AHATS

Overview

AHATS was a boundary turbulence study in the San Joaquin Valley, California, during the summer of 2008.   The PIs on the project were Chenning Tong (Clemson), John Wyngaard (Penn State), Tom Horst (NCAR) and Peter Sullivan (NCAR).  The NCAR facilities involved were the ISFS and the ISS.   Data from these facilities can be accessed here.

AHATS was the fourth in the series of Horizontal Array of Turbulence Studies (HATS).  This series of experiments aims to improve large-eddy simulations (LES) of turbulence close to the Earth's surface, by collecting data that can be spatially filtered into scales that can be simulated by LES and those that must be parametrized. 

These experiments were:

The first 3 experiments all used two horizontal lines of 9 sonic anemometers to provide cross-stream filtered velocity and temperature statistics.

AHATS returned to the original HATS site, but a third line was added upwind to provide spatial differences in the streamwise direction.  In addition, two horizontal lines of turbulent pressure sensors were added to AHATS to investigate, for the first time, resolved and parameterized pressure correlation terms in the turbulence transport equations. Those capabilities were unavailable in previous field programs but are important for understanding the SGS turbulence and for testing SGS models that are based on the SGS physics.

Chronology

Logbook

The AHATS logbook provides detailed information about the operation of the experiment.  This page has other information as well.

Photographs (links to old Confluence site -- will be migrated here eventually...)

• Setup
• Wide Array
• Medium Array
• Medium-staggered Array
• Narrow Array

Sensor Data Post-Processing

Sonic Anemometer

Data editing

The AHATS sonic data have been edited to remove obviously bad data, putting NA's in the cal_files when the 5-minute averages of the sonic diagnostic variable exceeded ~0.5.  During the first configuration, these usually occurred simultaneously on all channels of one of the four sonic adams, suggesting that the adam could not keep up with data ingest when there were transmission problems back to the base.  After the first configuration, simultaneous problems on all channels of an adam occurred less frequently and with smaller 'diag' values.  Then most of the high 'diag' values were associated with the beginning or end of a period of lost data.

 For configuration 4, after August 8, sonic 6u had recurring continuous periods in the middle of the day with 'diag' values between 0.05 and 0.1.  I did not edity these out because it would have removed a significant fraction of the data from 6u during configuration 4.

Sonic zero-wind offsets

Prior to the field project, all sonics were checked for zero-wind offsets at room temperature.  Those with offsets larger than 4-5 cm/s were returned to the manufacturer for recalibration.  Following the project, we repeated this test and found that 26 out of 41 sonics had offsets exceeding 4-6 cm/s.  A few had offsets up to 20-30 cm/s.  We do not know when or at what rate these changes occurred.

Subsequently, we have run each of the sonics used in AHATS in a zero-wind chamber inside a temperature-controlled chamber in the NCAR Sensor Calibration Laboratory to determine the offsets for each wind component.  This is similar to one aspect of the manufacturer's recalibration process wherein offsets are determined as a function of temperature and entered into the sonic firmware for correction of the measured wind data. The chamber temperature was ramped from 60 C down to -30 C over a 6-hour time period (black lines), then back up to 60 C over a second 6-hour time period (red lines), and finally allowed to cool down with the temperature control turned off (green lines).   Data collection was terminated at somewhat arbitrary times during the last cool-down phase.

The following table lists the sonics by serial number (and location) and includes links to plots of NCAR post-project measurements of the wind offsets as a function of temperature.  The table also lists the maximum offset (cm/s) for each orthogonal wind component and the temperature at which the maximum occurs.

*cycle-slip errors cause jumps in temperature and wind offsets, generally at low temperatures

**data from Campbell recalibration

***Location notation: u = upwind (numbered from NE to SW); b = downwind, bottom; t = downwind, top; ht(m) = profile tower

Data Access

• ISFS 5 minute average statistics in NetCDF format
• ISFS 5 minute average statistics in ASCII format (via Java Applet -- NOT YET WORKABLE)
• ISFS High-rate time series data available on request
• ISS (Integrated Sounding System) Data Page for AHATS

Links

• Site survey notes
• Pre-experiment flow distortion testing