Using the 1000 most common words

The soft, white things made of water in our sky can help cool the blue and green ball we live on by kicking the sun light back to space. I study whether these soft, white things in the sky will stick around or die away if there are more tiny bits in the air. Because rain usually kills the soft, white things, I fly through the soft, white things to study whether more of the tiny bits make water drops smaller to form less rain and keep the soft, white things around.

The work on precipitation susceptibility attempts to get at the question: Can the concentration of aerosol particles in the air affect precipitation rates in marine stratocumulus? We currently don't have a clear understanding of what increased numbers of aerosol particles will do to rainfall in clouds. Much of the response looks to depend on the type of clouds, so we've concentrated on looking at the response in low-lying liquid clouds. This understanding will hopefully be helpful in assessing results from regional model simulations that are starting to incorporate the effect of aerosols on clouds. To get at the effect of aerosol concentrations on marine stratocumulus clouds, we look at correlations between precipitation rates and the concentration of ambient aerosol particles with diameters greater than 0.1 micrometer.

The current understanding of the effect of aerosols on precipitation is that an increase in aerosol concentration leads to more numerous and smaller cloud droplets. This slows down the rate at which cloud droplets collide with each other to form drizzle drops. In short, less rain is expected with increased concentrations of aerosol particles.

Evidence supporting this hypothesis, which pertains only to clouds with liquid water droplets, is found in observations from past field experiments, but quantifying the sole effect of aerosol particles has always been difficult. Changes in aerosol concentrations coexist with changes in meteorology, such as changes in thickness of clouds.

Our study tries to account for the meteorology by grouping the clouds by cloud thickness and looking at the relationship between aerosol concentrations and rain rate in each group. When we group the clouds by their thickness, we find that the effect of aerosols on the precipitation varies with the thickness of the cloud. The magnitude of the precipitation response decreases with increasing cloud thickness. We argue that most of the variation exists because in thinner clouds, aerosol concentrations can determine whether it drizzles or not, while in thicker clouds there is so much cloud water that it drizzles regardless of the aerosol concentration.

More details can be found in our paper below.

In this study, we looked at cold pools that were observed over the southeast Pacific Ocean. The cold pools form from the evaporation of drizzle under precipitating marine stratocumulus clouds. Using data from the research flights of the NSF/NCAR C-130 flown during VOCALS, we documented the environment and conditions in which we observed the cold pools. We also looked at the thermodynamic, dynamic, and chemical characteristics associated with the cold pool air mass. The abstract and paper can be found in the link below.

One of the main objectives of the VOCALS field program was to make measurements within pockets of open cells (POCs). I examine measurements from five different POC cases that were sampled by the C-130 with the aim to identify the key microphysical and macrophysical cloud processes that occur within POCs. Initial work has involved looking at the mean cloud characteristics to estimate the sink rate for aerosols within POCs.