From NASA JPL, video animation follows.
Wet weather is again hitting drought-stricken California as the second and larger of two back-to-back storms makes its way ashore. The storms are part of an atmospheric river, a narrow channel of concentrated moisture in the atmosphere connecting tropical air with colder, drier regions around Earth’s middle latitudes.
The storm that arrived on Feb. 26, 2014, and the one about to hit, are contained within the “Pineapple Express,” an atmospheric river that extends from the Pacific Ocean near Hawaii to the Pacific coast of North America, where it often brings heavy precipitation. This next storm is expect to be the largest rain producer in Southern California in three years.
This animation, created with data acquired by the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua satellite, shows the total amount of water vapor contained in the atmosphere for most of the month of February if it were all to fall as rain. Typically, the atmosphere over Southern California and most of the continental U.S. in winter holds only about 0.4 inch (10 millimeters) or less of water vapor. However, much wetter air lies tantalizingly close in regions to the south and west. The largest amounts of atmospheric moisture, up to 2.4 inches (60 millimeters), are associated with a persistent band of thunderstorms circling the tropics. These thunderstorms are the source of several atmospheric rivers apparent in this animation. One atmospheric river arises near Hawaii around Feb. 10 and comes ashore in Central California a few days later, bringing the largest Sierra Nevada snowfall of the season to date. Other atmospheric rivers can be see originating in the Gulf of Mexico and extending into the Atlantic on the right side of the movie; the northward movement of tropical water vapor is important in winter storms in the eastern U.S. and Europe. The animation concludes with the current Pineapple Express. Moisture from around Hawaii has surged northeast, and the persistent, dry air immediately west of Baja California has been replace by air with up to 1.6 inches (40 millimeters) of water vapor. The next storm will bring that moisture ashore, where it will be forced upward by coastal mountains to fall as heavy rain. Up to 8 inches (20.3 centimeters) of rain is predicted in some parts of the Los Angeles area by March 2, bringing possible flooding and landslides to recent wildfire burn areas.
The recent cold conditions in the eastern U.S. are also apparent in this movie as very dry regions. Because cold air can hold relatively little water (less than 0.4 inch or 10 millimeters), cold region are always dry. So, the eastern U.S. has some of the driest air in this animation. However, high pressure systems also dry the atmosphere by forcing down air from above.
That descending air expands and warms, but retains the low moisture amounts it had when it was higher and cold. So, cold Minnesota and warm Mexico have similar water vapor amounts in this movie.
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Dan in California says:
February 28, 2014 at 3:05 pm
From the article: “The recent cold conditions in the eastern U.S. are also apparent in this movie as very dry regions. Because cold air can hold relatively little water (less than 0.4 inch or 10 millimeters), cold region are always dry.”
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This is sloppy thinking or sloppy writing. Air doesn’t “hold” the water, any more than the nitrogen “holds” the oxygen or CO2. It’s the volume and temperature that “hold” the water.
Dan, you say it’s the volume and temperature that “hold” the water – volume and temperature of what? The cold air, perhaps? So, what you say “holds” the water does not differ from the article in meaning, merely in word choice. Methinks your criticism displays the sloppy thinking.
-“That descending air expands and warms”
I’m sorry to have to ask what may be a rather basic question, but by why mechanism does the descending air expand? I had always been under the impression that the atmosphere was arranged with the denser air closer to the earth’s surface.
Also, it would seem to me that expanding air would cool, wouldn’t it?-
If you *somehow* cause a chunk of air to fall, it will warm.
And because it is warmed, it will expand.
So if you had a huge fan in in sky facing toward the surface, that could the cause of this.
So fan and it’s large extension cord, explains where the energy is coming from.
And for chunk of air to fall it needs some source of energy- something driving it.
So that warmed air has energy, is practically redundant, but for there to be descending air there also has to be energy which is involved which causing this to occur.
If a dry air mass is rising it cools and expands, if dry air is falling it heats and expands- due to it becoming heated
If wet air rises, it cools and water can condenses [warms]. When wet air falls it warms and if water can condense [it warms].
So follow the energy.
Sunlight is the source of energy and the warmed air and evaporated water is the energy which has been converted from energy of sunlight
Or “weather” are engines which are converting energy- which tend to involve water vapor as the fuel for these engines.
Thank you all for your kind replies.
Mario Lento says:
February 28, 2014 at 5:28 pm
How can a parcel of air of a given mass get more dense while also expanding? I had always imaged density to be the ratio of mass to volume.
MaxLD says:
February 28, 2014 at 7:22 pm
“Not with an adiabatic process in the atmosphere, which is a basic process of the atmosphere.”
That would be what I would think.
gbaikie says:
February 28, 2014 at 5:51 pm
“If you *somehow* cause a chunk of air to fall, it will warm. And because it is warmed, it will expand.”
But then, by expanding, won’t it cool back down? Its temperature rises in proportion to the increase in density (someone once intimated to me that PV=nRT — would this apply here, at least approximately, or does R somehow change?).
John F. Hultquist says:
February 28, 2014 at 9:08 pm
“Perhaps the text has the wrong word!”
That could be the case, but I don’t feel I’m in a position, with my rather feeble understanding of the laws of nature, to suggest it in so many words. But, assuming it’s an error, does it then somehow weaken the explanation of the process in the article?
Some interesting warnings, watches, alerts and statements.
http://www.eldoradocountyweather.com/current/misc/google-maps-radar/us-mosiac-radar.html
Sun Spot says:
February 28, 2014 at 12:32 pm
The “Dirty Thirties” encompassed a decade of drought. There was never a reason to think it wouldn’t happen again.
Sun Spot, dontcha know that weather history started in 1979, a year with the coldest temperatures since the Little Ice Age and the highest Arctic sea ice cover since the satellite era began? Sheesh!
Robert Wykoff says:
February 28, 2014 at 12:53 pm
So since the drought is caused by global warming, will the mudslides also be caused by global warming?
I believe Mr. Wykoff should win a prize when the media reports the above!
We are moving from the disaster of a lifetime to mere disaster. I hope it rains until June. That is a lot to ask, though.
The good, the bad, and the ugly. California gets drenched in much needed rain. Oregon gets its wheat crop hammered with the third wave of freezing temperatures.
This page with reservoir data in California is always interesting.
http://cdec.water.ca.gov/cgi-progs/current/RES
Ric Werme says:
February 28, 2014 at 4:42 pm
=========
Thank you for your response.
Please note in the animated graphic as linked in the lead post that it begins on Feb 1 and ended Feb 23. At the end it appears to show the low forming off Cal. So I guess you would be right as to the current supply of moisture. Would it be likely that much of that earlier atmospheric river is now caught up in the low? I wish I could find out how to reach archives with regards to the wind map beginning several days ago.
If you’re talking about the earth.nullschool.net map, click on “earth” and select the double caret [<<] in the "control" line until the URL shows you the day you want. Or you could alter the url.
-“That descending air expands and warms”
Not with an adiabatic process in the atmosphere, which is a basic process of the atmosphere.
This from Wikipedia is a pretty good explanation of adiabatic heating and cooling (with some of the math if you want to go into that).
http://en.wikipedia.org/wiki/Adiabatic_process
The relevant parts for the atmosphere are:
“Adiabatic heating also occurs in the Earth’s atmosphere when an air mass descends… When a parcel of air descends, the pressure on the parcel increases. Due to this increase in pressure, the parcel’s volume decreases and its temperature increases, thus increasing the internal energy.”
“Adiabatic cooling occurs in the Earth’s atmosphere with orographic lifting and lee waves, and this can form pileus or lenticular clouds if the air is cooled below the dew point. When the pressure applied on a parcel of air decreases, the air in the parcel is allowed to expand; as the volume increases, the temperature falls and internal energy decreases.”
Search around for adiabatic process in the atmosphere and I am sure you will find lots of articles.
Joseph Bastardi says:
February 28, 2014 at 1:11 pm
============
Sea surface temps are considerably warmer the further south you go from Alaska. http://www.ospo.noaa.gov/Products/ocean/sst/contour/
Where did the greatest amount of moisture come from that is caught up in the current low? Did that earlier atmospheric river lead to the creation of that low?
Ain’t that impressive? Saw that on the Water Vapor imagery ‘loop’ a few hours ago …
.
Ric Werme says:
February 28, 2014 at 4:42 pm
===============
Ric,
The link you offered in your comment http://www.ospo.noaa.gov/data/sst/anomaly/2014/anomnight.2.27.2014.gif is of sea surface temp anomaly.
You know that is not actual temperature, but temp above/below some average. As noted in the comment to Bastardi above the actual temps can be seen here http://www.ospo.noaa.gov/Products/ocean/sst/contour/
Mixing apples and oranges in the same basket can/does cause confusion.
More fun with the weather can be seen here. http://www.goes.noaa.gov/srchwest.html
Play around with it. Go back a couple of weeks and advance daily. Neat!
It would be nice if someone here could animate over a period of a few weeks.
policycritic says:
February 28, 2014 at 7:19 pm
============
Many thanks.
goldminor
Your comments on links between UK weather and Californian weather are interesting.
I would suggest that you might get quite a bit of rain in 2014 as well as in 2016/7, since in Britain we had a major drought from 2010 to April 2012 (at which point a third dry summer/winter would have led to major Government headaches), which broke decisively in the second quarter of 2012, resulting in a very wet, washout summer.
Summer 2013 was hot and dry after a late winter and cold spring. The heavy rains started in December 2013 and continued for 3 months.
If the links are similar, you might also like to look at autumn/winter 1976/7 in the UK (which was very, very wet following the hottest driest summer in living memory) and whether or not you saw a drought in 1978 and a very wet winter of 1978/9.
1929/30 in the UK also had an incredibly wet winter, so you might want to look at the the 1931/33 period to see in California suffered similarly.
Hyper physics addresses the “warm air holds more moisture” issue.
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html#c5
Kate Forney says:
February 28, 2014 at 1:04 pm
Perhaps the text has the wrong word!
Air pressure is the concept that molecules move and hit each other or a surface. The more of them and the more rapidly they move the more force they exert and that is the pressure. The SI unit for pressure is the pascal (Pa), equal to one newton per square metre.
http://en.wikipedia.org/wiki/Pressure_measurement#Units
Note under the table the 2nd paragraph about “once commonly measured” and so on. A careful reading indicates why the term “weight” has been used in the past, as in “the weight of the atmosphere” but this is considered outdated terminology.
http://en.wikipedia.org/wiki/Thermal_motion#Temperature_and_kinetic_energy
This site has a cartoon-like animation under which it says, “The temperature of an ideal monatomic gas is a measure of the average kinetic energy of its atoms.” Find the heading “Assumptions” — there find easily understood aspects of the ‘ideal’ situation.
High cold air has molecules mostly of nitrogen and oxygen thinly distributed and of low average kinetic energy. Thus, a low temperature. With relatively low buoyancy beneath this air, gravity can pull the molecules toward the surface and by so moving, they get closer together. Think of the number being the same while the volume contracts. So, density increases. Being more densely packed they tend to collide more frequently and the average kinetic energy increase. This is measured as an increasing temperature.
In a large high pressure system over the ocean the descending air can warm to the point that it is a bit warmer than the air in contact with the ocean. This produces a temperature inversion (warm over cool) rather than the expected tendency of near surface air of cool above and warm below – that causes the air to “turn” (the Troposphere).
In the subtropical areas there are large persistent HIGHs such that they have names. Search, for example for Azores High. Because of the situation described in the previous paragraph, the horizontal air (wind) can be extremely calm and the air hazy with water vapor. For those on sailing ships these areas were avoided. For example, Columbus did not attempt to sail across the Atlantic (he knew that would not work). He went south and picked up the winds blowing out of the High and headed to the southwest.
When sailing from England (with napped; as in kidnapped) drunks on board they often reached the edges of the calm just about the time the “dead horse” (aka bar tab paid by the captain where the napping took place) was paid off. A ceremony using a straw horse effigy and the singing of shanties resulted. Search for the “Dead Horse shanty.” Also, here search for horse.
http://en.academic.ru/dic.nsf/enwiki/186612
Getting off topic here so now you are on your own.
I’m looking at a couple of open tabs on my browser at the moment. One is NASA GOES west, an archive page of the same, and the other is the wind map.
http://weather.msfc.nasa.gov/GOES/goeswestpacuswv.html
http://earth.nullschool.net/#current/wind/surface/level/orthographic=-112.07,35.33,455
http://weather.msfc.nasa.gov/GOES/goeswestpacuswv.html
The satellite data is from 8 km elevation.
The wind (surface) map shows a lot of air flow across the warm ocean surface in a region that appears on the satellite to be dry at 8 km elev. It would seem that a considerable amount of moisture is being picked up from west and south of the center of this low and being directed towards southern Cal. that is not showing on the satellite.
In terms of the total water held how would the quantity/volume of water compare between the lower warmer air and that identified by the satellite at 8 km.
Just trying understand Bastardi’s comment above.
That long narrow band/stretch of dry air per the satellite data at 8 km is interesting. Could there be some sort of mega downdraft at/to lower elevations associated with this?
Those archives are so much fun. Will be looking back at them again along with the precipitation reports for Cal. this weekend.
One thing I can agree with Bastardi on is that weather is complex.
“Ric Werme says:
February 28, 2014 at 4:42 pm
Please note in the animated graphic as linked in the lead post that it begins on Feb 1 and ended Feb 23. At the end it appears to show the low forming off Cal. So I guess you would be right as to the current supply of moisture. Would it be likely that much of that earlier atmospheric river is now caught up in the low? I wish I could find out how to reach archives with regards to the wind map beginning several days ago.”
When I was looking at this the other day, we did have a pretty good AR set up which I believe did at least contribute some of the moisture into the present closed low. So while this isn’t a Pineapple Express (AR), an earlier one probably had some contribution. By the way, there’s another beginning to set up farther to the west which has a chance (slight) of bringing a more AR-type of event to the west coast next week.
Here’s a very good resource page for ARs: http://www.esrl.noaa.gov/psd/atmrivers/
Rhys Jaggar says:
February 28, 2014 at 8:32 pm
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Yes, it was partly observations from those years as well as from historical records of the past that made me wonder about the connection. California and further north into Oregon had a drought period from late 1974 through to 1977, before normal rains set back in. 1978 through 1980 were wet years.The late 1920s shows several years of drought until 1932 which was a wet year. 2010 to 2012 was wet. There is an offset in the records. I will take a closer look to see if the pattern can be better understood.
Maybe the “One” did a rain dance on the greens.
crosspatch says:
February 28, 2014 at 11:57 am
……
and here too
http://earth.nullschool.net/#current/wind/isobaric/1000hPa/orthographic=-136,30,672