Part II: Multiple Boundaries and Convective Initiation

Abstract A dryline that occurred on 16 May 1991 within a synoptically active environment is examined in detail using research aircraft, radar, surface, satellite, and upper air observations. The work focuses on multiple boundaries in the dryline environment and initiation of tornadic storms in two along-line areas. Aircraft measurements in the boundary layer reveal that both the east–west extent of moisture gradients and the number of regions containing large moisture gradients vary in the along-dryline direction. Aircraft penetrations of thinlines observed in clear air return from radar reveal that all thinlines are associated with convergence and a moisture gradient, and that more distinct thinlines are associated with stronger convergence. However, significant moisture gradients are not always associated with either thinlines or convergent signatures. Convective clouds on this day formed at the dryline rather than significantly east of the dryline. The three thunderstorm cells that occurred in east-cen...

Electrical discharge from a thundercloud top to the lower ionosphere.

For over a century, numerous undocumented reports have appeared about unusual large-scale luminous phenomena above thunderclouds and, more than 80 years ago, it was suggested that an electrical discharge could bridge the gap between a thundercloud and the upper atmosphere. Since then, two classes of vertically extensive optical flashes above thunderclouds have been identified-sprites and blue jets. Sprites initiate near the base of the ionosphere, develop very rapidly downwards at speeds which can exceed 107 m s-1 (ref. 15), and assume many different geometrical forms. In contrast, blue jets develop upwards from cloud tops at speeds of the order of 105 m s-1 and are characterized by a blue conical shape. But no experimental data related to sprites or blue jets have been reported which conclusively indicate that they establish a direct path of electrical contact between a thundercloud and the lower ionosphere. Here we report a video recording of a blue jet propagating upwards from a thundercloud to an altitude of about 70 km, taken at the Arecibo Observatory, Puerto Rico. Above an altitude of 42 km-normally the upper limit for blue jets and the lower terminal altitude for sprites-the flash exhibited some features normally observed in sprites. As we observed this phenomenon above a relatively small thunderstorm cell, we speculate that it may be common and therefore represent an unaccounted for component of the global electric circuit.