Part II: Turbulence Signature and Platform Limitations Dan Weber, Frank W. Gallagher, Ken Howard ©2000 Frank W. Gallagher III

Another Look at the Data and the Platform Capabilities How much of the boundary layer turbulence can be captured? Can we use the data in a numerical model (3-D usefulness)? What are the system limitations?

Outline Generate a 3-D picture Discuss turbulence features Investigate the current limitations of the platform: –Resolution –Sampling space Summary and future efforts

Flight Path for June 29, 2000

ADAS Analysis Generate a 3-D data set via ADAS analysis from point measurements. Use MCDRS (aircraft option) to bring in the observations. High-resolution (20m) grid. Barnes analysis –4 passes –Horizontal range influence 90,80,70,60m –Vertical range influence 60,50,40,30m

ADAS Analysis Continued Background field, Norman OK 12Z sounding, 3-D and horizontally homogeneous Data collected from 15:07 to 15:33Z Analyzed variables: –Temperature –Pressure –Mixing ratio

ADAS Results North-South Slice X-Y Slice at 800m Mixing Ratio

ADAS Analysis Discussion Analysis shows small convective elements (order m). High-moisture regions are m removed from the source region (surface). Complex structure exists. More data is needed to “fill in our volume”.

Turbulence Indicators Classical indicators (given the current data set) include: –Mean –Variance –Vertical flux Others not possible: –Covariance (requires vertical velocity)

Turbulence Results Horizontally Averaged Mean (analysis points with data only) Variance Potential Temperature Mixing Ratio

Turbulence Results Potential Temperature Mixing Ratio Normalized Vertical Flux

Turbulence Summary Horizontally averaged means and variances follow convective boundary layer theory. Vertical moisture flux vary widely but the trend follows the expected result for a heated boundary layer. Entrainment is strong at the top of the mixed layer. A larger data set is needed to increase the averaging space and produce a clearer turbulence picture.

Platform Limitation Analysis Need to address the following: –Observation resolution is a function of: Instrument sampling rate Aircraft flight characteristics Flight path analysis –Reference frame/source region Can we use the data to initialize a numerical model?

Resolution Issues Function of airspeed and sampling rate –Instrument sampling rate: 1 hertz –Aircraft airspeed: function of wind loading sampling resolution = airspeed/sampling rate

Observation Point Source Region Function of the ambient wind speed Earth Frame Atmosphere (source) Wind

Model Initialization Need a coherent volume of data. Strongly coupled features. More data is needed than collected in the June Field study. Platform resolution is sufficient for LES studies.

Summary Sampling resolution on the order of 10m is sufficient for observing boundary layer structures and turbulence. Difficulty remains in regards to the source region. A moderate to strong mean wind will hinder detailed studies as the source region continues to vary w.r.t the earth and a numerical model domain. ***Age old sampling problem***

Future Efforts Pre-storm environment and severe weather observations, dust devils and more turbulence studies. New platform may be required to expand capabilities into high-wind environments. Redundant sensors using smaller components. Expand the sensor array to include wind speeds and insert data into a numerical model.