Tuesday, April 22, 2014

Why are there double rainbows?

There seems to have been an unusual number of spectacular double rainbows around the Northwest during the past week, and several have you sent me some stunning pictures.  Let me show you a few samples.

 Picture Courtesy of Tom Kreyche from Capitol Hill, Seattle

Pictures courtesy of Seelye Martin in Laurelhurst, Seattle

Why TWO rainbows?  Most of the time only one is clearly apparent.

As many of you know, rainbows result when light from the sun enters a raindrop and experiences a reflection at the back of the drop and heads back to the observer (see schematics).  Sunlight has all wavelengths of visible light, from short wavelengths (purple and blue) to longer wavelengths (red and orange), with yellow and green in between.  As sunlight reaches the raindrop it is refracted (bent) upon entering the drop, reflected off the back of the drop, and then refracted again when leaving.  The interesting thing is that the amount of bending during refraction depends on wavelength, with longer wavelengths (e.g., red) bent less than shorter wavelengths (e.g., blue).  This is called dispersion, which results in the sunlight being broken up into a spectrum of colors:  the rainbow.




But sometimes, there are TWO reflections in the back of the raindrop, which produces another rainbow, with the colors reversed (see figure below).  This is the secondary bow, which is generally fainter than the primary bow.  Look at the pictures  above; can you see the reversal of colors?  Red is at the top of the primary bow, but at the bottom of the secondary bow.


Quiz time....is this picture of a double rainbow below real or fake?  The answer: FAKE.  No color reversal between the bows. Someone got carried away with Photoshop.


Spring is rainbow season here in the Northwest.  Why?  Lots of instability, so there are plenty of cumulus clouds and their transient showers. The showers are followed by sun, which helps produce the rainbows. Classic spring showers and sunbreaks!  A winter storm with a continuous cloud deck without breaks is no good for rainbows.

Why is it very unstable this time of the year?  Because  instability is associated with a big change in temperature with height and spring has this in spades.  The sun is strong and warms the surface, while the atmosphere aloft has not warmed appreciably yet.

There is one question about double rainbows I can't answer:  Are there two pots at both sides?  I will leave this important question to others more qualified to deal with it.


Come to think of it, maybe I can answer the question.  This is my kind of gold.  And they make it in Ellensburg!


Sunday, April 20, 2014

Is Asian Pollution Intensifying Pacific Storms? Separating the Hype from Reality.

The media over the past week have given a lot of play to a paper in the journal Proceedings of the National Academy of Sciences (PNAS)  that claims that Asian pollution is enhancing storms over the Pacific Ocean, with effects extending globally.

We are talking headlines in hundreds of major media sources around the world.  As illustrated below, the headlines have been pretty scary.  But as I will show below, the PNAS paper really proves no such thing and this situation is another example of unhealthy and counterproductive hype and exaggeration in the media.






The paper, Assessing the Effects of Anthropogenic Aerosols on Pacific Storm Track Using a Multitscale Global Climate Model (found here) is by Yuan Wang of Texas A&M and collaborators, with the last author being Mario Molina, a member of the National Academy of Sciences (keep this in mind, it will be important later).

The paper claims particles ejected into the atmosphere over Asia (aerosols) are causing "intensification of the Pacific storm track" and "invigorated midlatitude cyclones."   In a press release by Texas A&M, co-author Renyi Zhang states:

“There appears to be little doubt that these particles from Asia affect storms sweeping across the Pacific and subsequently the weather patterns in North America and the rest of the world,” Zhang says of the findings.
“The climate model is quite clear on this point. The  aerosols formed by human activities from fast-growing Asian economies do impact storm formation and global air circulation downstream.  They tend to make storms deeper and stronger and more intense, and these storms also have more precipitation in them. "
And Tech Times states:
Yuan Wang believes the polar vortex that brought frigid temperatures to much of the eastern United States may have been the result of Pacific storms driven by air particles released over China and other nations .    

In a press release Wang stated:

"This cold winter in the U.S. probably had something to do with stronger cyclones over the Pacific,"
So Asians keeping themselves warm is causing cold waves over the eastern U.S. according to an author of this paper.  As we shall see below, such claims are entirely unwarranted.


A little analysis quickly reveals that there is far less  than meets the eye to this paper.  And that there is very little proof that Asian pollution is doing anything to Pacific storms.
Let me begin by noting that the Wang et al. study is limited to modeling.  There is no observational analysis showing that observed storms are intensifying.  No observations showing direct effects of Asian pollution on storms.

This study is limited to looking at two global model simulations:  one assuming the aerosol (particle) conditions of 1850 (preindustrial, PI) and the other the pollution characteristics of 2000 (present day, PD).  So they did not show using observations that storms are getting stronger or that there was a connection with increased aerosols.

What they did do was to run a global climate model twice with an without modern aerosols in the atmosphere.   This study really doesn't isolate Asian aerosols changes as suggested by the text and the resolution is so coarse (around 200- 250 km between the grid points) that they really can't simulate Pacific storms properly in any case.    Their innovation is to run a different approach for simulating convection (e.g., thunderstorms), using explicit simulations, with cloud and aerosol physics modules, rather than what is called parameterized physics (where processes are inferred from larger scale variables).  They never show that their approach does a better job in duplicating observed clouds and storms than more traditional approaches.

Now the fun part.   They describe the results of huge changes in aerosols (again between 1850 and 2000).  But they never show how the winds are changing in the storms.  Or how the central pressures are changing.  Rather they show very indirect parameters.  Kind of strange that they took this approach.   

They show that precipitation over the NW Pacific increases by 2.4%!   And that high clouds increase by 2.6% .   So a huge change in particles over Asia only increases precipitation and clouds by around 2.5% and ON THIS BASIS they are suggesting noticeable strengthening of Pacific storms.  I could make a snide remark on how ridiculous this is, but I won't.   And they found that north-south heat transport over the NW Pacific increased by 5% for this 150-year aerosol change.  Not much.  And for most of their domain (basically China to the dateline) the differences between 1850 and 2000 were NOT STATISTICALLY SIGNIFICANT.


What they should have noted was how AMAZINGLY INSENSITIVE the Pacific storm track is to increased particles in the atmosphere.  

Next, they compare their simulations to a similar experiment using a more traditional (CAM5) climate model. Never do they show that their model is better by the way.  Complexity does not necessarily produce better results.   Anyway, the CAM5 model gives the opposite results, with the storm precipitation and high clouds decreasing.   Quite honestly, this makes just as much sense as their results with more a complex model.   With reflective aerosols pushing out from China and India around 30-40N, that might cause cooling in the latitudinal band, weakening the north-south temperatures gradient, and thus attenuating storms (midlatitude storms depend on north-south gradient for their energy).

And there is something really strange about this study.  They ran the model globally but never show the influence over the eastern Pacific and North America.   Why not?  Why make all kinds of inferences and suggestions about the downstream effects, but don't show the directly relevant information that you have.  

The question you all should be asking at this point is:  how in the world did this paper get published in a supposedly peer reviewed journal?  If I had been a reviewer, I would have immediately rejected it for the reasons noted above and many more.

And there is a dirty little secret here: papers published in PNAS are often...how do I say itpolitely?... "lightly reviewed" , particularly when a member of the National Academy is an author.   Until recently, a member of the Academy could simply wave any paper through.  After some complaints about poor manuscripts they developed an alternative means where the Academy member can serve as editor and evaluate the reviews him/herself.  You notice a member of the Academy was involved with the paper and it is clear that the paper did not undergo the "standard", more rigorous, review process.  And only two reviewers, which is less than usual for most major papers.


What I find particularly disturbing is that  this paper is just one in a series of similarly speculative, generally weak, manuscripts that hype some environmental threat from global warming or some other environmental threat. The media, does not seriously review the work, and goes bonkers over it, with the latest threat becoming headline material all over the world.   There are so many examples of this. For example:


  • That Global Warming is causing the jet to "wobble" producing more cold waves in the eastern U.S.
  • This week this was another paper of this ilk claiming that Global Warming is causing a "dipole pattern" over North America with ridging in the west (think drought) and troughing in the east (think polar vortex).  Future blog material!


Global warming is a serious issue for mankind and rational discussion of its impacts is being impeded by the huge media hype for weak,speculative papers, most of which will be proven to be in error.  And advocacy groups concerned with global warming are not helping their cause by incessantly crying wolf.  The world will eventually stop listening.  Many folks already have.


Friday, April 18, 2014

Crater Lake Contrail Fest

The high resolution image around noon Tuesday from the NASA MODIS Terra satellite was quite interesting (see below).  There was a general veil of high cirrus clouds over the region and some large cloud bands extended downstream from major volcanic peak (see my previous blog for an explanation about those lines).  You could also lo- level clouds west of the Cascade crest over western Washington and NW Oregon.


If you look closely you see some fine lines over the southern part of the domain...those are aircraft contrails. In fact, there were HUGE numbers of contrails.  Here is a close up view of the contrails around Crater Lake in the southern Oregon Cascades.  There were not only a lot of flights, but the contrails were not dissipating very fast.  Why?  Because the air was already at 100% relative humidity...that is why there was so much thin cloudiness around.  The moisture from the planes...the contrails...just enhanced the thin clouds already there and since the atmosphere was saturated already, there was little evaporation of the contrails.


With the contrails thickening the clouds over a large area, there can be major large-scale radiative impacts.  The thickened clouds can reflect more of the solar radiation to space and can also have big effects on infrared radiation heading to space and back to earth.    So if you want to understand climate change, contrails are a small, but significant issue that needs to be considered.

Do contrails cool or warm?  The best estimates now are that they warm the planet due to their impacts on infrared energy (they radiate infrared energy back to earth) outweighing the cooling impacts of reflecting some solar radiation back to space.  That contrasts with the other lines produced by humans seen on satellite imagery:  ship tracks (see image below).  Such lines, produced by the enhancement of the number of cloud droplets in low-level stratocumulus and stratus clouds by combustion products in commercial ships, clearly cool the planet.  In such clouds, the infrared effects are far weaker, so that the reflectance of solar radiation dominates.

Finally, last night a very strong Puget Sound Convergence Zone formed as a Pacific front moved through the region (see radar image below at 10 PM, yellow is heavy rain)


 The 24h precipitation ending 7 AM from Seattle RainWatch (which combines radar imformation with rain gauages) shows the impact of the convergence zone, with some areas getting more than 4 inches!
And some rain gauges (over the same 24 h period) observed three inches and more (see below).   There was a strong rain shadow to the NE of the Olympics yesterday, with some locations getting only a few hundredths of an inch).   Just amazing isn't it?  A hundred times more rainfall roughly 50 miles away.  And far wetter in Seattle's eastern suburbs than along its Puget Sound shoreline.






Wednesday, April 16, 2014

Strange Lines: What are They?

On Monday, something seemingly very strange was found in the visible satellite imagery over Washington. Curious lines extending from major volcanic peaks.  Let me show you.

First, at 8 AM (1500 UTC) there were no lines over the Cascades, but a band of high clouds was moving over western Washington.  You can see snow over the Cascades and the volcanic peaks (like Rainier) are evident as isolated areas of snow.


But then something strange happened.  As the high clouds moved over the Cascades (10 AM), a strange line formed, extending to the east-northeast of Mt. Rainier, with weaker lines associated with Mt. Baker and Mt. Adams.

By 11:45 AM (1845 UTC), the Rainier and Mt. Adam's lines were half way across eastern Washington.


 But then something strange happened.   As the high clouds moved eastward the strange lines disappeared!


Want a better view? Here is an image from the high-resolution MODIS Terra satellite around noon.


And here is a MODIS close up of the lines extending from Rainier and Adams.


So what is it?  Alien spaceship tracks.   Government topic secret program?  Chemtrails?

Nope...there is another answer.

 The winds aloft yesterday were generally from  the west at roughly  10,000 ft (700 hPa ) and west-southwest higher (see radiosonde sounding at 5 PM yesterday).  In the upper troposphere (from 15,000 ft to 30,000 ft) the air was near saturation in this sounding (the temperature--red--and dew point --blue--were close together).


A band of high clouds moved over the region during mid-day.   These thin high clouds indicated that the atmosphere had reached saturation at some upper levels, producing extensive ice clouds.   But something supercharged the high clouds, making them far whiter downstream of the mountains.

The probable cause?  Vertically propagating mountain waves!   Some mountain waves stay low and produce mountain wave clouds over and immediately downstream of mountains near crest level.   But when the conditions are right, the mountains produce waves that move (or propagate) upwards, with their maximum upward velocity well above and somewhat downstream of the mountain (see figure).  In such a wave, the cloud can start downstream of the mountain peak and extend downstream a considerable way.


So we started with a thin veil of clouds...a layer of ice crystals.   Then extra upward motion produces enhanced cooling and production of even more ice crystals. The cloud became whiter.  These ice crystals were not evaporating downstream since the air was generally saturated.   So a long line formed downstream of the mountain.

Later, when drier air moved in, the lift of the mountain waves were not enough to produce ice crystals and the air cleared.   

Could we model this using computer simulation?   You bet.  Here is the UW WRF cloud fields at noon on Monday.  Look carefully and you can see enhanced lines embedded in a general mass of upper clouds.  We have come a long way!


Monday, April 14, 2014

Lunar Eclipse Weather

A total lunar eclipse will begin tomorrow (Monday) night.  The moon moves into the earth's shadow (see schematic) at 10:58 PM, with the total eclipse occurring between 12:07 and 1:25 AM PDT early Tuesday morning.

As we will discuss later, there will be considerable cloudiness during the period, but I suspect several of you will be to view parts of the eclipse.

An interesting aspect of total lunar eclipses is that the moon is never completely blacked out, even though shadowed by the earth (see picture from an earlier eclipse below).  Frequently, the moon takes on an orange or reddish color during totality.


But why does the moon not go completely dark?   The reason:  the earth's atmosphere!

Some of the sun's light is refracted or bent by the earth's atmosphere towards the darkened moon (see figure).
But why is the moon often reddish during a total lunar eclipse?  The atmosphere tends to preferentially scatter and remove the shorter wavelengths of light, like blue and green, leaving longer wavelengths like red.  That is why sunsets are red.


Some eclipses are redder than others.  If the there is a substantial volcanic eruption that injects large amounts of particles into the atmosphere, more of the shorter wavelengths are removed resulting in a darker, redder moon during the eclipse.
So will you see it?  Let's take a look at the latest WRF model forecast for 12 AM Tuesday morning. This figure shows the predicted cloudiness, which unfortunately is considerable, with the suggestion of a convergence zone over central Puget Sound.  But there are some gaps over the northern coast of western Washington and some thin clouds over eastern Washington.  Open around Vancouver and in portions of the Willamette Valley.
 Looking at the 9 AM visible satellite image, one can see that the weak front approaching the Northwest is not very impressive...and quite broken up.  This bodes well for some of you seeing at least portions of the eclipse.  So don't give up!
Now if you miss this eclipse because of clouds, don't worry, this is the first total lunar eclipse in a series of four, also known as a "tetrad", with follow-on eclipses on October 8, 2014, April 4, 2015, and Sept 28, 2015.
Announcement

There’s an interested lecture series starting this week:  Our Global Ocean: The Ultimate Planetary Life Support System--New Approaches to an Old Ocean. A much better title would be 20,000 Gigabytes Under the Sea. The speaker, UW professor of oceanography John Delaney, is leading the team of scientists and engineers at the UW who are building the world’s largest underwater cabled observatory off the coast of Oregon to better understand the complex ocean system that modulates climate.  Lectures will be at 7 pm in Kane Hall on April 15 and 29, May 6 and 20. This event is co-presented by the UW Alumni Association and by Seattle Arts and Lectures. Register and buy tickets through the SAL website here