Campaign : Spring Cloud IOP

2000.03.01 - 2000.03.26

Lead Scientist : Gerald Mace

For data sets, see below.

Summary

The Atmospheric Radiation Measurement (ARM) Program conducted a Cloud Intensive Operational Period (IOP) in March 2000 that was the first-ever effort to document the 3-dimensional cloud field from observational data. Prior numerical studies of solar radiation propagation through the atmosphere in the presence of clouds have been limited by the necessity to use theoretical representations of clouds. Three-dimensional representations of actual clouds and their microphysical properties, such as the distribution of ice and water, had previously not been possible because instrumentation appropriate to the task was not available.

Recent development of improved lidar and radar capabilities by ARM were hypothesized to permit measurements over time that would permit an accurate "representation" of the "real" 3-dimensional cloud field. The IOP observational capability included the standard set of instruments at ARM's Southern Great Plains site as well as a special set of temporary lidars and radars. Aircraft data taken during the IOP supplemented the ground-based remotely sensed data.

Validation of TERRA Satellite: The IOP also served the interests of National Aeronautics and Space Administration (NASA) in its efforts to validate data from the recently launched TERRA satellite. TERRA is the first of the long awaited Earth Observing System (EOS) primary satellites. NASA scientists were members of the IOP planning team and are using the IOP data, combined with data from overflights by NASA's ER-2 aircraft, in the Terra validation effort.

ARESE II Overlap: The Cloud IOP also overlapped with the ARM/Unmanned Aerospace Vehicle (UAV) Enhanced Shortwave Experiment (ARESE) II, also being conducted over the Southern Great Plains site. Throughout the IOP period, efforts were coordinated with the ARM/UAV Twin Otter aircraft. In addition to its own ARESE II missions, the Twin Otter flew four missions in direct support of the objectives of the cloud IOP, contributing valuable radiometric and in situ data to the IOP. The IOP began on March 1 and ended on March 26. Near ideal cloud conditions permitted substantive data sets to be acquired on 10 days during the IOP.

In all, 12 IOP flights were made by the University of North Dakota's Cessna Citation aircraft. While a great deal of analytical work remains to be done, all preliminary evidence suggests that the IOP produced a robust data set that addresses all primary and most secondary scientific objectives of the IOP. Pure ice clouds (cirrus), cirrus clouds transitioning to high-level water clouds (altostratus), and high-level and low-level pure water clouds were all captured and documented. In all cases, ground-based radars and lidars, both permanent and temporary, operated nearly flawlessly, providing an excellent and unprecedented data set.

Description

Scientific hypothesis: The statistics of the radiative forcing within a mesoscale model grid box are quite sensitive to the three-dimensional (3-D) structure of hydrometer properties within the grid box. In an operational sense, ARM is limited to observing the vertical profile of clouds as they advect over the Central Facility (CF) and must, therefore, approximate the 3D structure of cloud within a gridbox by inference. Our working hypothesis is that simple approaches to this problem are sufficient in certain meteorological circumstances and not in others.

Approach to test hypothesis: In order to validate/justify/improve our methodology for generating such inferences, we will deploy a fleet of vertically pointing and scanning lidars and millimeter radars within a mesoscale region around the CF where the 3-D structure of cloud fields will be intensively measured during a multi-week period.

Preliminary Deployment plan: We would like to deploy a nested array of remote sensors with the scanning radars and lidars stationed at the CF and the vertically pointing systems distributed in a triangle away from the CF. This would depend on the cloud field, but in general two radars at the CF would scan in orthogonal planes (along and across the wind) as would the lidars. A triangle would have vertices at Billings, Tonkawa and Lamont (roughly 25 km on a side). A larger triangle might be desirable in addition to or instead of the smaller with vertices at Ponca City (I volunteer for that one), Medford and Garber or Enid (roughly 70 km on a side). We should discuss the relative merits of the array size and orientation. I personally see limited use in going out much farther than 75 km with the limited number of radars and lidars we have at our disposal. We could probably live with a single radar and lidar scanning at the CF but that would compromise the data set integrity in my view. At least three radars are needed for the vertices of a triangle.

Additional Information

Cloud IOP Data Report

The Cloud IOP overlapped with the ARM/Unmanned Aerospace Vehicle (UAV) Enhanced Shortwave Experiment (ARESE) II, also being conducted over the Southern Great Plains site. Throughout the IOP period, efforts were coordinated with the ARM/UAV Twin Otter aircraft. In addition to its own ARESE II missions, the Twin Otter flew four missions in direct support of the objectives of the cloud IOP, contributing valuable radiometric and in situ data to the IOP. The IOP began on March 1 and ended on March 26. Near ideal cloud conditions permitted substantive data sets to be acquired on 10 days during the IOP.

Counterflow Virtual Impactor Results (CVI)

A counterflow virtual impactor (CVI) was flown on the University of North Dakota Citation aircraft in support of the Spring 2000 ARM IOP. The CVI first separates droplets or ice crystals larger than about 8-mm aerodynamic diameter from interstitial aerosol and gases by impaction, then evaporates the droplets or crystals within a dry nitrogen sample stream. Water vapor and residual particle number concentration are measured downstream with a Lyman-alpha hygrometer and condensation nucleus counter, respectively. From these measurements, cloud condensed water content (CVIcwc) and number concentration (CVInum) are determined. CVInum may be artificially enhanced due to breakup of large (>100 micron) droplets or ice crystals in the inlet of this CVI. Therefore, CVInum is not included in this data set for cirrus clouds or stratus clouds containing drizzle.

The CVI was operated successfully on all 12 Citation research flights. Data from these flights have been submitted to the project data archive; see the Readme file for more information. Lagrangian spiral descents on some flights led to particularly interesting data sets. On a few flights, notably Mar12b, very high water contents led to saturation and hysteresis problems with CVIcwc. On Mar18b, heavy icing degraded data quality. Data from all other flights appears to be of high quality. Comparisons of CVI cirrus ice water content with ice water contents calculated from 2-D probe data using CPI crystal habit information have yielded excellent agreement; some of these comparisons have already been included in a submission to the Journal of Oceanic and Atmospheric Technology (Heymsfield et al. 2000). Further comparisons with other airborne and ground-based instruments are anticipated and encouraged (contact Cynthia Twohy at twohy@oce.orst.edu). Pennsylvania State University MMCR Summary

The Pennsylvania State University millimeter-wave cloud radar (MMCR) was transported to the SGP site for the March 2000 cloud IOP. The goals of the deployment were two-fold: generate traditional radar Doppler moments at an ancillary SGP CART site location in support of obtaining cloud radar data over a relatively large spatial domain and collect high-time resolution raw radar output signals in support of studies that attempt to separate cloud droplets from precipitating drops.

Due to a transmitter tube failure, the researchers were unable to generate any useful data during the first three-quarters of the cloud IOP. When the transmitter tube was replaced during the last one-quarter of the experiment, they were able to collect some data, but the overall system sensitivity of the radar was poor. Radar I and Q voltage time series data are available for March 17, 18, and 19 for select periods of time during the occurrence of low-level stratus. The researchers have not made these data sets available to the DOE ARM archive because they are both quite voluminous and of marginal quality. Overall, they were not successful in accomplishing the objectives of their first research goal.

The poor quality of the millimeter-wave radar I and Q voltage time series also prevented the researchers from pursuing the objectives of their second research goal. In this case, however, they have been able to pursue fulfilling the objectives of this goal in the time since the March 2000 cloud IOP. Since the radar was not working properly during the IOP, the researchers did not generate the immense data set that they expected and the researchers ended their deployment early. Both of these turn of events resulted in their contract funds being saved.

With permission from PNNL, the researchers combined these funds with matching funds from Pennsylvania State University to buy an inexpensive, but fast, radar signal processor. They configured this processor so that it was capable of collecting data from the ARM SGP MMCR, and in the summer of 2001 they deployed this processor to the ARM SGP CART site. With the help of Ken Moran, they verified that the processor can be operated on the ARM SGP MMCR without generating interference. The goal now is to collect high-time resolution raw radar output signals from the ARM SGP MMCR to advance studies on separating cloud droplets from precipitating drops in the volume of space above the radar. This is an on-going activity that has emerged as an important one for the research supported by the DOE ARM Grant DE-FG02 90ER61071, as deployment of the new DOE-supported processors capable of processing radar raw I and Q voltages has been delayed approximately one to two years.

Other Contacts

Doug Sisterson, SGP CART Site Program Manager Marv Wesely, ARM SGP Instrument Team Leader Dan Rodriguez, Data and Science Integration Team (DSIT) Contact

Campaign Data Sets

Campaign Participant	Data Set	Archived Data
Albrecht, Bruce	Radar	Order Data
Barnard, James	MFRSR	Order Data
Cairns, Brian	RSP data	Order Data
Flynn, Connor	MPL	Order Data
Flynn, Connor	Ceilometer	Order Data
Heymsfield, Andrew	PMS	Order Data
Lawson, Paul	Lear Jet	Order Data
Liljegren, James	MWR	Order Data
Liljegren, James	MWRP	Order Data
Liu, Guosheng	Liu_cloud_ice_water	Order Data
Long, Chuck	RSR	Order Data
Long, Chuck	TSI	Order Data
Murcray, Frank	ASTI	Order Data
Poellot, Michael	Citation A/C	Order Data
Sekelsky, Stephen	CPRS	Order Data
Tooman, Tim	WSI	Order Data
Twohy, Cynthia	CVI	Order Data