With funding from CPO’s Atmospheric Chemistry, Carbon Cycle, & Climate (AC4), researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory sought to understand why some marine stratocumulus clouds form “open cells” while others form “closed cells,” even when the background whether conditions are similar.
Published in the Geophysical Research Letters, the research was led by Mikhail Ovchinnikov. According to the paper description, the research is important in climate models because closed cell cloud formations are more reflective and therefore reflect a greater percentage of sunlight back to space. If the underlying processes governing the cloud state can be identified, this information can be used to better predict the marine stratocumulus clouds in climate models. The researchers found that the ratio of timescales from two processes play an important role. If the time for rain generation is shorter than the time spent by air ascending in a cloud, rain starts falling out of the cloud, which depletes the cloud water before the air reaches the cloud top. This leaves less water in the air to sustain a widespread cloud deck and open cells tend to form.
Likewise, for clouds with longer rain formation timescales than the time air spends rising in a cloud, closed cells tend to form because more water is available to maintain large horizontal areas in a cloudy state, which would be the conditions for a closed cell formation. This simple conceptual framework works surprisingly well when compared with available observations.
To view online, visit: http://onlinelibrary.wiley.com/doi/10.1002/grl.50810/abstract and to access a full copy of the text, visit: http://onlinelibrary.wiley.com/doi/10.1002/grl.50810/pdf.
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