Matt Igel

Convective Atmosphere Group

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Spring Training

So, it’s every baseball fan’s favorite time of year again.  No, not the World Series, not the All-Star game, but Spring Training.  It’s a special time in the baseball season when guys wearing number 97 run their hardest to catch a meaningless fly ball hit by Albert Pujols in a 10-2 blowout in an earnest effort to make the Major League team…or at the very least, to have their name associated in some small way with a future Hall of Famer.  Well, OK, maybe it’s not every baseball fan’s favorite time of year.  But, it’s definitely one of mine.

Anyway.  I’ve decided recently that Spring Training is a fantastic metaphor for a university course.  For veterans (the professors) who are already on the team, Spring Training (the course) is a chance to relearn the basics — be they executing a double play or doing integration by parts for the first time in a year.  It can be a source of entertainment and a welcome return to a routine in an otherwise chaotic calendar.  For the prospects (the students) wearing number 97, games (tests) and workouts (homeworks) are a great opportunity to learn something new (duh), see how things work at game speed in the Show (“Let’s derive the vorticity equation from first principles”), impress the front office guys (maybe, future employers? ), and catch a lazy fly ball hit by one of the veterans (keeping track of negative signs while deriving things on a white board is hard…).  So, here’s to every baseball fan’s favorite time of year, Spring Semester.

Total Precipitation is Rate Times Duration

I wanted to discuss a recent paper by a fellow member of the UC faculty, J.D. Neelin down at UCLA, and several of his collaborators.  This paper lays out in a very simple way the manner in which total storm rainfall will likely change under global warming conditions.  What I think is particularly useful about what the authors do in their work is that they note not only that storm intensity will likely increase under global warming but also that storm duration might change.  Total rainfall from a storm (or at a particular location on Earth) is the result of the storm intensity and the storm duration.  A colleague of mine back at Colorado State was fond of saying that “the most rain occurs where it rains the heaviest for the longest” which is a very simple statement but one that has often been forgotten in the global warming discussion.  There are many practical reasons for this neglect, not the least of which is that we often lack temporal resolution of storms in climate models, our chief tool for predicting a future world.  Neelin et al point out that the largest storm-total-accumulation values will likely rise due to global warming.  And, I would suggest that their argument for why this is true relies uniquely on physical reasoning.  We observe that many properties of clouds, including, apparently, total storm accumulation, obey simple power-law scalings.  Global warming will likely affect the properties of these power-laws which will likely result in higher frequencies of what would in the current climate be considered extreme rainfall accumulations.  Anyway, check out the paper — it’s freely available at PNAS.

Source: Global warming precipitation accumulation above the current-climate cutoff scale — Neelin — 2017 — PNAS

California Gets High

We often hear about meteorological records being broken.  That is especially true for high temperatures, which is a symptom of global warming, and record rainfalls, which some argue is also symptomatic of global warming but which I would argue is simply the result of the oddity of the statistical distribution of precipitation…but that isn’t the point of this post.  The point is that those of us in the central valley approached another type of all-time record this weekend without much fanfare .  We approached the all-time high (atmospheric) pressure record at the Sacramento Airport this weekend.  On Saturday at 9:53am PST, the sea-level pressure recorded was a whopping 1036.6 mb.  That’s seriously high.  The all-time January record is barely higher at 1037.6 mb.  The difference between yesterday’s pressure and Earth’s standard pressure of 1013 mb is the same as the difference between the standard pressure on Earth and some tropical storms (but in the opposite direction)!

It’s All About Optical Thickness

I was flipping through my (digital) stack of papers and articles to read this afternoon when I stumbled upon a commentary article I’ve had sitting around for a few months.  Tropical anvil clouds and climate sensitivity reviews in an easy to read way the basic state of our knowledge regarding the radiative heating of clouds in the current climate.  The point I found most interesting is one buried toward the end.  The author argues that the new challenge facing cloud-climate types is to determine a general physical law governing the relative distribution of optically thick clouds (which will cool the climate all else being equal) and optically thin clouds (that will warm the climate all else being equal).  This is precisely the kind of work we do here in the Convective Atmosphere Group.  Why are some clouds tall and narrow?  Why are some short and wide?  Increasingly, climate predictions will depend on answering those kinds of fundamental questions.  It’s all about that optical thickness.

Also, I am now an official CocoRaH’s observer: “0.7 miles NNE of Davis”.  You should join too.

More Weather Along the Capitol Corridor

Along with all the rain and the absolutely incredible snow totals in the Sierra, NWS confirmed yesterday the occurrence of an EF0 tornado just south of Sacramento on Jan. 10.  There was very little damage reported, and this was nothing like the tornadoes that occur in much of the country, but it does serve as a reminder that tornadoes can occur across the United States.

 

Another Wet Weekend in CA

It has been an incredibly wet start to the year here in Northern California, and we are in store for another incredible few days through early next week.  Snow reports from Sierra towns and ski resorts since last weekend have been impressive.  I can personally confirm that some of the terrain at Squaw Valley received at least 3′ of fresh snow in the 48 hour period ending on the morning of the 5th.   Local reports here in the central valley exceeded an inch for each of 3 consecutive days (Thanks, CoCoRaHS) and one spot in the Sierra reported 60″ of new snow over the same period.  In addition to all that moisture, it looks like more is on the way.  NWS is forecasting a 70% chance of at least an additional 30″ of snow (their highest category) in the Sierra and another 2″ of rain for here in Davis.  Stay dry, my friends.

AGU Fall Meeting 2016 Review

I thought I would mention what I thought was a notable trend at this year’s AGU Fall Meeting. As atmospheric science has shifted its focus away from meteorology and toward a more basic understanding of the complex physics of our atmosphere, we have developed a variety of unique tools (think general circulation models and satellites aimed as retrieving scientific quantities). But for a long time, we did not utilize these tools to their fullest capabilities. Recently, and this was on full display at AGU this year, we, as a community, have done a much better job of using these tools in a much more systematic way than ever before. I saw more talks and posters than in any previous year that did a great job of analyzing data in a methodical way. I think we’re seeing a maturation of our science. If the conference was any indication, 2017 is going to be a year full of compelling results. I’m looking forward to it.

Going, Going, GOES-R

I have to admit to not being much of a GOES user.  Most of what I do doesn’t depend much on the kind of data we have traditionally gotten from geosynchronous satellites.  But, I am excited for the GOES-R launch tomorrow.  Assuming everything goes as planned, the Atlas rocket carrying GOES-R will lift off from its pad in Florida and carry the satellite out to an orbit 36,000km above the equator where it will officially become GOES-16.  From there, GOES-16 will start taking pictures of Earth in incredibly fine detail, mapping lightning, measuring activity on the sun, and in Earth’s magnetic field.  This data will form the backbone of a new generation of American Earth/Space/Sun weather observations.  Godspeed, GOES-R!

When is a River a River?

Northern California is currently in the midst of its first significant rainfall of the season.  The plume of moisture currently advecting on shore can be traced all the way back to a weakened typhoon in the western Pacific.  I’ve heard a lot of chatter that this is an example of an “atmospheric river“, a strong, steady plume of moisture advected poleward out of the moist tropics.  We have come to appreciate recently that atmospheric rivers are responsible for many of the significant rainfall events here in California and on the western coasts of several continents.   But, I have to ask myself when an atmospheric river is really an atmospheric river and when it isn’t.    The TPW loop shows that this moisture is not arriving from the deep tropics, but rather, from a ex-tropical system.  The original definition of an atmospheric river makes no mention of the origins of the moisture, and as such, it is perfectly general.  But, the connotation has generally been one in which the moisture originates from the TPW maximum around the equator.  The precise definition becomes important as those of us in CA focus research efforts on the formation mechanism of atmospheric rivers and try to determine how they will change under global warming scenarios.  Therefore, I would like to propose that “rivers” such as the one currently impacting CA simply be grouped in with normal warm frontal processes and we reserve the use of “atmospheric rivers” to those features extracting moisture directly from the deep tropics.

ICON GCM RCE A-OK

I wanted to mention one thing about a recent paper which used the ICON general circulation model to simulate states of radiative convective equilibrium over ocean.  The authors ran the model on 5 different domains of varying total area.  The largest simulation was 256 times larger than the smallest.  That’s an impressive range!  The authors convincingly show that the domain size affects many aspects of the simulated atmosphere, but the one I want to mention is the physical morphology of the aggregated, high moisture regions (their figure 6).  The larger the domain size, the more structure there is in the moisture field.  I’ve done a lot of work recently on the links between total moisture and cloud behavior, and I can say that all that variation in the moisture field is critical for clouds.  We convective theorists have based a lot of recent thinking about the interaction of convection with it’s environment on the results of RCE simulations, but very few people have thought about the sensitivity of these ideas and theories to basic simulation properties (like domain size or shape) on the kinds of scales these authors do.  I agree with the authors that their results suggest a few new avenues of inquiry that could be rather revealing.

Source: Radiative convective equilibrium as a framework for studying the interaction between convection and its large-scale environment – Silvers – 2016 – Journal of Advances in Modeling Earth Systems – Wiley Online Library

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