CLEX5

The Cloud Layer Experiment (CLEX-5) was held in November 1999. The University of North Dakota Citation aircraft was used to obtain in-situ measurements of the microphysical properties of mid-level, non-precipitating clouds, while at the same time satellites and the CART instruments were used to gain a better understanding of the bulk radiative properties of these clouds.

Scientific hypothesis: The Cooperative Institute for Research in the Atmosphere (CIRA) at Colorado State University is continuing to investigate middle level, complex layered cloud systems under funding from the Department of Defense. This investigation is similar in scope to CLEX-1, conducted at your facility in July 1996, and includes observation of the cloud systems from satellite, aircraft, and surface platforms as outlined below. The surface component of the research will consist of a field observation campaign to provide ground truth for the aircraft and satellite observations. It is the purpose of this document to provide a sketch of the science plan to the ARM science community as background for a formal request to use the CART facilities for the surface observations. As in past collaborations, we propose to share all data collected in CLEX-5 with ARM scientists studying similar features of layered clouds. The requested period of support is from Nov 5 to Dec 5, 1999.

The scientific goals of the task for which logistical support is being requested are centered on a better understanding of the nature and role of middle level (2.0 to 6.0 km), non-precipitating cloud systems. The goals of the current investigation are threefold: first, to develop and test methods for inferring cloud tops and especially cloud bases from satellite observations and supporting observations; second, to study the role of radiative energy transfer in the overall energy budget of these clouds; and third, to analyze the potential for increasing forecasting skill of medium range models by including satellite inferred parameters of middle level clouds in the initial data field. It is noted here that convectively active/precipitating systems are not a focus of this study.

Approach to test hypothesis: The field observation phase of the research will consist of intensified satellite data collection, airborne “in situ” microphysics observations, and the surface component. Satellite data will be gathered from GOES, NOAA, and DMSP platforms by CIRA’s satellite downlink facility at Colorado State University. The basic purpose of the surface component is to provide ground truth of the cloud base (and to the extent possible cloud top), cloud base radiative fluxes and remotely sensed cloud liquid water.

In situ microphysical measurements by the University of North Dakota’s Citation aircraft will provide the following atmospheric parameters:

• Cloud Liquid Water
• Microphysical Distribution Measurements
• Surface State Parameters (Pressure, Temperature, Humidity, Winds, etc.,)
• Mission Scientist Observations
• Cloud Video

The aircraft may also be configured to retrieve some cloud top radiometric measurements. In addition, a separate aircraft carrying an airborne cloud radar may participate, but has not been confirmed at this time. Ideally, your coordination and support will permit the flight patterns to occur over the CART surface instrumentation, providing critical ground truth for the airborne and space measurements.

The final goal of the research will benefit from the data collected by the NOAA wind profiler network surrounding the CART site. These data will contribute to the understanding of how well the medium range forecasts are handling the motion fields that may be associated with the formation and maintenance of the middle level cloud systems.

Activity Summary

An observational study of several mixed-phase, non-precipitating altostratus and altocumulus clouds was recently completed in the CLEX-5 (Complex Layered Cloud Experiment 5 Nov - 5 Dec 1999) field campaign. During this experiment, the University of North Dakota Citation II research aircraft took in-situ microphysical measurements of mid-level clouds over the central and northern Great Plains of the United States. During the IOP, we collected mixed-phase cloud information on four days: 11 Nov and 2, 4, 5 Dec 99. The 11 Nov 99 case was over Central Montana, while the remaining three cases were over the SGF ARM CART Site.

Our goal is to characterize the morphology of mixed-phase clouds in order to begin molding a conceptual picture of their formation, evolution and dissipation mechanisms. We found ice and liquid-water mixed phase conditions in all four cloud systems, ranging in altitude from 2400 up to 7200 m. It is noteworthy that synoptic conditions were different in each! case. Three of the clouds were on the order of 600 m thick, while one case was 1500 m thick. Temperatures varied from a mean of about –7° C to –28.5° C. In two of the cases, liquid water content values were approximately 0.005 to 0.05 g/m3, while the remaining two cases had higher values in the 0.05 to 0.15 g/m3 range. Upward vertical motion was positive for the higher liquid water cases, and tended towards negative values on the days when we measured lower amounts.

We have compared our preliminary measurements to those obtained in previous studies of this cloud type by several authors (Heymsfield, et. al., 1991; Hobbs and Rangno, 1985, 1998; Paltridge, et.al., 1986; Pinto, 1998; and Tulich and Vonder Haar, 1998). Observations of cloud temperature, height, liquid water content and vertical wind field from these studies generally showed very good agreement with the CLEX-5 measurements.

Timeline

Campaign Data Sets