Atmospheric Sciences



(3:00 SLAB Seminar Room, unless stated otherwise)

Jan 09 (Tuesday, 11:00): Dr. Joshua Willis (NASA JPL)

"OMG, It’s Melting. Early Results from Oceans Melting Greenland (OMG), and the Use of Comedy to Communicate About Climate Change"

Not Funny: Oceans Melting Greenland (OMG) is an airborne NASA Mission to investigate the role of the oceans in ice loss around the margins of the Greenland Ice Sheet. A five-year campaign, OMG will directly measure ocean warming and glacier retreat around all of Greenland. By relating these two, we will explore one of the most pressing open questions about how climate change drives sea level rise: How quickly are the warming oceans melting the Greenland from the edges?

This year, OMG collected its second set of both elevation maps of marine terminating glaciers and ocean temperature and salinity profiles around all of Greenland. This give us our first look at year-to-year changes in both ice volume at the margins, as well as the volume and extent of warm, salty Atlantic water present on the continental shelf. In addition, we will compare recent data in east Greenland waters with historical ocean observations that suggest a long-term warming trend there. Finally, we will briefly review the multi-beam sonar and airborne gravity campaigns—both of which were completed last year—and their impact on bathymetry maps in the coastal waters around Greenland.

Funny: The first time I showed a funny slide at AGU, it bombed. Badly. “What causes global warming?” I asked an audience of 100 learned colleagues. I pushed the space bar. Up popped a photo-shopped picture of a gigantic Al Gore breathing fire on the Earth….

Silence. Complete silence. Even the crickets were judging me.

Since then, I’ve completed an entire curriculum at a world-renowned school of funny (The Conservatory Program at Second City, Hollywood), written sketch shows, told funny stories, acted in short and full-length feature films, and practiced. Mostly practiced. A lot. So, did I get better at making global warming funny? Come find out.




Feb 07: Dr. Honghai Zhang (Princeton University)

"Robustness of Anthropogenically Forced Decadal Precipitation Changes Projected for the 21st Century"   

Precipitation is characterized by substantial natural variability, including on regional and decadal scales. This relatively large variability poses a grand challenge in detecting anthropogenically caused precipitation changes. Here we use large ensembles of climate change experiments with multiple climate models to demonstrate that, on regional scales, anthropogenic decadal changes in ensemble-mean precipitation (i.e., mean state) are detectable, where “detectable” means the change is outside the range expected from natural variability. Relative to the 1950-1999 period, simulated anthropogenic shifts in precipitation mean state for the 2000-2009 period are already detectable over 36-41% of the globe—primarily in high latitudes, eastern subtropical oceans and the tropics. Anthropogenic forcing in future medium-to-high emission scenarios is projected to cause detectable shifts over 68-75% of the globe by 2050 and 86-88% by 2100. Our findings imply detectable anthropogenic shifts in precipitation mean state over the majority of the planet within the next few decades.

Feb 14: Dr. Brian Mapes (RSMAS)

"Professor Grumpy Fiiiinally Swallows the Open-Source Nexus Lingo; Teaching, Research, Comms & Collabs are Transformed!"

In this seminar, I will attempt to convey my newfound enthusiasm for a fantastic nexus of free software for highly collaborative computing: {Jupyter + iPython + GitHub}. I am dizzily imagining whole curricula in this space, perhaps displacing books. My whole research workflow will now be in Jupyter. It’s even a communication vehicle: In addition to being a computational code, a Jupyter notebook can also be both an eye-friendly formatted document with math and text and hyperlinks (as well as the code and its resulting figures), and furthermore a slide show! And it is all naturally collaborative — world-shared, mix-and-matchable, yet with traceable contribution histories. If you want to follow along “live”, consider doing these instructions and bringing your laptop. Or, just listen and learn.

Feb 21: Dr. Yoshiaki Miyamoto (RSMAS)

"A Dynamical Mechanism for Secondary Eyewall Formation"

This study proposes that secondary eyewall formation (SEF) of tropical cyclones (TCs) can be attributed to an instability of flow in the free atmosphere coupled with Ekman pumping. Unstable solutions of a 1.5-layer shallow water system are obtained under fast wind speed conditions in the free atmosphere. The instability condition derived in the linear model indicates the importance of the ratio of vorticity to angular velocity, and the condition is more likely to be satisfied when the ratio is large and its radial gradient is positive. In other words, fast angular velocity, low absolute vertical vorticity, small negative radial gradient of angular velocity, and large gradient of vertical vorticity are favorable. Eigenvalue analyses are performed by using a vorticity profile with a secondary maximum with a very small magnitude and a wide range of other parameters.

The growth rate increases with vorticity outside the radius of maximum wind (RMW), the radius of the secondary vorticity maximum, its magnitude, and the Rossby number defined as the ratio of maximum tangential velocity to the RMW multiplied by the Coriolis parameter. Furthermore, the growth rate is positive only between 2 and 7 times the RMW, and it is negative close to or far outside the RMW. These features are consistent with previous observational and modelling studies on SEF. A dimensionless quantity obtained from the unstable condition in the linear theory is applied to SEF events simulated by two different full-physics numerical models. It is observed that the dimensionless parameter increases several hours before a secondary peak of tangential velocity forms, suggesting that the initial process of SEF can be attributed to the proposed theory.

Feb 28: Matthew Igel (University of California Davis)

"The Cloudy Links Between Tropical Bulk-Moisture and Precipitation"

The focus of this talk will be on the two-way relationships between moisture, clouds, and precipitation in the tropics. I will begin by discussing the properties of the tropical moisture distribution and the simple, but highly non-linear, way in which precipitation depends on column moisture. This latter relationship is reproduced in a high fidelity, large domain cloud resolving model run in a state of radiative convective equilibrium. Model output will be used to describe the physical pathways that transform atmospheric bulk moisture into surface precipitation. Then, the vertically-integrated column moisture will be broken down into two contributions separated by the base of the melting layer. These new layer moisture quantities will be shown to relate much more intimately with cloud processes and the distribution of cloud types than column moisture. These layers act independently to result in the non-linear coupling between column moisture and precipitation. This result will be confirmed with a combination of AIRS, CloudSat, and GPM satellite observations. Next, I will introduce a new way to use our understanding of precipitation and bulk moisture to construct a simple data-driven global hydrological model. The model is asymptotically integrable and can be used to examine the possible responses of tropical moisture and precipitation to climate warming. This simple analytic model suggests the ensemble of climate models may not simulate a wide enough distribution of possible hydrological responses. Predictions can be related back to process understanding.

Mar 07: Dr. Kerry Emanuel (Lorenz Center, MIT)

"Severe Thunderstorms and Climate"

Severe thunderstorms, which are often associated with strong winds, hail, and tornadoes, pose substantial threats to people, livestock, and agriculture. While their dynamics are well understood, relatively little is known about how climate change (man‐made or natural) might affect such storms. In this talk I will focus on one of the main environmental prerequisites for severe storms: Convective Available Potential Energy (CAPE), which is a measure of the potential energy stored in moist atmospheres that can be released explosively when the potential energy barrier that permits its accumulation breaks. I will discuss the work of my former PhD student that shows, rather unexpectedly, that CAPE usually accumulates over only the 6‐8 hours leading up to the storm and that its build‐up is strongly controlled by soil moisture. I will present observational evidence for this as well as a very simple theoretical model, and discuss how climate change should affect CAPE and how the new understanding of CAPE may someday allow for seasonal prediction of severe storm activity.

Mar 14: Dr. Igor Kamenkovich (RSMAS)

"Observing System Simulation Experiments (OSSEs) for an Array of Profiling Floats"

Mar 21: Dr. Johnna Infanti (RSMAS)

Mar 28: Dr. Emmanuel Hanert (Louvain-La-Neuve)

Apr 04: Conor Smith (45-Minute AMP Student Seminar)

Apr 11: Dr. Colwell

Apr 18: Juan Pinales (45-Minute AMP Student Seminar)

Apr 25: Alexis Denton (45-Minute AMP Student Seminar)

May 02: Dr. Kerri Pratt (University of Michigan)