UC Santa Cruz @ VOCALS?

• PI: Patrick Chuang• Instrument: Phase-Doppler

interferometer• Measures cloud drop

– size– velocity – inter-drop spacing

on a single drop basis.• Size range: 3 to 150 um

PDI mounted on the CIRPAS TwinOtter

Pre-flight testing of the PDI

Sample data from the Marine Stratocumulus Experiment (MASE). Note the occurence of bi-modal distributions most likely caused by collision-coalescence, a key process in drizzle formation.

Example of bimodal distribution in stratocumulus clouds.

Comparison of view volume diameter derived from in situ measurements and theoretically-derived curve.

The theoretical curve uses two parameters:

1. The laser beam waist diameter

2. The minimum scattered light intensity required for detection by photodetectors.

Fitting data to theoretical curve retrieves (1), leaving (2) as the only free parameter.

Comparisons of PDI and Gerber derived LWC.

(A) No roll-off correction applied to Gerber data.

(B) Normal roll-off correction.

(C) Roll-off shifted by 7 um (towards smaller sizes)

(D) PDF of 1 Hz LWC data during MASE.