TA-6 Station Description

TA-6

Alternate Name(s): None

Measurements:
The TA-6 station consists of a 92-meter tower instrumented for wind and temperature at four levels and near-surface instrumentation for measuring temperature, moisture, pressure, precipitation, and surface energy balance terms. The SODAR is also located at this site. A SODAR (sonic detection and ranging) is an acoustic system used to remotely measure wind and turbulence characteristics in the lower atmosphere. In operation, the antenna emits short sound pulses which are backscattered by temperature inhomogeneites in the air. The SODAR then evaluates amplitude and frequency changes in the backscattered sound waves, from which it calculates detailed information about the turbulence and wind structure of the lower atmosphere.  See Table 13.4 in the Meteorological Monitoring Plan for measurement details and Table 13.3 in the same document for definitions of variables.

Data Type Record Begins Record Ends
15-min dataFebruary 1, 1990

(still active)
24-h data February 1, 1990

(still active)

TA-6 has been the official meteorological station for Los Alamos since August 1990. Climate statistics for the upper Pajarito Plateau are compiled from observations from this station. Temperature and precipitation observations from this station are reported to the National Weather Service (NWS) Cooperative Observer Network and are archived at the National Climatic Data Center.

Site Description:
The TA-6 tower and associated near-surface instrumentation are located on the Pajarito Plateau in an east-west meadow on Two-mile Mesa. The view of the station, as shown in the above photograph, is looking west-northwest toward the Jemez Mountains.  Vegetation covers about 80% of the surface.  Ponderosa pines of 12-m height grew within 100 m of the tower to the south and within 150 m to the north, but the Cerro Grande fire destroyed much of the forest in the area.  The fetch within a few hundred meters of the tower is over short grasses and widely scattered low shrubs.  The roughness length, based on turbulence, varies from 0.4 m to 0.8 m depending on wind direction. Soil type is classified as Carjo loam and the plateau tilts at about 1.5 degrees to the east-southeast.

Location and Elevation:
Coordinate System x y
NAD 27 State Plane Coordinates (ft) 479551 1768778
UTM, Zone 13 (m) 380856.80 3969385.15
Longitude & Latitude (d, m, s)-106° 19' 8.4" 35° 51' 41.1"

Station elevation is 7424 ft (2263.4 m) above sea level.

The tower is LANL structure no. TA-06-0078; the datalogger shed is LANL structure no. TA-06-0091; and the sodar is LANL structure no. TA-06-0100.

Data Quality:

General Remarks
There were several problems bringing this station on line in the February 1990 through June 1990 period. Depending on the type of data requested, you may find missing data during this period. For the most part, all suspect data have been replaced with an asterisk (*). Occasionally you will see days on which all the 15-min data appear good, but some of the 24-h summary values are missing. Lightning strikes, momentary power outages, or the need to reload the datalogger program may be the cause. In these cases, you can estimate a 24-h value from the 15-min data.

See Section C.1.b and c of the Meteorological Monitoring Plan for details on sampling and general remarks concerning accuracy.

Qualifying remarks are organized by data type (for example, wind, atmospheric state, etc.), and we use our standard variable names, as defined in Table 13.3 of the Meteorological Monitoring Plan.

Wind Variables
Wind direction measurements (dir) from sometime in January 1990 through April 19, 1990, were affected by an inappropriate resistor in the circuit. Because of the averaging done in the datalogger, there is no accurate way of reconstructing these data. If you need wind direction data during the period of time, contact a meteorologist.

The measurement of the vertical velocity (w) has been multiplied by 1.25 to correct for the non-cosine response of the propeller. All quantities derived from the w signal, therefore, include this correction. The w signal is occasionally affected by wet snow and ice. Although we have attempted to edit the data when this happens, you will occasionally see periods of several hours when w and its standard deviation (sdw) go to zero during the winter; a frozen propeller is the cause.

Most of the instantaneous wind gust directions (dirgst) are erroneous prior to February 24 1999 at 15:15 MST. However, directions for the 1-min wind gusts (dir1gst) are correct.

Atmospheric State Variables
From November 09, 1991, to April 30,1992, datalogger connections for temperature at the upper two levels (temp3 and temp4) were reversed. If you are interested in temperature profiles during this period of time, contact a meteorologist.

Occasionally one encounters relative humidity (rh) values exceeding 100%; we recommend changing these values to 100%. Because rh is used in the calculation of the dew point temperature (dewp), there may be instances when dewp > temp.

Precipitation-related Variables
No known problems.

Radiative Energy Variables
During snow or frost formation (and for some time after), the domes of the upward looking pyranometers and pyrgeometers may become snow or ice covered. In such instances the shortwave irradiance (swdn) is diminished, and the long-wave atmospheric irradiance (lwdn) is greater than it should be. Our editing has not been consistent: In portions of the record we attempted to remove these snow and frost effects and in other portions we decided not to edit. In general, it is difficult to decide when the melting is complete and the signal is back to normal. Because swdn and lwdn are used in the calculation of the net radiation (netrad), netrad is also affected.

As a result of a change in the calibration standard used by the manufacturer, measurements of swdn and swup are 5% too large from the beginning of the record to 1030 MST on February 22, 1995.

During the daytime, lwdn may be over-estimated by an amount equal to 2.7% of swdn because of heating of the dome (see A. D. Culf and J. H. C. Gash, "Longwave Radiation from Clear Skies in Niger: a Comparison of Observations with Simple Formulas," J. Appl. Meteor., 32, 539-547, 1993).

Prior to February 8, 1991, lwdn was estimated by subtracting swdn from a measurement of the all-wave radiation. Because the all-wave radiation measurement was made with a low-quality pyrradiometer, estimates of lwdn during that period are unreliable; the measurement of netrad is also suspect during this period. After February 8, 1991, lwdn was measured directly with a good quality pyrgeometer.

Eddy Heat Flux Variables
The measurements of the latent heat (lheati) and sensible heat (sheat) fluxes are based on the eddy correlation method; see Section C.1.b and c of the Meteorological Monitoring Plan for a discussion of high-frequency loss.

We do not recommend using lheat data archived before September 3, 1992; we had problems with the fast-response hygrometer before that date. Occasionally you will see small negative values of lheat; these are probably meaningless.

Since lheat is used in the algorithm for calculating sheat, we caution against using sheat data before September 3, 1992; however, the resulting errors in sheat are expected to be negligible most of the time.

Sub-surface Variables
The following potential problems should be noted when using the ground heat flux data (gheat): (1) We do not adjust the sensor's calibration factor to account for differences between soil and sensor conductivities. (3) Occasionally heavy rain washes away the 1-2 mm of soil that usually covers the sensor, exposing it to the sun. (2) Because it is a point measurement, it may not be very representative of the site.