EPCAPE-SCARPE

Stratiform Cloud Analysis of Radiative Properties

15 February 2023 - 15 February 2024

Lead Scientist: Dan Lubin

Observatory: AMF (ARM Mobile Facility 1) - EPC

This program will deploy a set of spectral filter and broadband radiometers with EPCAPE at the Mt. Soledad site, with three objectives: (1) determine the response in cloud radiative properties to changing cloud microphysics under changing aerosol regimes; (2) explore the potential for simple and low-cost radiometers to provide data that are sensitive to both cloud liquid water path (LWP) and droplet effective radius (re); (3) obtain radiation measurements within low-level stratiform clouds for comparison with below-cloud measurements from similar ARM-Facility radiometers on Scripps Pier. The instruments are owned by Scripps as part of a suite called Clouds and Climate – Remote Integrated DEployement of Radiometers (CC RIDER) and comprise two Eppley precision spectral pyranometers (PSP) covering 280‑2800 nm, an Eppley PSP with a long-pass near-infrared filter covering 780-2800 nm, an Eppley pyrgeometer covering 4-50 microns, and an Eppley total ultraviolet radiometer (TUVR) covering 295‑385 nm. All irradiance data will be recorded continuously in one-minute averages. The CC RIDER will be co-located with an ARM microwave radiometer (MWR) that will provide independent observations of LWP. Combinations of MWR and multispectral shortwave radiation measurements have been proven by ARM/ASR researchers to provide useful simultaneous retrievals of LWP and re. Our hypothesis is that similar retrievals might be possible with the CC RIDER alone, as (1) the TUVR is sensitive only to cloud‑scattering optical depth, (2) the near-infrared PSP is especially sensitive to cloud droplet size, and (3) the other PSPs and PIR can provide radiative closure. The challenge is that without an independent LWP measurement, cloud optical depth is much less sensitive to changing re and large samples may be required for statistical significance. But if successful, this method might be applicable at other ARM facilities: CC RIDER has a small footprint and is entirely solar powered. More generally, the SCARPE data will be a resource for aerosol-cloud interaction studies, particularly those involving the aerosol measuring equipment on Mt. Soledad.