WO1990014605A1

WO1990014605A1 - Microburst/windshear warning system

Info

Publication number: WO1990014605A1
Application number: PCT/US1990/001965
Authority: WO
Inventors: Ralph J. Markson; Bruce E. Anderson
Original assignee: Airborne Research Associates, Inc.
Priority date: 1989-05-17
Filing date: 1990-04-11
Publication date: 1990-11-29
Also published as: AU5540090A; US4996473A

Abstract

A system for predicting the occurrence of microburst/windshear comprising at least one sensor (520) for receiving lightning produced signals, a processor (210) for processing those received signals to produce data and generate a warning (224) when the processed data indicates that a microburst/windshear is about to occur.

Description

__^•]___. P T/US90/0195

I4ICR0BURST/ΕNDSHEAR WARNING SYSTEM

This invention relates to the prediction of icrobursts and windshear which can accompany thunderstorms.

Background One of the more spectacular of atmospheric events is a thunderstorm. In a thundercloud, charges become separated until the potential difference within the cloud or between the cloud and ground exceeds 100 million volts. When the potentials become that high, a relatively low current discharge occurs, called a leader. The leader ionizes a small irregular path of air in a series of rapid steps. The leader provides the higher conductivity path that the return stroke, the luminous discharge usually referred to as lightning, will travel during a discharge.

Each lightning flash may actually be composed of several strokes. Each stroke results in a peak current flow of typically more than 20,000 amps. The passage of this amount of current fully ionizes the air in the lightning channel and results in the production of light and radio frequency (RF) electromagnetic waves. The RF radiation produced in a storm is both vertically and horizontally polarized and has a wide-band frequency distribution. Not all lightning occurs between earth and ground. The majority of lightning is intra-cloud or between clouds. Interferometric measurements have shown that the majority of discharges take place within a cloud. These discharges are characterized by hundreds of RF point sources which propagate horizontally within the cloud and only infrequently turn toward earth to become cloud to ground discharges. Most of the energy in RF emissions from intra-cloud discharges is in the high, very high and ultra high frequencies while most of the energy in cloud to ground discharges is in the low and very low frequencies.

Although the mechanism by which electric charges are separated in a thundercloud is not completely understood, it is known that the charge separation is accompanied by vertical movements of air. During the initial formation of the thundercloud there is an upward movement of the air mass, an updraft, from the bottom to the top of the developing cloud. The updraft is presumed to contribute to the separation of charge by carrying charged ice particles into the updraft region. These ice particles absorb moisture from the air and grow until they are too large to be supported. When that happens, they begin to fall, and continue to grow by sweeping smaller particles from the air column.

As the larger particles fall, they entrain nearby air into a downdraft, which pulls dryer air from outside the falling air column into the column. The dry air causes the ice particles to sublimate, which results in the cooling of the falling air column. As the air cools, it becomes denser and falls faster. A considerable mass of solid and liquid water also may be in the downdraft. If the falling column of air passes through the

0°C isotherm toward warmer temperature, the ice particles will melt. The phase change from ice to water will further cool the air, resulting in the additional loss of buoyancy. This loss further increases the air column's downward acceleration. This downward moving column of air, typically .4-4 km in diameter and moving in excess of 3-4 m/sec, is called a microburst.

When the microburst approaches the ground, the column of air is deflected and moves along the earth's surface. This can be similar to the way water from a hose sprays radially when the hose is pointed at the ground. Because of this divergence of the air column near the ground, the direction of the air flow near the ground level will appear to vary as one moves vertically over a relatively short distance. This abrupt change in wind velocity with altitude is called windshear.

Both microbursts and windshear are of more than academic interest because of the dangers they pose to aircraft. If an aircraft, taking off or landing, passes into a microburst, it is exposed to a downward acceleration at a time when there may be insufficient altitude for the pilot to avoid crashing.

Windshear poses a similar hazard. The lift provided by an aircraft wing is determined by the velocity of air passing across the wing. The velocity of the air passing over the wing is in turn determined by the relative velocity of the aircraft through the air. If the relative velocity decreases past a critical value, the air begins to separate from the wing surface and the aircraft loses the lift necessary to remain airborne.

This loss of lift is termed stalling. An aircraft which is taking off or landing is operating just above the velocity at which it stalls. If the wind direction is suddenly reversed, the aircraft may find that its relative airspeed, which was greater than its stall velocity, is now below its stall velocity, and that it has insufficient lift to remain airborne.

This can happen when an aircraft takes off or lands within a region of wind shear. Although the wind velocity may initially be such that the relative airspeed is greater than the stall speed of the aircraft, just a short vertical distance away, the aircraft may move into a region where the wind direction reverses, causing the wind speed over the wing to fall below stall velocity. Since this usually happens near the ground, the pilot may not be able to increase the speed of the aircraft quickly enough to regain lift before the aircraft loses what little altitude it has.

Particularly susceptible to these problems are the large jet aircraft used by the airline industry. Because these airplanes are so large, and because a jet engine requires a substantial amount of time to build up trust; a pilot may not accelerate the airplane quickly enough to avoid crashing if the plane stalls because of windshear or is forced to the ground because of microburst downdrafts and mass loading of the airframe. Over the last few years several airline disasters have been attributed to windshear or microbursts.

Several systems have been invented to alert ground personnel of the existence of potentially dangerous wind variations that would be hazardous to aircrafts which are landing or taking off. One of the systems consists of a two dimensional horizontal array of wind direction and velocity indicators located on the ground at an airport. When a microburst occurs, different sensors in the array indicate a different wind direction and speed at the same time. Although it is possible to infer windshear with this system, only a relatively small region can be monitored. Further, the system can only indicate that a microburst is occuring and can not predict when or where microbursts or windshear will occur.

In an effort to increase the size of the region monitored for windshear and expand coverage into another dimension (height) , Doppler radar is used. Doppler radar measures the velocity component of particles of dust or rain in the direction toward or away from the radar antenna. The principle is that under windshear, a small region of space will appear to have particles moving toward or away from the antenna at different velocities as a function of height. Unfortunately, nothing of the particles moving perpendicular to the radar beam can be determined. Therefore, microburst downdrafts cannot be measured by Doppler radar scanning close to the horizontal plane, which is its normal mode of operation. Doppler radar will only detect microbursts if they are close by, and then only if the radar antenna is pointed upward. Doppler radar can also detect windshear after the microburst air turns horizontal near the ground. However, if there are no particles, such as when the rain evaporated below cloudbase in the "dry" thunderstorms in clean air which occur in parts of the country, there may be no windshear detected. Again, Doppler radar can only be used to indicate the presence of windshear, not predict it's occurence. Other devices have been developed to make use of the electrical discharge which occurs to detect the presence of thunderstorm activity. The devices do not measure microbursts and windshear directly but simply warn of the presence of thunderstorms and therefore the possibility of windshear. U.S. Patent No. 4,023,408 discloses a device which measures the direction to an intra-cloud discharge and estimates its distance by determining the intensity of the strength of the RF signal generated by the discharge. The assumption is made that the higher the signal strength, the closer the discharge. This device has inherent inaccuracy because it will regard a close weak discharge as being further away then a strong distant discharge.

Another device (U.S. Patent No. 4,672,305) measures the ratio of the electric to magnetic field of the discharge to determine the distance to the discharge if the discharge is within 20 nautical miles, and the ratio of the magnetic fields at two frequencies if the discharge is greater than 20 nautical miles from the receiver. Again this device can only estimate the distance of the lightning flash. Both these lightning mapping systems detect intra-cloud discharges, but because of the elongated nature of the radiator and variable polarization of the discharges, they cannot resolve the direction to the discharge with much accuracy.

Lightning interferometers are capable of resolving the intra-cloud lightning discharge into a series of radiators. Such devices allow the electrical discharge within the cloud to be mapped with high resolution and a detailed description of the lightning discharge to be obtained.

None of these devices actually measures or predicts microbursts or windshear. The present invention provides a warning to a high degree of certainty that a microburst is about to occur, allowing pilots ample time to make an appropriate response.

Summary of the Invention The invention disclosed herein involves a system of predicting microbursts and windshear based upon the reception of the. signals generated by lightning. A plurality of sensors monitor the VLF, VHF, UHF or visible bands of the spectrum, and relay the data to a processor which calculates the location of the lightning, the frequency of the discharges, the rate of increase in the frequency of discharge, and the aerial density of the discharges. When the frequency and the rate of change of frequency exceed a threshold level for a given area, a microburst is imminent in that area. The present invention provides the capability of predicting with near certainty the occurence of a microburst from the signals from a thundercloud and not simply reporting that a burst is occurring. Brief Description of the Drawing The drawing is briefly described as follows. Fig. 1 is a graph indicating the relationship between microbursts, total lightning, and intra-cloud lightning;

Fig. 2 is a block diagram of generalized embodiment of the invention;

Fig. 3 is a block diagram of an embodiment of the invention using electrostatic sensors; Fig. 4 is a block diagram of an embodiment of the invention with airborne VHF or UHF receivers and a transponder downlink;

Fig. 5 is a block diagram of an embodiment of an invention using lightning interferometer; Fig. 6(a) is a flow chart of the main algorithm used to predict microbursts; Fig. 6(b) - 6(f) are flow charts of the subroutines called by the main routine shown in Fig 6(a); and

Fig. 7 is the case table used by the algorithm for setting the watch or warning flags.

Description of the Preferred Embodiments Fig. 1 graphically illustrates the relationship between total lightning frequency (shown as a solid line) 10, cloud-to-ground lightning frequency (shown in cross- hatch) 12, and differential radial air mass velocity 14 (shown as a broken line) which is associated with microburst activity. (Intracloud Lightning As A Precursor To Thunderstorm Microbursts - E.R. Williams, and R.E. Orville, Proc. 1988 Int. Aerospace and Ground Conf. on Lightning and Static Electricity. 1988, pp. 454- 459) . As can be seen from this graph, the microburst, as detected by the peak radial velocity 16 followed immediately after a dramatic increase of intra-cloud discharges as shown by the peak in the total lightning frequency 18 and no increase in the cloud-to-ground lightning frequency 20. It can be inferred that the intra-cloud lightning activity is a more accurate prediction of microburst formation than is the cloud-to- ground activity or total discharge activity. To predict microbursts, it is necessary to measure the discharge frequency and location and indicate that a microburst is imminent and signal an alarm when the discharge frequency and its time derivative reaches a given threshold within a region of limited area.

A system for predicting microbursts is shown in Fig. 2. A data processing system 210 collects data from a series of sensors 212 216, and 220 which either have local processing capabilities 212, 216 and transmit to the central data processing system analyzed-data concerning the frequency of discharges and the location of the storm, or do not have local processing capabilities 220 and which transmit to the processor 210 raw information concerning the detection of a discharge and its location. If the sensors are airborne 212 it is possible either to transmit this data over radio links dedicated to such data collection or using the transponder down-link 214 which is currently used by aircraft to communicate aircraft data to the ground. Ground based sensors 216, 220 can either communicate over dedicated lines 218 or through radio, microwave or laser links 222.

Considering each of the system components separately, many types of sensors are suitable for use in this system. An example of an array of sensors which can be used with this system are shown in Fig. 3. The data processing system 210 is connected to sensor array 310 through communications links 218. The sensor array 310 is a two-dimensional array of electrostatic potential (corona point) detectors 308 as are described in a co- pending patent application, serial No. 281,842 filed December 8, 1988 herein incorporated by reference. Each detector 308 measures the fluctuations in the electrostatic potential and reports the potential measurement to the central data processing system 210. Lightning discharges manifest themselves as a discontinuity in the electrostatic potential. From this data the data processing system 210 can determine the frequency of discharge. Additionally, since the detectors closest 313 to the discharge 305 will experience the strongest signal, the location of the discharge can be determined.

This array with local processor is then linked to the central data processing unit 210 to provide data concerning the location of the predicted microburst. To improve the accuracy of microburst prediction one can distinguish the rate of discharge for intra-cloud lightning flashes from cloud-to-ground lightning. This can be done simply by measuring only the VHF/UHF radio frequency emissions which come predominently from intra- cloud lightning. Alternatively it is possible to measure the ratio of VHF/UHF to VLF energy which is much larger for intracloud discharges. The use of VHF/UHF emissions also allows the individual segments of the intra-cloud lightning to be resolved. The microsecond resolution of interferometers or time of arrival systems makes possible resolution of much less than 1 km, the scale of microbursts. This is in contrast to the use of VLF RF detection systems with msec resolution and which do not provide spatial resolution within a stroke. Such a system resolves a stroke, which can propagate many km horizontally, as a single radiator. VLF detection therefore will simply determine some location along the stroke as being the source of the radiation. This location will generally be the initial source of the radiation; the region with largest electric fields. This high electric field region is where the charge is separated within the updraft phase.

The VΗF/UHF sensors may be located on the ground or in an aircraft. An example of an VHF/UHF airborne system 212 is shown in Fig. 4. A VHF or UHF receiver 418 receives VHF or UHF signals from a lightning discharge 305, through a crossed-loop directional antenna 416. The crossed loop antenna 416 provides the direction information, while the difference in the arrival times of the signal traveling from the discharge 305 to the antenna 416 directly by path 412 and that traveling from the discharge 305 to the antenna 416 after reflecting 414 from the ground 410 provides the distance information. The direction and distance information from the VHF or UHF receiver is processed by a local data processor 422 prior to being incorporated in the information being transmitted 214 by the aircraft's transponder 420. This information is received by the central data processing system 210 which then, knowing the position of the storm relative to the aircraft and knowing the position of the aircraft relative to the central data processing system's ground location can determine the location and frequency of lightning discharges relative to it's ground location. The aircraft's location relative to the ground can either be determined by using ground radar or by receiving the aircraft's own navigation (e.g. loran) and altitude information. Although it is not necessary to use the aircraft's transponder to transmit the data to the ground, the advantage of using a transponder is that this communications channel already is in operation on all commercial and many non-commercial flights. The use of routine commercial flights to gather data has the advantage that the large number of commercial flights . makes it possible to predict microburst and thunderstorm activity over a large portion of the country, particularly near airports where aircraft density maximizes and windshear is a problem. Another embodiment of the invention is shown in Fig. 5. In this embodiment a lightning interferometer 510, consisting of at least two VHF or UHF receivers 418 and antennas 520, separated by a distance receive radiation from a lightning discharge 305 by two paths 522 and 524. The difference in the path lengths 522 and 524 generates an interference pattern when the signals are combined in a local data processor 422. From the interference information, direction and distance, to the discharge can be determined. This information is then transmitted to the central data processing system 210 over the communications link 212. This system is capable of resolving the location of each segment of intra-cloud lightning and thereby provide very accurate location information. Once the sensors have collected and transmitted the information, the next component of the system, the central data processor, receives the data and performs a series of calculations. The purpose of the calculations is to locate and quantify the density of discharges within a given region and determine the time rate of change of activity within the same region.

Specifically, the region of concern is the area whose center is at the center of the thunderstorm and whose radius extends to a distance equal to the radius of a typical thunderstorm plus a distance equal to the uncertainty in the location of the storm (i.e. the accuracy of the detector) . Within this region the number of discharges per unit time is calculated as is the time rate of increase. When the flash rate reaches five flashes per minute, and the increase in rate is one flash per minute per minute, over the previous five minutes within a region of the storm, an alarm is given that indicates microburst is about to occur.

Fig. 6(a) is a flow chart of the main algorithm for performing this calculation. Overall, the algorithm determines whether the sensor has detected lightning, and if it has, the algorithm calculates the position of the lightning, the flash rate and the density. Then, depending upon the results of those calculations, evaluates the threat and produces a microburst watch or warning. To do this, the algorithm performs the following steps.

The system is initialized 612 using windspeed and wind direction at the -25°C isotherm 610. These parameters will be used to chart the future course of the storm. The electrical signals from the detectors 614 are processed 616 to determine if lightning is present 620. If lightning is present, the data from the detectors are stored for later use 618 and the position of the lightning 624 is determined.

If no lightning is present, indicators (or flags) , about which more will be said, are checked to determine if windshear alert is in effect 622. If no alert is in effect, a new lightning position is calculated 626 using the windspeed and direction of the storm. A new total flash rate 630, which is decreasing because of the lack of lightning flashes, is calculated and the display is updated 632. The system then loops to process more data from the detectors 616. If the wind shear alert indicator is set, the lightning position is calculated

624 again using the windspeed and direction of the storm.

In both the case where the lightning is present and the case where a windshear alert is in effect, the next step is to compute the total flash rate 628. Again the flags are checked to determine if a windshear watch or warning is in effect 634. If neither is in effect, a determination as to whether a thunderstorm exists is made 636. If no storm exists, the display is simply updated 632 and the loop is recommenced with the system processing data from the detector 616.

However, if a windshear watch or warning is in effect or if a thunderstorm is shown to exist, the flash density is computed 638. The windshear watch or warning flags are again checked 640 and if neither is set, the flash density is checked to determine if the density iε more than 1 flash per unit area 642. If the density is less than 1 flash per unit area, the display is updated 632 and again the loop repeated.

If either a windshear watch or warning is in effect, or if the flash density is more than 1 flash per unit area, the flash rates and changes in the flash rates are computed in the dense activity areas 644, about which more will be said. The windshear alert flag is checked 646 and, if set, a determination is made as to whether the threat continues 648, or if no flag is set, a determination is made as to the existence of a threat 650. From this, whether or not a windshear hazard exists 652 is determined.

If no hazard exists, the conditions are checked to ascertain if pre-windshear conditions 654 are present. If so, a watch flag is set 662, the display updated 632 and the loop completed. If the windshear conditions do not exist, the display is simply updated 632 and the loop completed. If a windshear hazard exists, the projected path of the activity is computed 656. The previous movement of the activity is also computed 658 and depending upon these results, the windshear warning flag 660 may be set. The display is then updated 632 and the loop repeated. Having shown the main algorithm, the major components will now be discussed.

In order to calculate the lightning position, (Fig. 6(a), 624 and 626,) the algorithm shown in Fig. 6(b) is performed. First, it is determined if the sensor is moving 664, that is, for example if the sensor is airborne. If the sensor is mobile, the direction and speed of the sensor 678 are used to determine the sensor's heading and position 668. From this, the lightning position is translated 670 using the wind vector information 610 (Fig. 6a) . If the sensor is not mobile, the lightning position is translated 666 using the wind vector information alone.

The data is sorted according to the amount of time since the flash 672. The most recent five minutes of data is saved 674 for later use. The translated positions of activity for the most recent 20 minutes is also saved 676.

Fig. 6(c) depicts the steps in calculating flash density 638 (Fig. 6(a)). The translated positions for the last five minutes, 672 (Fig. 6(b)), are examined 680 and the data from the last minute extracted 682. From this data, the number of flashes within a radius x of each flash is calculated 684. From this information, a determination as to whether or not an activity center exists 686. If there is no activity center, the subroutine simply terminates and the main program continues.

If a center does exist, flashes are selected which have more than one flash near them and a check for overlap is performed 688. The average position of the ensemble is computed 690 as is the number of flashes within x of this average position 694. The average position is recomputed 696 and a determination is made as to whether or not this position converges 698. If there is no convergence, the number of flashes within x at the new average position is computed 694 and the loop repeated. If there is convergence the center of activity is stored 700, as is the number of flashes and the standard deviation (σ) from "the center 692.

To compute the flash rates and the rate change in dense activity areas 644 (Fig. 6(a)) the algorithm shown in Fig. 6(d), is performed. Again, the translated data for the previous five minutes 674 (Fig. 6(b)) is examined 702 and the activity centroids calculated 704. The flashes are then sorted into one minute time bins 706 and the number of flashes within an x radius of each centroid is calculated for the previous five minutes 70S. A five minute average flash rate 710 for each centroid is calculated 710 as is the average rate of change for the past five minutes 712. - These results are then stored 714.

Fig. 6(e) dicloses the steps in determining the threat of windshear. First, the centroid of activity, flash rate and curvature is determined for each activity center and the warning flags are reset 716. If the flash rate is greater than or equal to five per minute, 718, a flag, in this embodiment flag-1, is set 720. Next, it is determined whether the flash rate is greater than or equal to three flashes per minute 722. If yes, a second flag, in this embodiment flag-2, is set 724. If the activity is increasing 726, a third flag, flag-3 in this embodiment, is set 728.

Next, if the rate of increase is greater than one per minute per minute 730, a forth flag, flag-4 in this embodiment, is set 732. Optionally, depending upon the sensor's ability to distinguish cloud to ground (CG) and intracloud (IC) flashes, the CG/IC ratio can be calculated 724 and if the ratio is less than one 736, a fifth flag, flag-5 in this embodiment, is set 738. From the various combination of flags, as shown in Fig. 7, the case can be determined 740. If the case is one 742, the system warning flag is set 744. If the case is two 746 the system watch flag is set 748. If neither of the cases are present, the .algorithm simply exits and returns control to the main program.

Fig. 6(f) shows the steps in evaluating the threat (648 Fig. 6(c)). Each centroid is translated 750 and if the centroid is still within range 752, the number of flashes within a radius X of each centroid for the previous five minutes 754, is calculated. If more than one minute has elapsed 752 since the last flash was near the centroid, the warning flag 750 is cleared. If two or more minutes have passed since a flash was near the centroid 760 then the warning flag is cleared 762 and the watch flag 764 is set. Otherwise, the warning flag 766 is reasserted and a determination made as to whether a new hazard area exists.

Having shown the preferred embodiment, those skilled in the art will realize many variations are possible which will still be within the scope and spirit of the claimed invention. Therefore, it is the intention to limit the invention only as indicated by the scope of the claims. What is claimed is:

Claims

1. A system for predicting the occurrence of microbursts comprising: a. a plurality of sensors for receiving lightning produced signals from a thunderstorm; b. a central processor for processing data; c. a communications link for transmitting data based upon signals produced by a thunderstorm from the sensors to the central processor; d. a warning device for warning a user when the processed data predicts the occurrence of a microburst.

2. The system of claim 1 wherein the sensors measure the electrostatic potential.

3. The system of claim 1 wherein the sensors detect electromagnetic emissions from the lightning discharge.

4. The system of claim 3 wherein the sensors detect VHF radiation.

5. The system of claim 3 wherein the sensors detect UHF radiation.

6. The system of claim 3 wherein the sensors detect visible light radiation.

7. The system of claim 1 wherein the sensors are airborne.

8. The system of claim 7 wherein the communications link is part of a transponder.

9. The system of claim 1 wherein the sensors are ground based.

10. The system of claim 7 or 9 wherein the communications link is a dedicated radio channel.

11. The system of claim 1 wherein the frequency and directional information of the lightning is processed by a local processor connected to said sensors prior to being communicated over said communications link to the central data processor.

12. A system for predicting the occurrence of microbursts comprising: a. a plurality of sensors for receiving signals produced by lightning; b. a central processor for predicting the occurence of a microburst, said processor comprising i. a storm location device for determining the direction and speed of a lightning centroid; i.i. a flash location device for determining the rate of lightning flashes, the change in the rate of lightning flashes and the position of the lightning flashes relative to a lightning centroid; iii. a hazard analyzing device for determining the threat due to a thunderstorm by examining the rate of lightning flashes, the change in the rate of lightning flashes and the position of the lightning flashes; and c. a communication link for transmitting data from said sensors to said central processor.

13. A system for predicting the occurrence of microbursts comprising: a sensor for receiving signals produced by lightning; a processor for predicting the occurrence of a microburst, said processor adapted to execute: i. an algorithm to determine the location of the lightning centroid; ii. an algorithm to determine the direction and speed of the lightning centroid; iii. an algorithm to determine the location of a lightning flash relative to the lightning centroid; iv. an algorithm to determine the rate of lightning flashes; v. an algorithm to determine the change in the rate of lightning flashes; vi. an algorithm to determine the windshear hazard based upon the rate, change in rate, and position of lightning flashes; vii. an algorithm for displaying the results of the calculations of the algorithm to determine windshear hazard; and a communications link connecting said processor and said sensor.

14. A system for predicting the occurrence of microbursts comprising: a sensor for receiving signals produced by lightning; a processor for predicting the occurrence of a microburst, said processor comprising: i. an apparatus to determine the location of the lighting centroid; ii. an apparatus to determine the direction and speed of the lightning centroid; iii. an apparatus to determine the location of a lightning flash relative to the lightning centroid; iv. an apparatus to determine the rate of lightning flashes; v. an apparatus to determine the change in the rate of lightning flashes; -- vi. an apparatus to determine the windshear hazard based upon the rate, change in rate, and position of lightning flashes; and vii. an apparatus for displaying the results of the calculations of the algorithm to determine windshear hazard; and a communications link connecting said processor and said sensor.

15. A method for predicting windshear hazard comprising the steps of: receiving signals produced by lightning; determining the location of the lightning centroid from said received signals; determining the direction and speed of said lightning centroid; determining the rate of lightning flashes; determining the change in the rate of lightning flashes; determining the hazard due to windshear using the rate, change in the rate and location of lightning flashes; and displaying the results of said hazard determination.