Current Projects

Here are descriptions of some current on-going projects. It’s meant to convey some idea as to the types of things we work on, rather than being an exhaustive list. A lot of this work involves collaboration with other research groups, of which I’ve identified a few in each category, again not meant to be a complete list.

Cumulus clouds

We have participated in a couple of field projects (RICO and GoMACCS) looking at cumulus clouds. Our over-arching goals are to understand the life-cycle of such clouds, and thereby learn how they affect present and future climate. RICO sampled trade wind cumulus in the vicinity of Antigua and Barbuda, mainly under clean aerosol conditions. We’re interested in a number of questions, such as how these warm clouds form rain. During GoMACCS, we sampled mainly non- precipitating clouds around Houston, TX, where the aerosol environment ranged from moderately clean to unbelieveably polluted. We’re looking at how these clouds behave under these different aerosol regimes. Initially, we’re thinking about how buoyancy and entrainment mixing might depend on aerosol Key collaborators: Graham Feingold and Hongli Jiang, NOAA; Seinfeld and Flagan research groups, Caltech; Sonia Lasher-Trapp, Purdue.

This trade cumulus cloud is the poster-child for RICO.

Stratocumulus clouds

We have also participated in a couple of projects focused on stratocumulus clouds (MASE-1 and -2), which have the greatest impact on the Earth’s radiative budget and therefore are climatically interesting. Our backyard (or is it frontyard?) happens to be one of the great places to sample stratocumulus, so we are typically based at CIRPAS in Marina, CA, just 35 miles south of Santa Cruz and fly missions onboard their Twin Otter. At the moment, we’re focused on understanding the characteristics and formation of drizzle in stratocumulus, since it’s a poorly-understood process, but one that is potentially critical to the water budget and therefore life cycle of cloud-topped marine boundary layers. An upcoming project (POST) will focus on the nature of entrainment at the tops of stratocumulus decks. Key collaborators: Seinfeld and Flagan research groups, Caltech.

View of the California coast from above the stratocumulus-topped ocean, with the CIRPAS Twin Otter wing visible as well.

Cloud condensation nuclei

Cloud condensation nuclei or CCN are those particles which serve as the nuclei for cloud drop formation. This subset of atmospheric particles thereby links particulate air pollution to cloud properties, leading to a variety of putative connections between human-generated aerosols and climate, a.k.a. aerosol indirect effects. We are specifically interested in mechanisms governing the growth rate of CCN by condensation of water vapor, which has been hypothesized by many to be potentially slower than for pure water drops in the presence of, e.g., organic films or slowly dissolving compounds. We have designed and built an instrument to directly examine this process, and have taken it to a variety of locations around the country. Lately, we’ve done some very fruitful sampling in Ben Lomond, which is in the mountains just above Santa Cruz. Key collaborators: Thanos Nenes, Georgia Tech.

A view of our trailer at the ARM Southern Great Plains site.

Aerosol Iron and Biogeochemistry

Iron is a key trace nutrient in the open ocean, and is generally believed to be the key limiting nutrient in the so-called high nitrogen low chlorophyl (HNLC) regions of the world’s oceans. The normal view is that the deposition of new iron to these areas is dominated by windblown dust from continents. However, we’ve recently shown that in the atmospheric outflow from Asia, soluble iron, which we use as a proxy for bioavailable iron, appears to be most strongly related to combustion processes, and in particular, coal combustion. This changes the normal paradigm, and leads to a new pathway by which human activities can alter the carbon cycle, i.e. the biological pump of CO2. We’ve been extending this work using global models to study the importance of this new soluble iron source over larger spatial and longer temporal scales. Key collaborators: Jamie Schauer and group, Univ. Wisconsin-Madison; Natalie Mahowald and group, Cornell University; Nicholas Meskhidze, NC State.

A view of the Kosan, Korea supersite during the ACE-Asia field campaign where we studied Asian dust and pollution aerosols.

Instrumentation

Developing new instrumentation is a necessary step in some of our research activities. Although it can be a challenging activity, the rewards are almost always worthwhile – the new data that a novel instrument yields is often critical to new understanding. We’ve been working with Artium Technologies in Sunnyvale, CA, who are world leaders in the technique of phase Doppler interferometry (or PDI) to develop cloud and aerosol instrumentation. These new instruments have been crucial to our ability to make scientific progress in these areas. Key collaborators: Raymond Shaw and group, Michigan Tech.

The Artium Flight PDI instrument that we helped develop for making new and improved cloud drop measurements.

Last Updated: January 4, 2008