309 Boundary Layer Kite Observation and Implications for Shallow Convective Cloud Development

Wednesday, 11 July 2018
Regency A/B/C (Hyatt Regency Vancouver)
Alison D. Nugent, Univ. of Hawaii at Mānoa, Honolulu, HI; and D. DeCou

Kite-based platforms have been used for centuries to measure atmospheric properties. With rapid development of new technology in recent years, kite measurement can also get a makeover. We use our strategic location on the island of Oahu in Hawaii to make meteorological measurements from the windward coast using a kite fitted with instrumentation lofted by the steady trade wind flow. Incoming marine air is measured from the coastline before it is lifted and modified by the island, giving us information on upwind flow properties with application to two areas of cloud physics relating to shallow convective clouds developing over an island mountain.
The first area is observation of sea-salt aerosols, also known as Giant Cloud Condensation Nuclei (GCCN), which act as extremely efficient cloud nuclei. Because of their large size, hygroscopicity, and salt content, GCCN have been shown to rapidly grow by condensation. Ultimately, GCCN help to broaden the droplet spectrum, and can accelerate precipitation initiation in warm clouds. For this reason, the GCCN size distribution is important to quantify, but observing it is difficult. In ambient conditions, GCCN are always wetted, making it especially hard to quantify salt mass. Currently the best way to sample the GCCN size distribution is the Giant Nucleus Impactor (GNI) onboard the NSF/NCAR C-130 aircraft. Here we discuss a new method to sample the GCCN size distribution using the same technology as the GNI, but deployed on a kite. The “Mini-GNI” device exposes slides to the free airstream, GCCN impact onto the slide, and are later analyzed in a lab. We will discuss our recent work with regards to the Mini-GNI as well as preliminary results and implications for shallow convective cloud development over the island.
Second, our kite-tethered instruments also measure atmospheric properties including temperature (T) and moisture (qv) variations. Prior work has shown that regions with T and qv variations tend to have neutral buoyancy, observed via constant virtual temperature, and may act as “seeds” of convection as air is lifted. By quantifying variations of T and qv in the sub-cloud marine layer, we make inferences about the scale and convective strength of shallow convective clouds over the island.
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