2015 CIRA Seminars
Atmospheric researchers have long attempted to untie the Gordian Knot of meteorology — that intractable and intertwined tangle of observational imprecision, theoretical uncertainties, and non-linear influences — that, if unravelled, would provide perfect prevision of the weather for ten days, of seasonal conditions for next year, and of climatic conditions for a decade, a century, a millennium, or longer.
Outstanding student paper ceremony and 100th anniversary celebration of Herbert Riehl’s birth will begin at 2:30 p.m. in the Weather Lab.
Climate change is increasingly being recognized as a growing environmental crisis that must be addressed. Studies have shown that the costs of addressing this problem are much less than the costs of dealing with the consequences. Because the major driver is the emission of greenhouse gases associated with the burning of fossil fuels, the most direct way to address the problem is to rapidly decrease the use of these fuels. This can be done via the adoption of a combination of energy efficiency and carbon-free energy technologies.
The Po Valley is a hot spot for air pollution both for the emission sources due to the intense industrial, agricultural and trading activities and the orography of the Valley, surrounded on three sides by high mountain ranges, that favors the accumulation of particulate and gaseous pollutants in the lower levels of the atmosphere.
In summer 2012, a landfill liner comprising an estimated 1.3 million shredded tires burned in Iowa City, Iowa. During the fire, continuous monitoring and laboratory measurements were used to characterize the gaseous and particulate emissions. In the tire fire plume, we observed significant enrichments in ambient concentrations of CO, CO2, SO2, particle number (PN), fine particulate (PM2.5) mass, elemental carbon (EC), polycyclic aromatic hydrocarbons (PAH), azaarenes (PAH with nitrogen heteroatoms) and aromatic volatile organic compounds (VOC).
In the central and eastern U.S., as well as other continental locations at midlatitudes around the world, warm-season heavy precipitation is most frequent at night.
A growing interest in the potential effects of aerosol perturbations on deep convective clouds has resulted in numerous publications over the past decade. These studies have primarily focused on aerosol-induced changes in updraft strength, precipitation amount, precipitation patterns, and lightning frequency. In this talk, I will highlight the primary mechanisms for aerosol effects on deep convective clouds that have been proposed in the literature.
In this talk I will review the history of thought regarding the formation of tropical cyclones. The conditions required for their formation as presented by William Gray, John McBride, and Raymond Zehr are first discussed, followed by a review of early work by Jule Charney and others. The results of observational programs in the east and west Pacific and theoretical studies in the 1990s are reviewed, including the seminal work of Marja Bister and Kerry Emanuel. These works form the background for the most recent observational and theoretical results, which will be discussed in detail.
The upscale aggregation of convection is used to understand the emergence of rotating, coherent midtropospheric structures and the subsequent process of tropical cyclone formation. The CM1 model is integrated on an f-plane with uniform SST and prescribed uniform background flow. Moist cyclonic vortices form, merge, and eventually result in a single dominant vortex that subsequently forms a tropical cyclone. Consistent with previous studies, the approach to saturation within the midtropospheric vortex accelerates the genesis process.
Climate change represents an enormous challenge for today’s generations. Yet we are thinking too small if we conclude its primary lessons concern greenhouse gases or even energy sustainability. The deeper lesson is about the critical milestone humanity has achieved with the scale of its reach. We can now readily change Earth in its entirety, something civilization has never been able to do previously. Our newfound global-scale reach will fundamentally alter both nature and society, mostly in ways we can barely anticipate.
Before the so-called ‘climate warming hiatus’, the answer to this question seemed certain. But our inability to explain observed changes in surface temperature over the past two decades, and associated sea level rise, ocean heat uptake, and the changes to the planetary energy balance in a physically consistent and connected way has caste doubt on our understanding behind this basic question. In this talk, recent and convincing evidence for where the heat is really going into Earth will be presented, and new insights on understanding the planetary energy balance will be described.
Aerosol particles in the atmosphere adversely affect climate, air quality and health. They interact with incoming radiation by absorbing/scattering light and by acting as condensation nuclei for cloud droplets. Organic material comprises a significant fraction of such atmospheric particulate matter. A large portion of this material is produced by physical and chemical processes in the atmosphere and is referred to as ‘secondary organic aerosol’ (SOA).
New GOES infrared satellite imagery has been developed to continuously monitor changes in the cloud top convective and cirrus canopy structure of tropical cyclones. This satellite imagery has also revealed a curious diurnal pulsing pattern that may represent an unrealized, yet fundamental process of mature tropical cyclones. These diurnal pulses appear as IR "cold rings" in the satellite imagery.
What: 5–10 min intros by individual faculty members
Who: Profs. Collett, Denning, Kummerow, Ravishankara, Rutledge, Schubert, Thompson, van den Heever
Why: provide overview of research areas & groups in the department
Why2: gather for cookies & snacks before and pizza after (in Weather Lab)
2014 CIRA Seminars
Convectively coupled equatorial waves (CCEWs) represent the leading modes of synoptic scale organized convection in the tropical troposphere and they are known to affect weather in both the tropics and midlatitudes. Despite their prominence in the observations, CCEWs are poorly represented in current general circulation models used to predict weather and climate. Because of their implied level of deterministic predictability, it is important to understand the key physical mechanisms underlying their variability in order to improve their model representation.
In response to increasing concentrations of atmospheric CO2, high-end general circulation models (GCMs) simulate an accumulation of energy at the top-of-the-atmosphere not through a reduction in out-going longwave radiation (OLR) as one might expect from green-house gas forcing but through an enhancement of net absorbed solar radiation (ASR). A simple linear radiative feedback framework is used to explain this counter-intuitive behavior.
We consider scattering of light by complex atmospheric particles with carbonaceous, silicate, and icy compositions. First, we pay attention to modeling the particle shapes with the so-called Gaussian-random-sphere and Gaussian-random-ellipsoid geometries, where the undulations on the basic regular shape are described by multivariate Gaussian statistics. Scattering by such particles is studied using next-to-exact (e.g., the discrete-dipole approximation) and approximate methods (e.g., the ray-optics approximation).
Increased resolution in modeling and in observations in the ocean have revealed rich dynamics at O(km) lateral scales in the ocean associated with O(1) Rossby and Richardson numbers. These sub-mesoscale oceanic processes are very different from the quasi-geostrophic dynamics at the large scale and the isotropic mixing at the small scales. They are important in the upper ocean frontal regions and make important contribution to vertical fluxes of buoyancy and tracers in the ocean.
High impact meteorological and hydrological events, such as severe thunderstorms and flash floods, typically consist of phenomenon that occur on temporal and spatial scales that fall into the meso α, meso β, or meso γ range. The associated atmospheric processes involve ageostrophic motions and are often nonhydrostatic, so Numerical Weather Prediction (NWP) models generally show poor predictive skill simulating the phenomenon, specifically the details. Therefore, predicting the beginning, ending, areal distribution, and magnitude of high impact events remains a significant forecast challe
New FAA (NextGen) and NWS (Weather Ready Nation) strategic priorities have resulted in an evolution of the Aviation Weather Center's mission that promotes the use of web services aimed at delivering operational Interactive decision support services. This requires several steps for the AWC which include an easy-to-maintain data back-end leveraging ADDS (Aviation Digital Data Service), formatting the data for efficient and reliable delivery to the browser, better support for domestic and especially internat