FLATLAND96: Flatland Observatory Project II

Summary

The 1996 Flatland Atmospheric Boundary Layer Experiment, FLATLAND96, was an investigation of the structure and dynamics of the planetary boundary layer. The scientific objectives of the study were:

1. To measure entrainment velocity in the convective boundary layer

2. To measure the spatial and temporal variations of boundary layer height

3. To measure the thickness and time evolution of the entrainment zone

4. To measure the turbulent heat flux

5. To measure temperature advection term of the heat budget

6. To measure heat storage term of the heat budget

7. To measure or estimate the boundary layer-top heat flux and entrainment parameter.

8. To compare cloud-topped and cloud-free boundary layers

9. To measure surface flux differences between corn and soybean fields

In addition to the scientific objectives, FLATLAND96 also served to develop instrumentation and methodology. The associated instrumental and technique objectives were:

1. To characterize the accuracy and precision of boundary layer height measurements

2. To compare turbulent heat flux measurement techniques (similarity, eddy correlation, conditional sampling)

3. To compare direct vertical velocity measurements to those from divergence

4. To prepare for the 1997 soil flux study

5. To compare radar and lidar measurements of boundary layer structure and winds

6. To improve understanding of scattering mechanisms

These scientific and methodological objectives were to be achieved by using the following instruments and data sets:

1. Profilers. Three 915-MHz boundary layer radar wind profilers were deployed in a triangle. Two Integrated Sounding Systems from the NCAR facilities pool were deployed in addition to the existing FAO profiler.

2. Surface meteorology stations. The two ISSs and the FAO base had surface meteorological instruments measuring wind speed and direction (at 10 m), temperature, humidity, and rainfall.

3. Flux-PAM. Three Flux-PAM systems from the NCAR facilities pool were deployed to measure surface fluxes. One Flux-PAM augmented with components of the ASTER facility was equipped with a fast-response ozone sensor for measuring surface ozone flux during the latter part of the campaign.

4. Rawinsondes. Rawinsondes were flown from one of the two ISSs as described below.

5. Ceilometer. A Vaisala CT-25K laser ceilometer was deployed at FAO to provide cloud base and backscatter profile information. This became a permanent instrument at FAO.

6. Lidars. Three lidars from NCAR and NOAA were deployed at the Monticello Road site 26 July - 15 August in a separate project known as LIFT.

The profiler triangle sites were chosen based on a number of factors, including the precision of divergence measurements, scale of processes to be measured, horizontal homogeneity, ability to compare results from three instruments, ability to use RASS (full-time if possible), and logistics. The triangle is the same as used in the Flatland95 campaign, with legs approximately 5.5, 7.5, and 8 km.