Newsgroups: lter.ced Path: LTERnet!news From: Bruce Hayden Subject: CED 3.6/7 Part II Message-ID: <1994Jun23.135626.7073@lternet.washington.edu> Sender: news@lternet.washington.edu Organization: Long Term Ecological Research Date: Thu, 23 Jun 1994 13:20:43 GMT CED 3.6 and 3.7 cont. ***************************************************************** ***************************************************************** *** *** *** *** *** NEARSIGHTED IN KANSAS *** *** *** *** *** ***************************************************************** ***************************************************************** Counting the number of days when your airport is within ear-shot of thunder does not tell much about the spatial variation in thunderstorms unless you have lots and lots of airports. With the historical records of radar that we get not only a record of where there were thunderstorms but a measure of their vigor! Pulses of radar are set out and they bump into rain drops and get reflected back to the receiver. NOAA takes its radar screen and puts it through a "Video Integrator and Processor" that is government talk for a VIP. There are 6 levels of VIP. The bigger the drop the more intense the storm that was making the drops and the higher the rainfall rate. Here is the classification used by our friends at NOAA. _____________________________________________________________________ VIP Signal Interpretation Precipitation Rate (in/hr) _____________________________________________________________________ 1 Light rain or snow less than 0.2 2 Moderate rain or snow 0.2 to 1.1 3 Heavy rain or snow 1.1 to 2.2 thunderstorms 4 Very heavy thunderstorms 2.2 to 4.5 5 Intense thunderstorms 4.5 to 7.1 6 Extreme thunderstorms more than 7.1 ____________________________________________________________________ Using 5 years of hourly VIP data for Kansas in 22 km grid cells for 4, 5 and 6 level VIP signals, folks here at Virginia totaled up the number of hours. We used radar catagories of very heavy or more intense thunderstorms recorded at some time during each hour as our metric. Now you might ask why we picked on Kansas. Well we did the same study in Florida and Virginia. We found that thunderstorms are not randomly distributed over the landscape. There were bulls-eyes: hot spots with many, many hours of big time thunderstorms. There were hours-countour-pits where the most-fun thunderstorms were rare. These thunderstorm frequency maxima and minima were on the order of 60 km in diameter and were geographically specific. Now, had you quizzed me before this study I would have said all areas are equally likely to get thunderstorms even though my neighbor farmer would have given a chuckle over my egg-head-answer. Well, Florida has oceans and islands and wonderful sea breezes that can get a thunderstorm going. Virginia has immobile mountains, a bay, a peninsula, lagoons, barrier islands and an ocean so why not some spatial explictness in thunderstorms. Our solution was to pick a billiard-table shaped state. We picked Kansas. When I did this study, before I knew of Konza Prairie, my only experience with Kansas was Rt. 36 in the early 1960s. I thought when you had seen one square mile you had effectively seen them all. Well, the thunderstorm-hours maxima and minima were -- you guessed it -- bulls eyes! Kansas severe thunderstorm bulls-eyes were on the order of 130 miles in diameter. Kansas thunderstorm, compared to those of the Old Dominion, are much bigger in diameter and usually in height as well. ________________________________=======_____ | =========== ============== | Kansas | =========== === =====MIN===== | Annual | ====MIN=== ===== ============= | Thunderstorm | ================ =========== | Hours |::::::: ======== ===== | |::::::::: :::::::::: | | MAX:::::::::::::: :::::::::::::::::::: | |::::::::::::: === ::::::::::::::::::::: | |::::::: ========= :::::::::::MAX::::::::::| | =========== ::::::::::::::::::::::::| | ========== :::::::::::::::: | | =====MIN== | |______________________________________________| The thunderstorm-hours maximum in the SE corner of Kansas totals 333 hours per year with rain that falls at a rate of at least 2.2 inches per hour. Well, that isn't more than 700 inches???? No, it is not required that in each hour that a thunderstorm rain for the entire hour. The radar takes a "snapshot" one time per hour. It might only rain in excess of 2.2 inches for 5 or ten minutes but could be longer! So you cant get rainfall totals from the radar as we know it today. The minimum in the south central area in the northeast corner are 141 and 210 hours per year, respectively. The minimum in the NW corner is only 104 hours of sever thunderstorm per year. The maximum in the west is 245 severe thunderstorm hours per year. The real question is why do these thunderstorm hot-spots and thunderstorm wimp-spots occur. There is nothing in the structure of the atmosphere that would give rise to this pattern. It must be the surface that and its fluxes of mass and energy (sensible and latent) and surface roughness that we should look to for causal culprits! Roger Pielke has run his thunderstorm generator model for the Konza area and has concluded that the soil moisture, roughness, and the flux of latent and sensible heat is coupled to the time of day of onset of thunderstorms and just how big they grow-up to be. So uniform Kansas is not so uniform and boring when it comes to the haves and have nots of thunderstorm getters. This view is based on radar records for 22 mile squares across Kansas. It is now possible to get 1 mile resolution. Not many years of data yet but the day is coming when we will know the hour by hour intensity of thunderstorm and rain fall rates. Years of saving this data and doing the analysis makes one dream of super computers and parallel processing. ***************************************************************** ***************************************************************** *** *** *** *** *** PEALS, CLAPS, ROLLS & RUMBLES *** *** *** *** *** ***************************************************************** ***************************************************************** When you talk about thunder you are permitted to use the terms peals, claps, rolls and rumbles to describe your observations. However, those in-the-know know that peals and rolls are kinds of rumbles and talk only of claps and rumbles. The clap comes first and is followed by the rumbles. Timing claps and rumbles tells you lots about the lightning stroke. Count the seconds between the flash and the clap and multiply by 1100 feet and you get the distance between you and the lightning strike. With luck your counting will get past milliseconds and into seconds. Five seconds puts the lightning a mile away. The rumble is generated along the entire length of the shaft of the lightning. A 20 second rumble indicates a channel of about 4 miles. Now, you know what it means to have a clap 10 seconds after the flash followed by 20 seconds of rumble. Most of the sound energy is around 50 hertz (1 Hertz = 1 cycle per second). When you get a hearing test your are checked over the range 125 to 10,000 Hertz. How well you hear thunderstorms is not usually the subject of interest to your Beltone sales person. ***************************************************************** ***************************************************************** *** *** *** *** *** LONG DISTANCE SOUNDS *** *** *** *** *** ***************************************************************** ***************************************************************** When you have thunderstorms about the turbulence of the atmosphere is great and the distance that sound travels is limited by such turbulence to about 15 miles. 15 miles with the speed of sound at 1100 feet per second means a wait of 75 seconds between flash and sound. When a thunderstorm is far away you generally don't hear the clap (mostly higher frequency sound) because the higher the frequency the faster the turbulence attenuates the sound. Rumbles travel much farther than the clap. A flash and rumble means the strike was in somebody else's back yard. Who would want a flute for a fog horn? Not safety conscious people like you and me. Elephants communicate with very low frequency sound, the kind that goes a fair distance. If there is little or no turbulence, sound can go much farther. This happens when the air is nicely layered. Like near sundown when the sky is beautiful and well layered and after a night of nocturnal cooling and surface temperature inversions. If you are an elephant with hormonal-needs of communication, mate calling is favored at such times. With ducting of sound in such stratified atmospheres the call can easily go tens of miles. While I have a good colleague at Virginia who is into elephant communication, my experience comes from the 4th of July. Crozet, a village about 2 miles north of my home, has a firemans-fund-raising-fair each year. Just after sundown and waiting darkness for the fireworks you can hear the conversation of fair-goers at least from the base and baritone types. This year I am going to check-out and see if the high-frequency, squeaky voice types can be heard from my lawn chair. Who would you want to yell for help if you got in a jam? ***************************************************************** ***************************************************************** *** *** *** *** *** THUNDER *** *** *** *** *** ***************************************************************** ***************************************************************** Most of the sound of thunder comes from the return stroke of lightning. The energy involved is 10,000 joules per meter of lightening channel. In the channel itself there is molecular dissociation, ionization, excitation, kinetic energy production and radiation -- all in 10 to 20 micro-seconds. Temperatures in the plasma reach 30,000 K. Plasma pressure reaches 10 atmosphere (10,130 mb). Outside the channel air pressure is about 1 atmosphere (1013 mb). The mass in the channel expands at supersonic velocities. A Sonic boom results as this kinetic energy decays into sub-sonic sound energy. ***************************************************************** ***************************************************************** *** *** *** *** *** BEN FRANKLIN *** *** *** *** *** ***************************************************************** ***************************************************************** Ben Franklin is famous for his inventions. The lightning rod is his! It hasn't been improved since his day. If your spouse is approached by a sales person of the huckster type who wants to put a radioactive substance at the tips of each of your lightening rods under the theory that the bit of ionization there will better attract the lightning, said spouse should say, "Thanks but no thanks." The ionization that happens naturally at the sharp tip of metal is several orders of magnitude greater than offered by a radioactive lightning-rod-tip. A good rasp type file would sharpen your lightning-rod-tips and up the ionization. I wonder how Ben new to put a tip rather than a ball on his lighning rod. Ben is one of my heros. Anyone who could invent the lightning rod and discover the Gulf Stream in one career would be fun to have at an LTER site.