Cloud IOP

27 April 1998 - 17 May 1998

Lead Scientist: Gerald Mace

Observatory: SGP

The Spring 1998 SCM/Cloud IOP was conducted from 27 April to 17 May 1998 at the ARM SGP site. All objectives outlined in the planning document were addressed to some degree. As is typical of mid-spring in Oklahoma, the meteorology was quite varied ranging from cold rain to severe thunderstorms to clear and hot. The majority of the period was clear, however.

The goals of the IOP included:

  • Intensive observations of cirrus clouds with in situ aircraft and surface-based and space-based remote sensors
  • Resolution of MMCR calibration uncertainty
  • In situ sampling of airborne insects that are causing non-cloud echoes in the MMCR radar data. (Summary of CU Kite-Borne Activities (Insect Studies) (pdf file))

In the following paragraphs, we will discuss the accomplishments in each of the above items.

Intensive Cloud Observation Periods: As mentioned above, the majority of the IOP period was relatively clear although several very interesting events were sampled. Surface observations during the IOP were augmented by the University of Mass. Cloud Profiling Radar System (CPRS), the University of Utah millimeter cloud radar (see image below) and Polarization Diversity Lidar (PDL - PDL data were collected from 8 May), and the Hemispheric Sky Imager. Additionally, the Penn State group collected raw voltages from the MMCR. The unaveraged voltages allow calculation of arbitrarily high velocity resolution Doppler spectra.

29 April - Liquid-phase boundary layer clouds: The University of North Dakota (UND) Citation flew ramps and spirals over the CART site in single and multi-layer boundary layer clouds. Aircraft observations showed regions of quite high (1g/m3) liquid water content. 2 May - Thunderstorm Anvil Cirrus: The progression from optically tenuous to quite thick cirrus detrained from thunderstorms were sampled by the UND Citation. This event coincided with two overpasses of the Tropical Rainfall Measurement Mission (TRMM) satellite. The figures below show sample data from this event. 8 May - Orographically generated cirrus transitioning to anvil cirrus (2 flights): The Citation performed steps and spirals through cirrus that appeared to form downwind of the Rocky mountains in New Mexico. Bullet rosettes and a 22o Halo were observed. This layer became mixed with convective cirrus during the afternoon. The second flight sampled the convective cirrus and included a 100 km turbulence leg and finished with legs over the CART site in the ragged cloud base (possibly mammatus). 14 May - Cirrus over a lower stratiform layer: A 3 km deep cirrus layer as sampled by the Citation. Cirrus was patchy with a persistent stratiform undercast.

A total of 21 aircraft hours were used including ferry time and a calibration flight. All instrumentation worked well except for the LiCor dewpoint sensor on 4/29, the ozone monitor on 4/29, and the inertial navigation system toward the end of the flight on 5/14. Notable was the exceptional performance of the cryogenic frost point hygrometer that failed briefly only twice during the climb out on two flights. Additional information can be found at the Desert Research Institute www site.

In Situ Sampling of Airborne Insects: Using a remotely operated capture device (See figure left) developed by Dr. Ben Balsley and flown from a tethered blimp and parafoil kite, insects were collected between the surface and 700 meters above ground level during several days of the IOP. The samples were photographed (See figure left), frozen and sent to Dr. John Westbrook of the USDA at Texas A and M. While analysis is ongoing, the insects collected during this period appear to be gnat-like and possibly of the family Simuliidae or Sciaridae. The physical characteristics of the average insect from a particular flight are:

  • Mean mass (4 specimens) = 0.1 mg
  • Wing length (1 specimen) = 4.34 mm
  • Wing width, widest = 1.57 mm
  • Abdomen length (1 specimen) = 1.59 mm
  • Abdomen width (1 specimen) = 0.96 mm
  • Body length (1 specimen) = 2.01 mm

In a typical flight, approximately 70 insects were collected during one hour at several hundred meters altitude. This equates to roughly one insect per range gate most of the time.

Resolution of MMCR Calibration Uncertainty: Comparison of MMCR and CPRS reflectivity from the Fall 1997 IOP revealed an approximately 4 dbZ difference with the MMCR lower than the CPRS. While plans were to collect additional data for intercomparison purposes to identify the source of this offset, the source was identified before the IOP by Dr. Ken Moran of the NOAA Environmental Technology Laboratory. The offset occurred due to an incorrect treatment of the Hanning Window when performing FFT’s to generate Doppler Spectra.

Performance of the visiting instruments was mixed. The University of Utah PDL did not arrive until the beginning of the second week of the IOP due to mechanical failure of the PDL van. The University of Utah millimeter radar was not able to collect polarization data although the radar appeared to be quite sensitive and did collect many hours of radar reflectivity and Doppler moments during cirrus cloud events. The digital signal processing board used by PSU to collect MMCR voltages had a problem with ringing in the analog to digital circuitry that caused some ambiguity in the signal although careful data processing will largely correct this problem. The hemispheric sky imager and the CPRS performed well.

In Summary, all IOP objectives were met, although only a few cloud events were available for sampling. Preliminary examination of the data is quite encouraging and analysis of these data will be ongoing.

Additional Information

Important Phone Numbers Central Facility (Ground Operations) Phone: 580-388-4053 Fax: 580-388-4052 E-mail: teske@ops.sgp.arm.gov

Ponca City Airport Greenwood Aviation: Phone: 580-762-2580 Fax: 580-762-8070

Citation Phone: 580-765-4477 Data: 580-765-1406

Blackwell/Tonkawa Airport Secretary: 580-363-0981 Fax: 580-363-0982 Pilots: 580-363-0980 Scientists: 580-363-0996

IOP Chief Scientist/Weather Cell Phones Cloud IOP - Jay Mace: 630-767-8624 Weather - Mike Splitt: 630-624-6166

Campaign Data Sets

IOP Participant Data Source Name Final Data
Ben Balsley Kite/Balloon Order Data
Chuck Long HIS Order Data
C. Platt IR Rad Order Data
Michael Poellot Citation Order Data
Kenneth Sassen Lidar Order Data
Kenneth Sassen Radar Order Data
Stephen Sekelsky CPRS: U. Mass. 33/95 GHz Cloud Profiling Radar System Order Data