Surface Meteorological Station

This document describes the instruments and data format used in the NOAA Aeronomy Laboratory TRMM profiler system for surface meteorological data. For TEFLUN-A, only the rain gage was used. For the other three TRMM field campaigns other instruments were added to measure wind, temperature, relative humidity, pressure, and solar radiation.

The instruments are high quality instruments, but may not be mounted for optimal data. The information from these instruments is to be used as an indication of the local meteorological conditions.

Description of Instruments

Data Logger

The basic data logger is a Campbell Scientific CR-10. The data from each instrument was sampled every 0.5 second by the CR-10. Every 10 seconds, a 10 second average was transmitted by the CR-10 to a computer for display and archival. As part of the 10 second average, a time stamp was added to the data. The time stamp is the time of the creation of the average, making it the end of the sampling time. The clock in the CR-10 is kept in UT time, and is set weekly to the GPS time standard.

Wind Sensor
The wind sensor is a R. M. Young Wind Monitor. It is mounted on a pole about 6 feet above the top of the container.

Barometer
The barometer is a Vaisala PTA-427 unit. It is mounted inside the CR-10 data logger case, which is located inside the container. It is recorded as pressure-800 hPa to keep the precision of the data constant as the pressure varies around 1000 hPa.

Air Temperature and Relative Humidity Sensor
The air temperature and relative humidity sensor is a Vaisala HMP35C inside a 12-plate GILL Radiation Shield. It is mounted just above the top of the container, on the met instrument pole.

Solar Radiation Sensor
The solar radiation sensor is a LI-COR LI200S silicon pyranometer. It is placed on an arm just below the wind sensor, near the top of the met. instrument pole. It reads total sun and sky solar radiation, in the 400-1100 nm band.

Rain Bucket
The rain bucket is a tipping bucket rain gage, calibrated to output a tip every .01 inch. It is located on top of the container, near the center.

Meteorological Data Format
The meteorological data is stored in one text file for each day. The file name is CRyydddA.txt, where yy is the last two digits of the year, and ddd is the day of the year. These data files are recorded at the site, and have had no post-processing applied to them. Periods of missing data signify a power outage, or some other disruption of the computer software. A typical data file is about 1 megabyte in size. This data file format is used at most of our sites. The data is sampled every .5 seconds. For TRMM, the data is averaged for 10 seconds. NOTE: The time indicated in the file is the END of the Sample Period.

Table 1. Surface Meteorological Data File Format

column Description Units
1 Array ID
2 Year
3 Day of year
4 Hour and Minute in hhmm format, leading hour digits suppressed UT time
5 Seconds at END of sample period
6 Mean horizontal wind speed, S=sum(wind speed samples)/number of samples m/s
7 Resultant mean wind speed, U=Square root( Average East component squared + Average North component squared) m/s
8 Resultant mean wind direction, Ou=arctan(Average East component/Average North component) degrees
9 Standard deviation of wind direction, stdou=81*Square root(1-U/S) degrees
10 Mean horizontal wind speed, S=sum(wind speed samples)/number of samples, same as column 6 m/s
11 Unit vector mean wind direction, O1=Arctan(Ux/Uy), where Ux=sum(Ue/Ui)/number of samples, where Ui=Square Root(Ue^2+Un^2), and Uy=Ux=sum(Un/Ui)/number of samples. degrees
12 Standard deviation of wind direction, calculated using the Yamartino algorithm. This option complies with EPA guidelines for use with straight-line Gaussian dispersion models to model plume transport. degrees
13 Temperature degrees C
14 Relative Humidity %
15 Pressure - 800 hPa hPa
16 Incoming Solar radiation kW/m2
17 Total rain count in averaging interval mm
18 Battery Voltage V
19 Internal Temperature data logger container degrees C
Note. For TEFLUN-A, only the time, rain gage, battery voltage, and internal enclosure temperature fields are valid.

Sample Data
A sample data line from TEFLUN-B in Florida appears below. In the data files, this would be one line of the file. This data is for the averaging period that ended at 00:00:10.215 on day 234 of 1998. The wind speed was about .2 m/s from 87. The temperature was 27.9, and the relative humidity was 87%. The pressure was 1017 hPa. The solar radiation is negative, which signifies that it is dark. During this averaging period there was no rain recorded. The battery in the CR-10 data logger was at 13.2 V, and the data logger temperature was 27.3:

111,1998,234,0,10.125,.1872,.1872,86.946,.16066,.1872,86.937,.15506,27.925,86.758,217.46,-.01992,0,13.17,27.3

A second line from the same day is shown below. This data is for the averaging period that ended at 19:02:40.215 on day 234 of 1998. The wind speed was about 2.4 m/s from 50. The temperature was 27.3, and the relative humidity was 87%. The pressure was 1015 hPa. The solar radiation is 0.107 kWm-2. During this averaging period there was 0.254 mm rain recorded. The battery in the CR-10 data logger was at 13.2 V, and the data logger temperature was 27.7:

111,1998,234,1902,40.125,2.4216,2.356,50.158,13.335,2.4216,48.052,13.342,27.284,86.639,215.28,.10656,.254,13.16,27.69

Zipped ASCII Surface Meteorological Data Files

The daily ASCII surface meteorological data files have been "zipped" into one file: teflun_a_met.zip.

(Download free unzip software for Windows or Mac.)