Matt Igel

Convective Atmosphere Group

Go Aggies

UC Davis has another team of stellar forecasters attacking the WxChallenge (https://www.wxchallenge.com/) again this year.  Go Aggies.

See the source image

Enjoy a DoNUT at the Equator

I’m very proud of this one.  Check out our newest paper published in EOR in JAS below.  The paper introduces two concepts.  The first is whether or not convective clouds and circulations care about the Cosine terms of the Coriolis Force that we almost always forget about.  The short answer is that they do.  The Cosine terms systematically tilt convection toward the west.  The implications of this are many (future papers), but in the simplest possible sense, clouds care because they are no longer symmetric at the equator.  When viewed from space, Equatorial clouds are not round!  The second is that this paper introduces our new (genuinely inter-disciplinary) conceptual model of convection: the Dynamics of Non-rotating Updraft Torii or “DoNUT” model (the name actually gives away that our development is incomplete so far).  Rather than imagining convection as a plume, we envision convection as a 3D torus.  Doing so allows us to draw some pretty fundamental insights into convection.  We can connect rising and sinking air associated with convective clouds directly.  And, you’ll see in the paper that connection matters.  Here too, more papers to come.

I mention in the acknowledgements that my consideration of the Cosine Coriolis terms was inspired by several ATM 121A (atmospheric dynamics) classes I have taught recently.  This paper would not exist if I hadn’t had some great students in my classes over the years.  We also acknowledge a colleague whose recent passing inspired us to keep pushing (cooking?) the DoNUT.

https://journals.ametsoc.org/jas/article/doi/10.1175/JAS-D-20-0024.1/354631/The-Non-Traditional-Coriolis-Terms-and-Tropical

Bert Dreams of becoming a Meteorologist

Being on parental leave has given me the opportunity to catch up with Sesame Street after 30 years.  In a recent episode, I learned that Bert has always dreamed of being a TV weatherman.  Well, I’m here to be the first to officially invite Bert, and any prospective students who have always dreamed of forecasting the weather for a living, to apply to the UC Davis atmospheric science major.  With a little hard work in our atmospheric science classes, Bert, I know you can get over your stage fright and forecast the weather with confidence!

Family Leave

July 6th marks the first day of my family leave over the summer.  I will be checking email and Twitter but much less frequently than usual.   If you’re awaiting a slow reply to contact, entertain yourself with the newest UCD Cloud Library additions.

Precipitation Free February (2020)

Davis has not seen any precipitation this month and will not see any tomorrow.  The rumor is that this will be our first ever rain-free February.  I looked back through the 50 years of data I’ve used for a couple of these recent posts, and sure enough, in those 50 years, every previous February has seen precipitation.  The remarkable thing about our rain-free February in 2020 is just how much of an outlier this is.  Not only have all previous Februarys seen rain, but the previous minimum number of rainy days in February is 7!

Warning: This is terrible use of statistics!  The climatological probability of precipitation for February days in 36% (i.e. it rains about 1 in every 3 days normally).  Given the 36% likelihood of precipitation on any given day, the likelihood of a rain-free February is just 1 in 229,688 (i.e. (1-.36)28).  If that February has 29 days (like 2020), the likelihood drops to 1 in 356,951.  So, it’s significantly less likely a leap year would have a rain-free February, not just a little less likely as may be intuitive.  Of course, to do this calculation well, I really need a lot more data and some way of accounting for the autocorrelation of precipitation…

As a fun check of the data I do have: Februarys with 28 days have an average monthly rainfall of 3.50” and Februarys with 29days have an average monthly rainfall of 3.67”, or almost exactly 1/28 more.  Cool.

Photo Winner

I thought it was time to add a little intrigue.  Below is my favorite picture from the the ever-growing stack of cloud photos (see right…).  We’ll call it the unofficial 2019 photo contest winner.  This one is of a rain shaft falling from a thunderstorm over New Jersey taken by Lea Tong.  What I think is especially interesting is all the subtle structure in the rain shaft.  What? Don’t see much structure that you think warrants any explanation?  Ah, just wait for my next “forgotten cloud physics” paper to come out some time in 2020!  It’ll “blow” your mind.

NJ Downpour © Lea Tong

Our Simple Precipitation Model

A few days ago, a colleague from UCD Mathematics, Joseph Biello (of MJO fame), and I published a paper in npj Climate and Atmospheric Science.  It’s available here.  We attempted to use well understood aspects of the statistical properties of precipitation to derive a simple model for global precipitation.  Then we populated model parameters with data from satellites and from cloud simulations.  The nice thing is that our model is analytic, and because its constructed from physically understood pieces, it’s very easy to use as a sandbox.  In the paper, we ask what possible future states of precipitation may look like given some arbitrary surface warming.  The cool (or not so cool depending on your perspective) result is that many possible future hydrologies are possible.  Yet models seems to predict a limited range of possible responses in the properties of precipitation.  This could mean two things.  1) There are some consistencies among models that are physically based that we have not identified or 2) the suite of models is not large enough to span the possible responses.  My gut feeling is that its probably a little of both.  What I think is neat about this paper is that we have created an analytic, data-driven model of the climatology of precipitation properties.  We’re hardly the first to do such a thing, but this one is mine.

Cloud Photos

I just wanted to point out all the new cloud photos on this website (look right).  Special thanks to ASGG students Katherine Chin, Jenae Clay, and Megan Schmiedeler for contributing some excellent photos from all over the world.  And more thanks to John (dad) and Jen (sister) for their contributions.  If you’d like to contribute your own photos to the gallery, send me an email.  My plan is to continue to grow this gallery with photos of interesting and unique cloud formations.  My next mission is to reach 100 photos.  Please use these photos with proper acknowledgement to the copyright owner if one is listed. 

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