SGP/TWR/C1 - West-side 25m Temp/RH Calibration

On Feb 7 a communication problem was discovered for the 25 m level system. In 
troubleshooting the system, the power to the dataloggers was turned off. This caused the programs 
from the storage modules to automatically load into the datalogger.  These programs 
contained the wrong calibration for the T/RH sensors.  

Only the 25m temperature calibrations were significantly affected. The error in the 60m 
temperature data is only +0.2 degrees C at maximum.

• Standard Deviation of Relative Humidity(sd_rh)
• Standard Deviation of Air Temperature(sd_temp)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Vapor Pressure (kiloPascals)(vap_pres)
• Beam 0 Temperature(temp)

• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)

• Minimum Temperature(min_temp)
• Maximum Temperature(max_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - West-side 25m RH replacement

I have reviewed the T/RH data from the 25 and 60 meter levels and find that all sensors 
were working, but that the 25m RH did not compare favorably with the 60m RH, SMOS RH, EBBR 
RH, or BBSS RH data.  An error in the sensitivity of the 25m RH can be seen for RHs less 
than 90%.  Above 90% there is good agreement with the other systems.

A comparison of data (25m and 60m tower, SMOS, and BBSS) for two weeks showed that 25m RH 
was typically about 5% to 9% too high, and thus calculated vapor pressures were about 
0.05 to 0.09 kPa too high.

Temperatures from the 25m and 60m levels continue to be consistent with expected 
temperature gradients and with the BBSS data.  When the temperature was rising, the 60 meter 
temperature was usually lower than the 25 meter temperature.  When temperature was dropping, 
the 60 meter temperature was usually higher than the 25 meter temperature.  That is the 
expected pattern.

On March 19, 1996, the 25m RH probe was replaced.

• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)

• Relative humidity inside the instrument enclosure(rh)

• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)

SGP/TWR/C1 - 25m RH replacement

Site Operations replaced the 25m RH probe on 19 March 1996 from 1905 to 2130 GMT.

I have reviewed the T/RH data from the 25 meter level and find that the RH sensor was 
working, but that the 25m RH did not compare favorably with the 60m RH, or EBBR RH data.  An 
error in the sensitivity of the 25m RH can be seen for 
the whole range of RH.

A comparison of data from the affected period showed that 25m RH was typically about 8% 
too low at 50% RH and 15% too low at 24%, and thus calculated vapor pressures were about 
0.02 to 0.05 kPa too low, respectively.

Temperatures from the 25m and 60m levels continue to be consistent with expected 
temperature gradients and with the BBSS data. 

On March 25, 1996, the 25m RH probe was replaced again.

• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)

• Relative humidity inside the instrument enclosure(rh)

• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)

SGP/TWR/C1 - 25m Problems with RH probe

Site Operations replaced the 25m RH probe on 25 March 1996.

I have reviewed the T/RH data from the 25 meter level and find that the RH sensor was 
working, but that the 25m RH did not compare favorably with the 60m RH, or EBBR RH data.  An 
error in the sensitivity of the 25m RH can be seen for 
the whole range of RH.

A comparison of data showed that 25m RH was 19% too low for RH < 80%, 18% too low for RH 
between 80% and 85%, and 17% too low for RH > 85%.  Thus calculated vapor pressures were 
also too low.  With this information, adjustments can be made (by the user) in the data 
from March 25 through 2 April.

On April 2 and 3, 1996, I was assisted by Chris Martin in testing the 25m RH probe.  We 
lowered the 25 and 60 meter tower carriages to the surface.  The RH data from 2 April at 
1607 to 2240 GMT for both 25 and 60m levels was taken at about 2 to 3 meters above the 
surface.  Furthermore, much of the T/RH/Aspirator data is corrupted because of tests; data 
from this period is incorrect.

A multiplier of 1.04 was applied to the 25 meter RH data for the period 2 April at 2240 
GMT to 3 April at 1700 GMT; therefore, for this short period, a different adjustment by the 
data user is needed (multiply 25m RH by 1.144 for RH < 80%, by 1.135 for RH between 80% 
and 85%, and by 1.125 for RH > 85%).

On April 3, 1996 at 1700 GMT I increased the 25m RH multiplier to 1.19. Thereafter, the 
25m RH values must be decreased by 1% for RH between 80% and 85%, and decreased 2% for RH > 
85%.  The slight non-linearity of this type of RH probe at greater than 80% RH is 
exaggerated for this probe by it not being properly electronically calibrated.  Using the 
information above, the RH values above 80% can be adjusted to within 1% of the accuracy that 
would be obtained from a factory calibration.

• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)

• Relative humidity inside the instrument enclosure(rh)

• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)

SGP/TWR/C1 - Missing data

Data are missing and unrecoverable.

• Time offset of tweaks from base_time(time_offset)
• lon(lon)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Vapor Pressure (kiloPascals)(vap_pres)
• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Beam 0 Temperature(temp)
• lat(lat)
• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)
• base time(base_time)
• Dummy altitude for Zeb(alt)

• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Batter Voltage(vbat)
• Dummy altitude for Zeb(alt)
• Time offset of tweaks from base_time(time_offset)
• lon(lon)
• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• lat(lat)
• base time(base_time)

• lon(lon)
• Time of Maximum Relative Humidity(time_max_rh)
• lat(lat)
• Time of Maximum Vapor Pressure(time_max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Time offset of tweaks from base_time(time_offset)
• Minimum Temperature(min_temp)
• Time of Minimum Relative Humidity(time_min_rh)
• Time of Minimum Temperature(time_min_temp)
• Maximum Temperature(max_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Dummy altitude for Zeb(alt)
• Time of Maximum Temperature(time_max_temp)
• base time(base_time)
• Time of Minimum Vapor Pressure(time_min_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR25m/C1 - Reprocess: Global Metadata Error

The sensor_height global attribute field of the 25 meter data (1 minute, 30 minute, daily) 
lists the height as "60m" instead of "25m".

No data values are impacted by this error.

• base time(base_time)

• base time(base_time)

• base time(base_time)

SGP/TWR/C1 - 25m and 60m T/RH Calibration

The T and RH measurements at the 60 m tower level may need to be adjusted 
for times between the period listed above; this is concluded from 
calibrations/checks of the T/RH data during 21-24 May 1996.   On May 21-23, 
the 25 and 60 meter level west carriages were located at the surface for 
installation of the ECOR C1 system and calibrations/checks of the T/RH sensors.
ECOR installation took place primarily on 21 May.  

A table at the bottom of this text gives recommendations concerning use of the 
data from the period above, based on the data during the period and the 
condition of the T/RH sensors as found on 22-23 May 1996.

I planned recalibration/checks of the 25 m and 60 m level T/RH sensors in 
conjunction with a trip to the Central Facility to observe ECOR 
C1 installation and training.  

The 60 m T data began to show signs of deterioration of accuracy after 20 April
1996.  This became most noticeable by 25 April as the occurrence of 
transitional periods (as determined from comparison of the 25 and 60 m T) 
became marginal.  The 60 m temperature appeared to be too low most of the 
time.
  
At the same time, the 60 m RH appeared to be too high.  It is difficult to 
determine what the actual difference between sensors is when the carriages are 
at the 25 and 60 m levels, especially if one temperature sensor is reporting 
incorrectly.  The RH sensor measurements can be compared fairly easily during 
the day to night transition period (as determined from the temperatures at the
two levels) as a difference in temperature of about 0.7 degrees corresponds to
an RH difference of about 5%; smaller differences in each are proportional;
when the temperatures are within about 0.1 degree, the RH should be within 
about 1%.  Careful study of the data during the transition time (which varies 
as to time of day during the year) allows me to determine the quality of the 
measurements.  The ECOR C1 installation provided the perfect opportunity to 
compare the T/RH sensors for a long period of time when the data would have 
been incorrect anyway.  

With the carriages and sensors at the tower base, the RH and temperature 
sensors were compared on 22 May.  The 60 m RH probe indicated an average 
of 62% while the 25 m RH probe and an aspirated psychrometer indicated 51%. 
The multiplier in the 60 m CR21X program (1.14) accounted for all but 4% of 
the difference.  An interesting, but confusing, sidenote to this is that 
the multiplier that I entered on 3 April 1996 was 1.19; I did not have time 
before I left the CF to change the factor in the storage module from 1.14 
to 1.19.  I submitted a work request to site operations to have the program 
with 1.19 multiplier downloaded manually from the CR21X to the storage module
(a precaution in case power to the logger was lost and the logger would 
have to restart from the storage module).  However, the program download 
apparently did not work, as at some later time (or perhaps at the time of 
the download attempt) the program with the 1.14 factor in the storage 
module was uploaded to the CR21X. 

No power outages are known to have occurred thereafter that would have caused 
uploading of the storage module program to the datalogger (which would have 
resulted in the 1.14 multiplier ending up in the CR21X), except on 21 May 
1996 from 2027 to 2127 GMT.  At this time, Site Operations had to disconnect
the AC charger unit for the CR21X machines to permit the installation of other
devices related to the ECOR C1 installation.  However, the CR21X battery 
voltage did not drop low enough for ceasation of the on-board program.  
Since RH frequently decreases more than 5% between half hour values and 
sometimes does so between one minute values, it is impossible to tell when 
the multiplier changed from 1.19 to 1.14.

If it appears to the data user that the 25 m RH is low, it could be 
multiplied by 1.19/1.14=1.044.  It may be more appropriate to use the 
smaller multiplier, since the RH sensor output was drifting upwards anyway.
By the end of the period above, the 60 meter RH should be be decreased by a 
factor of 1.2.

Even though the actual difference between the 25 and 60 m RH probes (with a 
multiplier of 1.0 for both), at the tower base, was only about 4% (within 
their combined specifications), we removed 60 m RH probe S/N 109 and replaced 
it with RH probe S/N 234 at 1940 GMT on 22 May.  S/N 234 indicated, on 
average, 55% while the 25 m RH probe and the aspirated psychrometer indicated 
51%.  These were the same results obtained with the previous RH sensor.  
Instead of switching back to the original RH sensor, S/N 234 was left on.

The instruments were left at the tower base overnight to compare the T and 
RH from the two levels.  Over a range of RH of 50% to 81% the ratio of 25 m 
to 60 m RH was incredibly consistent at 0.911.  Therefore, on 23 May at 
2000 GMT, a multiplier of 0.911 was entered in the CR21X program for the 60 m 
RH.  This was justified by comparisons with the psychrometer that indicated 
that the 25 m RH sensor agreed with the psychrometer.

The overnight comparison also showed what manual measurements on May 22 
had, that the 60 m temperature sensor was indicating low.  An
ice bath test of the 25 and 60 m PRTds showed that both were within 0.1 
degrees of zero.  At ambient T (30 deg. C), the 25 m sensor and the 
psychrometer agreed, but the 60 m PRTD indicated 1.5 degrees low.  Changes 
in calibration slope of PRTD sensors are not common, but are possible if 
the actual sensing element is moved inside the stainless steel jacket.  
Since most of the change in calibration appears to have happened within a 
week in late April, it is possible that tower vibration may have been the 
cause.  Again, it is not possible to easily quantify how the 60 m T data 
should be adjusted from 3 April until 21 May.  For several consecutive half
hours on 22 May, while both levels of sensors were at the tower base, the 
60 m T actually indicated a greater temperature than the 25 m level T 
sensor (and the 60 m RH was lower than the 25 m level).  Such erratic behavior
precludes being able to make any recommendation for adjustment of the 60 m T 
beyond 20 April (or for the 60 m RH beyond 8 May).

The 60 m temperature sensor was replaced at 1559 GMT on 23 May.  An ice bath 
was used to determine the proper Rs/Ro and an ambient comparison between the 
25 m and 60 m PRTDs and the psychrometer was performed.  All agreed within
0.15 degrees over a couple of hours.  The tower carriages were then 
elevated to their normal positions at 25 and 60 meters.  The next morning 
the data from the two levels and the SMOS were compared and found to 
produce reasonable gradients and mean values.  A review of the data since 
that time continues to show that the data quality is excellent.  

Side by side comparison of the two sets of sensors over an extended period of 
time (overnight) allows the best evaluation of performance; this technique will 
continue to be used in the future in the interest of ensuring data quality.

One footnote to the T/RH checks/calibrations is that the aspirator
threshhold level was reset to 2200 mv for both 25 m and 60 m aspirators.  
This appears to be the optimum threshhold for both levels at this time; the 
threshhold cannot be an unchangeable value, as it varies dependent on length of 
cable on the tower and age and condition of the flow sensor and aspirator 
fan.  I have to continually evaluate the effectiveness of the threshhold 
and adjust it when appropriate, a result of the sensor being a variable 
output device, as opposed to the on/off switch type that is used by some 
manufacturers.

Table of 60 m Data Usage

Temperature:

3  Apr - 20 Apr   no adjustments
20 Apr - 21 May   no recommendation

Relative Humidity:

3 Apr -  8 May   no adjustments
8 May - 21 May   no recommendation

• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Vapor Pressure (kiloPascals)(vap_pres)
• Beam 0 Temperature(temp)
• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)

• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)

• Maximum Relative Humidity(max_rh)
• Maximum Temperature(max_temp)
• Minimum Temperature(min_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)
• Minimum Relative Humidity(min_rh)

• Beam 0 Temperature(temp)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Temperature(min_temp)
• Maximum Temperature(max_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - Reprocess: RH recalibration

Comparisons of the RH probes with Oklahoma Mesonet probes in the laboratory and 
comparisons of the RH probes with the EBBR over a four day period after the Water Vapor IOP 
indicate the TOWER RH probes were incorrectly  calibrated. Corrections required are summarized 
below.

60 meter level: 
RH data greater than 85% are incorrect for 23 May 1996 through 10 September 2000 GMT.

RH data for 10 September 2330 GMT through 13 September 2130 GMT can be corrected with the 
following equation:
  -1.6 + 0.955*RH 
for original RH of 83% or less. Original RH values of greater than 83% cannot be 
adequately corrected.

RH data for 14 September 0000 GMT through 30 September 2000 GMT can be corrected with the 
equation:
  -1.6 + 0.87*RH
for original RH of 83% or less. Original RH values of greater than 83% cannot be 
adequately corrected. 

RH data for 30 September 2030 GMT through 21 October 1830 GMT can be corrected with the 
equation: 
  0.3 + 1.107*RH
for original RH of 85% or less.  Original RH values of greater than 85% cannot be 
adequately corrected. 


25 meter level:
RH data greater than 90% are incorrect for 23 May 1996 through 10 September 2000 GMT.

RH data for 10 September 0000 GMT through 21 October 1830 GMT can be corrected with the 
equation:
  4.098 + 0.953*RH 
for original RH of 90% or less.  Original RH values of greater than 90% cannot be 
adequately corrected. 

Vapor pressure is also incorrect because RH was incorrect.  Recalculate vapor pressure 
from the recalibrated RH.

• Standard Deviation of Relative Humidity(sd_rh)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Maximum Relative Humidity(max_rh)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)
• Minimum Relative Humidity(min_rh)

• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Maximum Vapor Pressure(max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - RH Probe affected by tower damage

On Feb. 3 and 4 the SGP CART 60 m tower western elevator was repaired.
This included the replacement of cables on the 60 m carriage and connectors on
the 25 m carriage.  Although damaged, the 60 m carriage cable had been 
temporarily repaired by Site Operations several months ago, with apparent 
success.  However, evidence since then suggests that the repair was not 
totally successful.  Tests since then suggest that the low return for the 
RH sensor may have been floating, or at least the connection was poor.  At 
the same time, the 25 m carriage connectors and tower receptacles were bent
in planes perpendicular to each other, apparently resulting in the same 
condition as existed for the 60 m carriage.  The damage was partially the
result of improper routing of the cables on the 60 m carriage by the tower 
installer and partially the result of improper parking of the carriages 
(damaging the 25 m carriage connectors and receptacles).  The cables were 
reoriented and the connectors and receptacles replaced by the tower 
installer on 3-4 Feb 97.

Because of the damage to the 25 m carriage connectors, the 25 m carriage 
was left off of the tower and no correct data was collected from the 25 m 
level from 22 Oct 97 at 1730 GMT until 4 Feb 97 at 1400 GMT.  Only the 60 m 
level reported useful data during this period.  During this period a slope 
of 1.107 was applied in the datalogger programming before the 60 m RH value
was output to the logger memory.  Calibrations of the probe by Vaisala last 
month show that the logger slope was appropriate for the sensor behavior at RH 
less than 85%.  Calibration of sensors SN 109 and 231 by Vaisala showed the 
outputs to be several percent low near 0% RH and nearly correct at 100%.  The 
calibrations by the original manufacturer caused the outputs to be outside 
the specifications for the bottom 3/4 of the sensors' range.  Vaisala 
adjusted the slope and offset for both sensors.

In use at 60 m on the tower, the RH probe slope changed above 85% RH, becoming
larger with increasing RH.  At saturation the 60 m sensor RH value was being 
reported as 110.7% to 111.0% (in other words the slope in the logger of 
1.107 X 100%).  Apparently, at higher voltages the poor low side connection 
was less of a factor in the voltage output by the probe.  Comparison with 
sonde data for RH above 85% yields the correction in the next paragraph.

Therefore, my recommendation for the period listed above is to use the 60 m 
RH data as is for RH less than 85%.  Reported RH above 85% can be roughly 
corrected with the following: actual RH = 36 + 0.577 X (60 m reported RH) . 

Vapor pressure can then be recalculated by the user from the correct RH 
values and the temperature.

On Feb. 4 and 5, I conducted a number of tests on the carriages and RH 
probes (SN 231 at 25 m, SN 109 at 60 m), then replaced the RH probes with 
the probes recently (SN 234 at 25 m, SN 226 at 60 m) calibrated by Vaisala.  

One minute 60 m T and RH data is extremely consistent with the data 
from the sonde at 60 m height since 5 Feb 1997.  In fact, the 
comparisons have never been better, reflecting the problem with obtaining 
correct calibrations from the original manufacturer (even before the tower 
was damaged), and the problems created by the damage on the tower.

The problems resulting from damage to the tower carriage cables and 
connectors began around June 1995 (although the 60 m AC cable and 25 m 
receptacles had been damaged at least twice previously).  I made a number of
corrections to the RH data between June 1995 and when the tower was 
repaired this past February. 

25 and 60 m T and RH data since the tower repairs and the Feb. 5, 1997 
replacement of the RH probes are very consistent with the sonde data.  The 
only significant difference between the 60 m RH probe and the sonde RH probe 
occurs when the surface to 60 m RH gradient is large; this is expected since 
the RH probe on the sonde cannot respond to large changes in gradient quickly 
enough to produce the same measurement as the 60 m tower RH probe.

I will continue to compare the sonde, SMOS, and tower sensors for data quality 
purposes, as I have routinely for the past year.

• Standard Deviation of Relative Humidity(sd_rh)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Maximum Relative Humidity(max_rh)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)
• Minimum Relative Humidity(min_rh)

• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Maximum Vapor Pressure(max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - Reprocess: 25m and 60m T/RH Comm Lines Switched

On 3 March 1997 an activity of unknown nature took place at SGP, causing 
the communication lines to the 25 and 60 meter T/RH to be switched.  The 
data indicates that the switch occurred between 1630 and 1700 GMT.  I 
submitted a work request to site operations to determine if the two levels 
were switched; they found that they were, as I suspected.  It is not clear 
where this occurred, although we do know that it did not happen at the 
tower CR21X dataloggers location.  The communication lines were temporarily 
"switched back" at the logger location on May 28 at 2110 GMT until it can be 
determined where the switch was actually made.

• Standard Deviation of Relative Humidity(sd_rh)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)

• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Standard Deviation of Air Temperature(sd_temp)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)

SGP/TWR/C1 - 25m Low battery voltage affected data

Shortly after 2003 GMT on 2 September 1997 a GFCI circuit breaker tripped in the tower 
base AC box, resulting in a drop in CR21X voltage of 0.4 volts in seven minutes.  This 
resulted in a steady drop in battery voltage for the next 30 hours, and incorrect, out of 
range, or missing values for temp, rh, and vap_pres.

• lat(lat)
• Time offset of tweaks from base_time(time_offset)
• lon(lon)
• Standard Deviation of Relative Humidity(sd_rh)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)
• base time(base_time)
• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Beam 0 Temperature(temp)
• Dummy altitude for Zeb(alt)

• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Batter Voltage(vbat)
• Dummy altitude for Zeb(alt)
• Time offset of tweaks from base_time(time_offset)
• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• lat(lat)
• base time(base_time)
• lon(lon)
• Beam 0 Temperature(temp)

SGP/TWR/C1 - Incorrect temperature coefficient

When the power was restored to the TWR25m following a battery failure, the program 
downloaded to the logger had an old coefficient in it for temperature (1.0043; should be 
1.0041).  The difference in temperature reported was less than 0.05 degrees; this data does not 
need to be corrected. Site Operations corrected the coefficient on 25 September 1997.

• Standard Deviation of Air Temperature(sd_temp)
• Beam 0 Temperature(temp)

• Beam 0 Temperature(temp)

SGP/TWR/C1 - Tower lowered for maintenance

The west-side tower elevators were lowered for maintenance and/or data are offscale during 
routine maintenance.

• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Vapor Pressure (kiloPascals)(vap_pres)
• Beam 0 Temperature(temp)
• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)

• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)

• Maximum Relative Humidity(max_rh)
• Maximum Temperature(max_temp)
• Time of Minimum Relative Humidity(time_min_rh)
• Time of Maximum Temperature(time_max_temp)
• Minimum Temperature(min_temp)
• Time of Maximum Relative Humidity(time_max_rh)
• Maximum Vapor Pressure(max_vap_pres)
• Time of Maximum Vapor Pressure(time_max_vap_pres)
• Time of Minimum Temperature(time_min_temp)
• Time of Minimum Vapor Pressure(time_min_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)
• Minimum Relative Humidity(min_rh)

• Beam 0 Temperature(temp)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Time of Maximum Relative Humidity(time_max_rh)
• Time of Maximum Vapor Pressure(time_max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Temperature(min_temp)
• Time of Minimum Relative Humidity(time_min_rh)
• Time of Minimum Temperature(time_min_temp)
• Maximum Temperature(max_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Time of Maximum Temperature(time_max_temp)
• Time of Minimum Vapor Pressure(time_min_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - Westside 25m RH Probe Replacement

The 25 meter west RH part of the T/RH probe died suddenly on 5 January at about 2247 GMT.  
All RH and vapor pressure from that probe are incorrect until 13 February at 2015 GMT, 
after replacement of the probe.

• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Vapor Pressure (kiloPascals)(vap_pres)

• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Time of Minimum Relative Humidity(time_min_rh)
• Time of Maximum Relative Humidity(time_max_rh)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Time of Maximum Vapor Pressure(time_max_vap_pres)
• Maximum Relative Humidity(max_rh)
• Time of Minimum Vapor Pressure(time_min_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - West RH Probe Replacement

On 4-5 November 1997, the Qualimetrics RH probes were removed from the west
elevator 25 and 60 meter levels and replaced with Vaisala probes.  The
Vaisala probes had to be inserted upside down in the Qualimetrics
aspirators to make them fit.  Data during the period above is incorrect.
The west temperature probes appeared to need recalibration, so that was
done on 5 November.  Little improvement in the comparison of west and
southeast carriage temperatures can be detected in the data after 5
November.  RH comparisons show that the west and southeast side Vaisala
probes agree within 1% normally, with only a very occasional 3% to 4%
difference (when RH is greater than 90%).  West side temperatures are normally
greater in the daytime especially, an indication that the aspiration rate in
the west side aspirators is marginal, as I reported when they were installed 5
years ago.  The west side metal aspirators also have more thermal mass than the
plastic southeast aspirators; the combination of this with the lower aspiration
rate causes the west side temperatures to not drop as rapidly as those
measured on the southeast side when the temperature is decreasing.  The west
side temperatures are often 0.2 to 0.6 degrees higher than the southeast
side during the midday.  Obviously, when the temperature differences are large,
the RH tends to be slightly smaller on the west side.

The vapor pressure differences between the west and southeast sides are very
small, 0.03 kPa or less, usually much less, a result that should make the
WVIOP community happy.

• Standard Deviation of Relative Humidity(sd_rh)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Relative humidity inside the instrument enclosure(rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Maximum Relative Humidity(max_rh)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)
• Minimum Relative Humidity(min_rh)

• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Maximum Vapor Pressure(max_vap_pres)
• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - West-side power low

A power outage caused a GFCI breaker to trip.  This removed power from the instruments on 
the tower. Temperature, relative humidity, and the calculated vapor pressure at both 25m 
and 60m levels are suspect because the sensors were not properly aspirated.

• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Vapor Pressure (kiloPascals)(vap_pres)
• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Beam 0 Temperature(temp)
• Standard Deviation of Relative Humidity(sd_rh)
• Relative humidity inside the instrument enclosure(rh)

• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)
• Batter Voltage(vbat)

• Maximum Relative Humidity(max_rh)
• Maximum Temperature(max_temp)
• Minimum Temperature(min_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)
• Minimum Relative Humidity(min_rh)

• Beam 0 Temperature(temp)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Relative humidity inside the instrument enclosure(rh)
• Standard Deviation of Relative Humidity(sd_rh)
• Vapor Pressure (kiloPascals)(vap_pres)

• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Beam 0 Temperature(temp)
• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Minimum Relative Humidity(min_rh)
• Maximum Relative Humidity(max_rh)
• Minimum Temperature(min_temp)
• Maximum Temperature(max_temp)
• Maximum Vapor Pressure(max_vap_pres)
• Minimum Vapor Pressure(min_vap_pres)

SGP/TWR/C1 - West Side 25m RH Zero

On 5 January 1998, decreased battery voltage in the CR21X datalogger for the 25m level of 
the west side of the SGP CF tower apparently damaged the electronics of the RH probe.  
The RH was zero (and the vapor pressure was therefore incorrect) during the period. The RH 
probe was replaced.

• Vapor Pressure (kiloPascals)(vap_pres)
• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Standard Deviation of Air Temperature(sd_temp)
• Standard Deviation of Relative Humidity(sd_rh)
• Beam 0 Temperature(temp)
• Standard Deviation of Vapor Pressure(sd_vap_pres)
• Relative humidity inside the instrument enclosure(rh)

• Aspirator Flow Status (% of time with proper flow)(aspirator)
• Batter Voltage(vbat)
• Vapor Pressure (kiloPascals)(vap_pres)
• Relative humidity inside the instrument enclosure(rh)
• Beam 0 Temperature(temp)