The rain in Spain is mostly from the planes

A radar tower at London Heathrow Airport

Heathrow airport. Image via Wikipedia

OK, bad pun, but I could not resist.

From the National Center for Atmospheric Research/University Corporation for Atmospheric Research  something related to what we have always said, airports are not a representative environment for climate measurement.

Takeoffs and landings cause more precipitation near airports

BOULDER–Researchers have found that areas near commercial airports sometimes experience a small but measurable increase in rain and snow when aircraft take off and land under certain atmospheric conditions.

The new study led by the National Center for Atmospheric Research (NCAR), is part of ongoing research that focuses on so-called hole punch and canal clouds that form when planes fly through certain mid-level clouds, forcing nearby air to rapidly expand and cool. This causes water droplets to freeze to ice and then turn to snow as they fall toward the ground, leaving behind odd-shaped gaps in the clouds.

The research team used satellite images and weather forecasting computer models to examine how often this type of inadvertent cloud seeding may occur within 62 miles (100 kilometers) of six commercial airports: London Heathrow, Frankfurt, Charles De Gaulle (Paris), Seattle-Tacoma, O’Hare (Chicago), and Yellowknife (Northwest Territories, Canada), as well as Byrd Station in Antarctica. They found that, depending on the airport and type of plane, the right atmospheric conditions typically exist up to 6 percent of the time, with somewhat more frequency in colder climates.

The lead author, NCAR scientist Andrew Heymsfield, says this phenomenon likely occurs at numerous other airports, especially in mid- and high-latitude areas during colder months. The key variable is whether there are cloud layers in the vicinity that contain water droplets at temperatures far below freezing, which is a common occurrence.

He adds that more research is needed before scientists can determine whether the precipitation produced by this effect is significant. The inadvertent cloud seeding may increase the need to de-ice planes more often, he adds.

“It appears to be a rather widespread effect for aircraft to inadvertently cause some measureable amount of rain or snow as they fly through certain clouds,” Heymsfield says. “This is not necessarily enough precipitation to affect global climate, but it is noticeable around major airports in the midlatitudes.”

The researchers did not estimate the total amount of rain or snow that would result from such inadvertent cloud seeding. However, they analyzed radar readings that, in one case, indicated a snowfall rate of close to an inch an hour after several planes had passed through.

The study is being published this week in the journal Science. Researchers from NASA Langley Research Center and the University of Wyoming, Laramie, co-authored the paper. Funding came from the National Science Foundation, which is NCAR’s sponsor, and from NASA.

Solving a cloud mystery

Scientists for decades have speculated about the origins of mysterious holes and canals in clouds. Heymsfield led a study last year establishing that the gaps, which sometimes look as though a giant hole punch was applied to a cloud, are caused when aircraft fly through midlevel clouds that contain supercooled droplets.

When a turboprop plane flies through such a cloud layer with temperatures about 5 degrees Fahrenheit or lower (about -15 degrees Celsius or lower), the tips of its propellers can cause the air to rapidly expand. As the air expands, it cools and causes the supercooled droplets to freeze into ice particles that evaporate the droplets and grow, falling out of the clouds as snow or rain.

Jet aircraft need colder temperatures (below about -4 to -13 degrees F, or -20 to -25 degrees C) to generate the seeding effect. Air forced to expand over the wings as the aircraft moves forward cools and freezes the cloud droplets.

The effect is unrelated to the trails of condensed water vapor known as contrails made by the exhaust of jet engines.

In the new research, the study team used cloud measurements taken by the NASA CALIPSO satellite to quantify how often such conditions exist within about 62 miles of several airports located in relatively cloudy areas. They chose the 62-mile radius because that is approximately the distance it takes for a commercial aircraft to climb above about 10,000 feet, where many of the supercooled cloud layers are located.

Of the major, mid-latitude airports studied, they found that the Frankfurt, DeGaulle, and O’Hare airports most frequently experienced the right conditions for propeller aircraft to generate precipitation. In each case, the conditions existed more than 5 percent of the time over the course of a year. The researchers found that the right conditions existed more than 3 percent of the time for jets at Heathrow, Frankfurt, and Seattle-Tacoma.

Yellowknife experienced such conditions more often, about 10 percent of the time for propeller planes and 5 percent for jets, presumably because of colder cloud conditions at higher latitudes. Byrd often experienced the very cold conditions that enable jets to cause inadvertent cloud seeding.

The researchers also found that a diverse range of aircraft can induce precipitation. By comparing observations of hole-punch and canal clouds made by a National Oceanic and Atmospheric Administration (NOAA) satellite with flight path records from the Federal Aviation Administration, they confirmed that commercial jets (such as Boeing 757s and the McDonnell Douglas MD-80 series of jets), military aircraft (B-52s), various regional and private jets, turboprops, and prop/piston planes all can induce precipitation.

Hole-Punch Cloud

Aircraft-induced hole observed at the West Antarctic Ice Sheet Divide Camp, Antarctica (79 28.058 °S 112 05.189 °W, 1806 m elevation) on Dec. 12, 2009, 1400 New Zealand Time. The cloud's bright cumuliform structure with gray fallstreaks below are visible. The hole first appeared on the horizon and then moved toward the camera. It is likely that a LC130 aircraft produced the ice that formed the hole. Photo provided by Eric Zrubek and Michael Carmody. For more information, please see Figure 1A in the manuscript. Credit: Image courtesy of Science/AAAS


“It appears that virtually any airplane that flies through clouds containing liquid water at temperatures much below freezing can cause this effect,” Heymsfield says.

Satellite readings analyzed by the team showed that holes and canals generated by aircraft can occur with some frequency. For example, an extensive cloud layer over Texas on January 29, 2007, contained 92 such gaps, some of which persisted for more than four hours and reached lengths of 60 miles or more.

Heymsfield and his colleagues also used a powerful software tool, known as the Weather and Research Forecasting model, to learn more about how the holes form and develop. They found that the hole rapidly spreads about 30 to 90 minutes after an aircraft passes through. This would be the peak time for precipitation associated with the cloud-seeding effect. After about 90 minutes, ice and snow begin to dissipate.


The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.


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Cure for drought? Just keep flying in and out of drought-stricken areas…
I don’t find this surprising, but I do wonder if there are also conditions where aircraft suppress precipitation, achieving some sort of balance. It seems like we only hear one side (a potentially problematic side) to any discovery like this.
One thing is for sure: no matter what negative impacts aircraft might have to the environment, I know they’ll never stop flying altogether… how else would the environmentalist greeny AGW types get to their lavish parties?

kadaka (KD Knoebel)

Contrails were briefly mentioned. Where is the obligatory “No talk of chemtrails!” warning?

Isn’t that interesting! Just this morning I suggested an alternative to aircraft: wheel barrels!
Read about it here

Wayne Delbeke

But, but … it’s from Boulder. Where is a comparable or confirmatory study?

There is a study in Portugal, by a renown scientist, that says that it rains more during the weekends…

Wayne Delbeke

Not sure this is exactly new, there are references back to the 60’s on the effect of aircraft flying through clouds, and using helicopters to make holes in fog or to clear runways. But I suppose we now have the ability to measure in new ways as well as observe.


I bet that we will have to wait for a similar study on urban heat islands quite a bit longer. But it is a start.
Rgds from Chile


None the less, it is important to know the weather at the airport if you are going to land or take off. It is just inappropriate to use it in your climate data set.

Scott Covert

Was this study aimed at solving the mystery of “Hole-Punch Clouds” or is there a practicle use for the study?


“…It appears that virtually any airplane that flies through clouds containing liquid water at temperatures much below freezing can cause this effect,” Heymsfield says…”
Question, then – could this inadvertant cloud seeding be caused by a turboprop or jet flying through the outerbands of a hurricane?
Are the Hurricane Hunters causing SLIGHT changes in the storm intensities?
Could their PATH through the hurricane cause changes in one quadrant, and possible steering effects?
Or will this need more research?

Ed Barbar

Just another indication that even getting a good understanding of temperature and other weather phenomenon is really hard.
I sometimes think the modelers have a bit of disdain for the measurers. It reminds me of a sentiment in J.R. Brownowski’s “The Assent of Man,” which stated something to the effect that the woodcutter is the scientist, because he exposes what is in the tree, and observes nature, whereas the potter merely discovers the shape of his hand.

Gary Swift

“Cure for drought? Just keep flying in and out of drought-stricken areas”
Yeah, with cargo planes full of water. I think trucks would be better though.


Do you notice how they said “forcing the air to rapidly expand and cool”.
Unless they have found some new laws of thermodynamics the air does so because it has been warmed and then rises (key word, “warmed”). But I guess they didn’t want to say that.

6% of the time you get the effect.
in one case they noted a 1 in/ per hour increase in snow fall. err that’s like 1/10 of an inch of rain
portland gets 37 inches of rain per year ( down town)
you have ~200 days a year when it doesn rain in portland.. so maybe this gives
you 10 more days when you get 1/10 inch per hour… another 1inch per year max
if that rainfall even lasts an hour
Assuming that the precipitation gauge is in the vicinity of the actual rainfall, which happens
AWAY from the airport ( up to 62 miles away )
hmm. I’m thinking that finding any corruption in the data from this effect is going to be tough or impossible.

climate creeper

Oh noes! We need a UN committee to deal with anthropogenic precipitation disruption! It’s worse than we thought!

Pamela Gray

Meh. We often have cloudless rain in and around the high plateaus of NE Oregon. Dust kicks up. Water vapor condenses around the dust, rain falls. But unless the rain gauge is right there, no rain will be recorded. Yet it is just as wet under one of these cloudless rain events.

Billy Liar

Call me a skeptic but I think most of those fall streaks that occur with either hole punch clouds or contrails are virga. They don’t reach the ground.

So basically UHI does not exist but planes cause an almost minuscule amount of increase in precipitation…


The “hole-punch cloud” picture in the post, is just another example of “virga” :
“In meteorology, virga is an observable streak or shaft of precipitation that falls from a cloud but evaporates before reaching the ground. At high altitudes the precipitation falls mainly as ice crystals before melting and finally evaporating; this is usually due to compressional heating, because the air pressure increases closer to the ground. It is very common in the desert and in temperate climates. It is also common in the Southern United States during summer.”….
Unless the air near the ground is near its saturation point anyway, the seeded moisture will never collect in a “rain” gauge.
Interesting as a thought experiment, but IMO the money could have been better spent.

Common Sense

Airports can be inaccurate for another reason too. In Denver, Stapleton International Airport was on the east side of the city. When it was built, it was in the middle of nowhere, but eventually became surrounded by city leaving it no room to grow and battling noise complaints (I say don’t buy a house near an airport).
Along comes Denver International Airport, built on land way to the northeast, out on the plains where the weather is far more capricious, the land of small tornadoes and snow fences.
So what do they do with weather records? Why, they combine them like they were always from the same location. There should be an asterisk next to every “record” recorded since the beginning of DIA.

“He adds that more research is needed”
Translation: “Send us more money – LOTS more money – indefinitely”

lowercasefred says:
June 30, 2011 at 1:38 pm

Do you notice how they said “forcing the air to rapidly expand and cool”.
Unless they have found some new laws of thermodynamics the air does so because it has been warmed and then rises (key word, “warmed”). But I guess they didn’t want to say that.

This post is not about convection, it’s about the passage of propellers and wings through a fairly stable cloud deck. The rapid expansion is due to the angle of attack of the airfoil through the air – the top back edge has greatly lowered pressure, and the cooling associated with it forces some supercooled droplets to freeze. Once the airfoil passes by, the air temperature warms back up. And beyond what it was, largely thanks to the heat released from freezing water droplets. The temperature remains below freezing and the ice crystals don’t melt.
Once frozen, the ice crystals attract water molecules from water vapor more strongly than do water droplets, the net effect being that the ice crystal grow and water droplets evaporate. As the ice drifts through the cloud they clear out a volume much greater than what the airplane disturbed.


About the title:
The rain in Spain is *mainly* from the planes

Al Pipkin says:
June 30, 2011 at 12:11 pm
Isn’t that interesting! Just this morning I suggested an alternative to aircraft: wheel barrels!
Read about it here

No sign of that there, just another demonstration of the futility of wind power.
2 Edit notes: “The results were reveling” means partying, celebrating. “Revealing” is what you wanted.
And it’s “wheelbarrows”, not “wheel barrels”.

Duncan says:
June 30, 2011 at 7:47 pm
About the title:
The rain in Spain is *mainly* from the planes

And it generates hydro power, so that the Mains in Spain fill Planely from the Rains.


And planes also create lightening. Twice I have flown though a cloud and triggered the only thunderclap of the day (according to ATC).

Bernd Felsche

I suggest that it has a great deal to do with turbulence and how it is able to concentrate a portion of the energy from the moving object flying through the air into “small” eddies. That energy is enough to form droplets in moist air so it’s not a huge leap to consider that such “parcels” of energy could be enough to cause the suspended cloud droplets to coalesce into precipitable droplets.
Another plausible influence of “flying” objects is electrostatic.
Now; consider what climate effects extensive, off-shore wind farms will have. Notionally, their operational turbulence producing more low-level condensation “downstream”, and having done so; preventing that water vapour from rising to rain-cloud level over ttime.


Kadaka @ 1208:
I thought the ban was on the use of the term ‘chemtrail’… not ‘contrail’.


From the photo caption: “It is likely that a LC130 aircraft produced the ice that formed the hole.”
The entire thesis of this study is a WAG (Wild-Ass-Guess). The idea that the transition of an airplane through part of the atmosphere does anything more than temporary is typical of the crap that passes for research today. This is especially true of academic and government research. I am probably not understating the truth when I say that 98% of academic, NGO, and government research is pure garbage.
The reason I don’t lump in corporate research is because corporations are accountable to their shareholders and money managers, and while it may not be perfect, it is better than what comes out of the other sources.

kadaka (KD Knoebel)

From Ecotretas on June 30, 2011 at 12:26 pm:

There is a study in Portugal, by a renown scientist, that says that it rains more during the weekends…

It was a long-established weather pattern to have increased precipitation in the Northeast US on the weekends due to increased Midwest particulate emissions during the workweek, industrial and from power plants. Here in Pennsylvania it was cited by weathermen for the normal weekend rains which started around Friday during the non-winter months. Stack scrubber requirements seem to have broken it, but there may still be a statistically-significant increase.
What are the wind patterns over in Europe? Can Portugal be receiving particulates from “dirtier” countries like the former Soviet states that have increased workweek emissions?


Looks like what is going on is that agitating supercooled water causes it to freeze.
This is also the basis behind the trick of causing a bottle of water/beer/etc to instantly freeze by tapping it.
The other way in which aircraft could contribute to rainfall is that one of the combustion products is steam. With the highest engine power being Take Off Go Around, which is routinely used at and close to airports.

Wonder why this particular study is hitting all the regular news outlets, when thousands of weather-related studies of equal or greater importance go unreported? Is it simply the fact that it shows a man-made sin? Or does some specific government agency or corporate share price stand to benefit from public awareness of this rather rare phenomenon?