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 100-200m).

• High-moisture regions are 600-800m 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

PayloadMass

(kg)

WingLoading

(oz/ft)

RequiredAirspeed

(m/s)

SamplingResolution

(m)

0 15.5 8.5 8.5

1 19.0 9.4 9.4

2 22.86 10.3 10.3

3 26.67 11.2 11.2

4 30.48 12.1 12.1

Observation Point Source Region• Function of the ambient wind speed

tVVxx wa *)(0

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.