Cloud Layer Experiment (CLEX-5)


The Cooperative Institute for Research in the Atmosphere's (CIRA) DoD-sponsered Center for Geosciences/ Atmospheric Research (CG/AR) recently completed the fifth in an ongoing series of field programs connected with the Cloud Layer Experiment (CLEX). The motivation for CLEX is to further our understanding of the processes inherent to the formation, maintenance and dissipation of mid-level, non-precipitating mixed phased clouds. A better understanding of mid-level clouds has many applications for both military and civilian purposes. For example, during DESERT SHIELD/STORM, mid-level cloud systems often masked target areas and hampered use of electro-optic sensors and weapons systems. For civilian pilots, poorly forecast mid-level clouds often restrict flight visibility and can create icing hazards. Of further interest is possibly improving model initialization, determining impacts to regional dynamics (such as radiative forcing effects), and understanding climatological forcing by mid-level cloud on the Earth Radiation Budget.

SCIENTIFIC OBJECTIVES OF CLEX-5:

-Determine Microphysical, Radiative and Dynamic (MRD) Structure of a Typical Mid-latitude, Mid-level, Mixed-phase Cloud System

-Find Main Processes that Create or Impact MRD Morphology

-Ascertain Important Factors Affecting Cloud Lifetime

-Develop Criteria for Categorizing Cloud Type and Structure

-Devise a Reliable Means to Characterize Mixed-Phase Cloud Properties with Satellite Sensors. Focus on 3.9 micron Channel.


PMS probes over 4 Dec 1999 cloud field.


CLEX-5 Field Campaign:

Most of the microphysical measurements collected during CLEX-5 were obtained aboard the University of North Dakota’s Citation II research aircraft. The basic instrument package included measurements of temperature, dewpoint temperature, pressure, and cloud microphysics, along with aircraft position, attitude, and performance characteristics at a 25 Hz data rate. The aircraft also carried Eppley pyrgeometers and pyranometers to measure the upward and downward shortwave and longwave broadband fluxes, and a forward-looking video camera to monitor visual conditions. For our study, we focus on the cloud microphysical measurements, which were made with an array of Particle Measuring System (PMS) probes at a 4 Hz data rate, and a Cloud Particle Imager (CPI). The PMS probes include the Forward Scattering Spectrometer Probe (FSSP), one-dimensional (1D-C) and two-dimensional (2D-C) optical array imaging probes, and the King Liquid Water Probe.

The 12 Apr 2000 flight took place aboard a Learjet leased by Stratton Park Engineering Company (SPEC). This aircraft had the same basic instrument package as described for the Citation II, including PMS and King probes, CPI, temperature, and altitude sensors. In contrast, however, the Learjet did not carry pressure or wind instruments, and data was recorded at the slower rate of 1 Hz.

The CLEX-5 field campaign ran from 4 Nov 1999 through 6 Dec 1999 with two extra CLEX-5 missions run on 10 Mar 2000 and 12 Apr 2000. Below are links to successful CLEX-5 observations days. 



CLEX-5 Operations Days:

        02 Dec 1999

        04 Dec 1999

        05 Dec 1999

        10 Mar 2000

        12 Apr 2000

Link to aircraft data