The March-April edition of WeatherWise magazine has an interesting article in it regarding UHI (Urban Heat Island) effects of enhancing thunderstorm formation in the downwind heat plume. It Stems from this paper (PDF) published in the Bulletin of the American Meteorological Society. I saw a similar study presented in August 2007 when I attended Dr. Roger Pielke’s land use conference presented by Dr. William Cotton on the enhancements modeled in St. Louis, MO. Read that paper here
Excerpts from WeatherWise Magazine:
The Atlanta Thunderstorm Effect
by Mace Bentley, Tony Stallins and Walker Ashley
Although nearly everyone is fascinated by lightning, some of us are terrified, while others are drawn to its elusive beauty. Lightning is one of the most photogenic of all atmospheric phenomena, but also one of the least understood. For all of its beauty, lightning is a major cause of weather-related deaths in the United States and accounts for more deaths than hurricanes and tornadoes combined. Nearly 40 percent of all lightning deaths occur when a person is involved in some form of outdoor recreation.
Now, new evidence suggests that lightning and its parent thunderstorms might actually be enhanced by cities. Urban areas are literally hotbeds for producing heat and lift, two important ingredients for thunderstorm formation. At the same time, throughout the world people are continuing to migrate to cities for employment opportunities and the search for a better life. Eighty percent of the U.S. population now lives in cities. City growth has increased the amount of urbanized land cover in the United States to nearly the size of Ohio! In the United States, many of our cities in the south are growing rapidly due to their location in a more temperate climate. However, a temperate climate also means cities are more prone to thunderstorms. Could all of these factors together combine to increase risk of lightning and other thunderstorm hazards to urban communities around the world?
The Urban Heat Island
The first step in unraveling the question is to understand the interaction between the land and atmosphere. It is currently thought that several processes in this complex interaction are likely at work in altering thunderstorm distributions around cities.
The first is the urban heat island effect, perhaps the most well-known atmospheric phenomenon produced by a city. An urban heat island occurs when the city registers higher temperatures than the surrounding rural areas. Cities heat up because of all the “activity” in them. Cars, air conditioning units, idling engines, and miles of asphalt and concrete all either produce or retain heat. The most notable feature of an urban heat island is the lack of cooling during late afternoon and evening after temperatures normally reach their highest. When compared to the rural countryside, urban corridors have much less area exposed to open air and instead have many warm buildings facing each other. Less heat is lost, and higher nighttime temperatures result. After sunset, city-to-countryside temperature differences grow quickly and can reach, in some cases, more than 10°F. The greatest city-to-countryside temperature differences occur during the long, hot days of summer when daylight is maximized.
…
Caption: Radar climatology illustrating the clustering of strong thunderstorm days directly over and immediately surrounding Atlanta, Georgia.
Caption: Plot of lightning events during periods of westerly flow illustrating downwind enhancement east of Atlanta, Georgia.
The Atlanta Case
The 10-year study of lightning, rainfall, and thunderstorm activity in Atlanta in the summer months showed that enhanced thunderstorm activity was found to shift due to prevailing winds. For example, westerly winds produced a distinct increase in lightning activity east of downtown Atlanta. Evidence suggests that thunderstorms developing over the city center, as well as storms along the periphery, were being directed by the westerly winds to the east side of the city and suburbs. The Atlanta enhancement, particularly for lightning, was well developed for westerly and northwesterly winds that carried thunderstorms east and southeast of downtown. Thunderstorm enhancement can occur in all directions around downtown Atlanta, directed primarily by the prevailing wind direction.
“Pollution can alter how a thunderstorm forms”
“As water droplets collide and freeze onto hail and other ice particles, negative charges are removed from the updraft and added to the downdraft of the thunderstorm”
The rainfall and lightning characteristics of thunderstorms developing in and around Atlanta were also detected when examining radar reflectivity. Over the 10-year study, high radar reflectivity “hotspots” were persistently found along and north of downtown Atlanta and immediately east of the central business district. Towering cumulonimbus clouds containing high concentrations of water droplets and ice crystals reflect significant amounts of microwave radiation back to the radar antenna. On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location. Radar-identified thunderstorms were found to be greatest over the downtown with a general decrease moving outward from the city center. A similar pattern was found over other southern U.S. cities. It appears that the Atlanta urban heat island and associated buildings may combine to produce the downtown thunderstorm radar “hotspot,” while the urban heat island-produced circulations on the fringes of the city lead to increases in suburban thunderstorms, lightning, and rainfall.
“Radar-identified thunderstorms were found to be the greatest over the downtown”
Although less important, the terrain might also be linked to the lightning and rainfall patterns surrounding Atlanta. Winds from the northeast off the Appalachians and the focus of rainfall and lightning activity on the upwind side of Atlanta suggest that elevation changes across the metro area may interact with the urban heat island circulation and focus lightning and rainfall on the north side of the city. One explanation is that air flowing downhill from the Appalachians will be forced to rise once it encounters the buildings on the northern edge of Atlanta. This is distinct from other prevailing wind directions, where lightning activity was found to intensify over and downwind of the city center.
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Very interesting. Hot air rises, collide with cooler air, add in some water vapor cussing rain which cools down the city. So If Co2 is causing the UHI, the result is rain cooling down the city or a Negative feed back to Co2 “heat effect”.
Atlanta is also a MAJOR air hub. Jet exhaust is well known for its ability to seed unstable air and produce clouds and rain. No study of Atlanta weather can be complete without taking into account the jet activity around and especially downwind of the airport. Didn’t see any mention of that in the article.
I work in a building that is under the approach to a major runway at YYZ. The area for several blocks gets more snow than adjacent areas. I’ve never been to a summer airshow in which it didn’t cloud up and spit some rain by late afternoon when there was a lot of low level jet demos.
@Tom in Florida (15:36:14) :
You said:
‘“On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location”
I believe the color coding is for temperature of the cloud tops, the “hot” reds really being colder cloud tops. The temps are used to determine the height of the cloud tops, higher being colder.’
Not true. The color coding is given on the left hand side of the first image in the post and it relates to intensity of precipitation – higher dBz=more intense precipitation.
From “killer Co2 domes” to “murderous UHI thunder & lightning effects.” Whatever next? The science is settled I tells ya.
Seriously, the warmists will not pay any attention to this as it’s not caused by manmade Co2.
Denny (16:39:18) :
I’ll second that. In line with the article, the differences are far more noticeable at night. One thing that always gets me is how cold and warm pockets can be in depressions in the country. Being on the Plains, there are tons of them. It can drop 5-10 degrees in a very short span, then revert when you leave the low spot.
Doesn’t the long post by Paul (15:28:19) : belong in a different thread? If he agrees it was mis-posted, I suggest that it be deleted.
If 80% of the population is in the cities them so would the factories and employment. This would mean more electrical consumtion being drawn to the cities as well.
Hmmmm.
Ref – Hu Duck Xing (16:47:11) :
“Eighty percent of the U.S. population now lives in cities. ”
I don’t know why,,, but I’ve never read that statistic before. I’m sitting here stunned! Must go look for my jaw! I think I may have kicked it under my desk somewhere. I feel foolish that I didn’t know this,,,,,,,,,,,,,,,
_________________________
Believe nothing you read and only half of what you see. It really only looks that way at night from 45,000 feet. During the day it’s actually closer to 70%. But there too, you must realize that “cities” start at populations of 5,000 and go up from there:-) Americans just luv city-life. (Have no idea why.)
Ref – Jimbo (17:24:09) :
“From “killer Co2 domes” to “murderous UHI thunder & lightning effects.” Whatever next? The science is settled I tells ya.
“Seriously, the warmists will not pay any attention to this as it’s not caused by manmade Co2.”
___________________________
I hope you’re correct but I fear you’re not. Give Fat Albert and his gang half a fact and they’ll be out demanding another $450,391,759,975.98 Trillion to move all the city areas West of their current center line in order to avoid these “Mann-made” destructive effects of AGW. Shusssssssssh
São Paulo Brazil is another city where you can see this effect. Before extensive urbanisation, the area was famous for “Manchester England” like drizzle. But now every afternoon during the summer enormous black clouds build up producing huge thunderstorms with torrential rain and flooding.
Billy Liar (17:22:06) : “Not true. The color coding is given on the left hand side of the first image in the post and it relates to intensity of precipitation – higher dBz=more intense precipitation.”
Of course you are correct. I should have been more specific as I was referring to the weather radar most of us get via our local forecasters, Accuweather and Intellicast.
” Billy Liar (17:22:06) :
@Tom in Florida (15:36:14) :
You said:
‘“On weather radar displays, highly reflective areas are thunderstorms, which are typically color-coded in hot colors (i.e., reds, oranges) to make it easy to identify their size and location”
I believe the color coding is for temperature of the cloud tops, the “hot” reds really being colder cloud tops. The temps are used to determine the height of the cloud tops, higher being colder.’
Not true. The color coding is given on the left hand side of the first image in the post and it relates to intensity of precipitation – higher dBz=more intense precipitation.”
Still not right, quite. The colours signify the strength of the reflection of the radar off the density of water in the atmosphere – it need not signify precipitation, necessarily. The picture is of a classical thunderstorm, with leading edge notch (NE is front and the anvil end), and the direction of travel is SW to NE. At the back it has the telltale notch (SW, bottom side) of a weak echo region where the main updraft is going up. Looks like it might have another inflow jet on the other side, opposite. Look like there’s slight rotation to the updraft due to the high echo pattern near the inflows. Heaviest rain will be just SW of the highway “shield” near the center. The purple in the centre suggests there’s light to moderate hail up in the storm. Storm has well defined front and rear downdrafts, so there’s probably lots of wind coming out of it.
The colours are not temperature based as they would be in an infared scan, but density based.
The colours, btw, are entirely arbitrary. The NWS uses a defined set, but there are many variations in common use, and the colour table can be customised to enhance specific features. All the radar spits out is numbers.
Take a look at the orientation of the majority of the runways at DFW; N-S.
Ft. Worth is *west* of DFW and runways are laid out taking _prevailing_ winds into consideration …
.
.
Satellite, you’ re probably thinking satellite imagery, not the terrestrially-based NEXRAD WSR-88D RADAR which observes ‘things’ that an RF (radio) wave can reflect off of; this includes rain, drizzle, snow, birds, space-shuttle debris …
.
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An acquaintence of mine related that she had grown up in Montana. In her youth, dryland farming was the predominant land use pattern. As time passed, more irrigation was installed, so that eventually, almost all of the dry land farms were now irrigated.
Afternoon thunderstorms, never present before irrigation, became a daily feature.
The phenomenon might be related more closely to water vapor than UHI effects.
What about tornadoes? I live just a few miles NE of Dayton, Ohio and many times in the summer big storms will form 10-15 miles east of Dayton(they don’t rain on me but I can watch them build if I look east southeast. Greene county, which is 10 miles east of Dayton, has more tornado reports than other counties around Dayton. The county seat of Greene county is Xenia, which had an F5 tornado in 1974 and an F4 about 10 years ago. Some people have looked at topography as a contributor, but I have never heard any suggest UHI from Dayton as a contributor. However, it would be consistent with this article about Atlanta.
Jimbo (17:24:09) :
Seriously, the warmists will not pay any attention to this as it’s not caused by manmade Co2.
—————————–
Yeah, well that’s why they just invented CO2 domes over cities, that takes care of the UHI and therefore the AGW is actually causing the thunder and lightning. Boo Hoo /sarc off/
Up here in the Great White North, in the summertime, we are experience a phenomena they refer to as daytime heating, which causes thunderstorms to build in the late afternoon for a hour or two. The Calgary area is very dry (low humidity) and it doesn’t matter if the daytime temperature only reaches 60°F it’s still daytime heating. It happens on sunny days and somehow draws the moisture out of the ground to create thunder storms.
People living in Moscow are used to strange winter lightnings over the city, which never appear in the surrounding rural areas. These “winter thunderstorms” started in 1980s, I think, and continue to this day.
Moscow is drastically more built-up and densely populated than almost any other region in Russia. It certainly has it’s own micro-climate these days. Having a half-mad, half-drunk mayor who uses cloud seeding, artillery, and aviation in his (futile) attempts to control weather makes life in Moscow even more interesting. Not to mention the most nightmarish traffic on Earth; I’ve driven in New York, Montreal, London, and Athens — Moscow is worse!
Isn’t this actually good news?
I mean, for real environmental/civil engineers/scientists.
Cities,at least coastal cities similar to Atlanta, cause rain? That’s great! Georgia is out of water, so Atlanta making rain is a good thing.
With more studies, civil engineers can determine where best to put various types of drainage, collection and reservoir type systems.
Environmental engineers,the sane ones, could determine basically the same thing. Perhaps including wetland/forest/’green zone’ development, preservation and things of that nature.
With the extreme weather concerns, this is also good news. It can show the weather folks where to look and what to look for, giving higher quality advanced warning.
This study ties in to the thermostat hypothesis http://wattsupwiththat.com/2009/06/14/the-thermostat-hypothesis/. One question – have any quantitative studies been done on the energy conversion of thunderstorms? If so, it should be possible to do an energy budget for urban heat islands and estimate the feedback effect.
As a resident of Panama, we live smack in the middle of the tropical convergence zone. Although weather records are scarce (no government weather service to speak of), locals tell us that there is much more precip now than in the past, including as this year, in the “dry” season. 2008 brought 310 inches to our mountain community located right at the continental divide.
I live in the I95 corridor in Virginia, just a couple miles west of the Richmond city limits. When I’m watching radars often I see storms coming from the West. Downsloping often makes them fade from view just to the west of the corridor a bit south of me, a few frames later just to the east of the actual line for I95 they pop up again.
Really weird because it looks like the storms went underground then popped up through a hole by the side of the highway. I blame the trucks. 😉
That is an interesting image of a thunderstorm. As an airline pilot flying in the tropical Asia, I see many many thunderstorms and our weather radars typically paint a completely different image to the one presented above. Especially when the precipitation is heavy our radars often suffer severe attenuation. It would be interesting to know how that image was actually formed.
However, I have noticed how convective activity does tend to be present around the cities. Not so good for the airplanes wanting to arrive and depart said cities! But it has to be remembered that TS requires an unstable atmosphere, generally meaning that they will form, it is just a matter of where the first suitable trigger is that the unstable air comes across first. High ground, city or simply relatively hotter terrain compared to the sea.
I can’t imagine that UHI will cause more TS, but may affect where TS will form depending primarily on the 2000′ wind direction. Outside of the tropics, I would imagine frontal weather would be the most common trigger. UHI would be way down the list.
I live in Atlanta. Each thunderstorm season (as we call spring and summer around here), I watch Wunderground’s NexRad products with the glee of a child waiting for the next thunderstorm to roll in. I’m somewhat of an amateur severe storm buff you could say.
I’ve also noticed on many occasions that lines of storms will break around the city perimeter as well as intensify. Many times I’ve watched severe lines that tracked for hundreds of miles simply fall apart around the city and then re-intensify when they’ve gone by.
So yes, the heat island is there, although I don’t think we can say that it will intensify each storm that rolls through. I’d wager to guess that it’s probably about half.
[snip]
No chemtrails posts, please. ~dbs, mod.