RH

High frequency measurements from Canada Glacier Meteorological Station (CAAM), McMurdo Dry Valleys, Antarctica (1994-2022, ongoing)

Abstract: 

As part of the McMurdo Dry Valleys Long Term Ecological Research program, meteorological data are collected from various locations throughout the McMurdo Dry Valleys of Antarctica. This package contains 15-minute data from the Canada Glacier Meteorological Station (CAAM), located in Taylor Valley (Latitude: -77.61334, Longitude: 162.96437, Elevation: 264 meters above sea level). CAAM was established in 1994, during the 94/95 field season. 

LTER Core Areas: 

Dataset ID: 

7006

Associated Personnel: 

814
808
344
22
154
155

Related publications: 

McMurdo Dry Valleys Long-Term Ecological Research (LTER): LTER automatic weather network (LAWN)

Related links: 

Meteorological Task Lists

Short name: 

CAAM

Purpose: 

Meteorological data are collected year-round at each of MCM LTER stations. Data are manually downloaded from the meteorological stations during the austral summer. Raw 15 minute data (Level 0) is processed and provided as Level 1 data on the MCM LTER website. Field notes, sensor information, processing procedures, QA/QC, and metadata is provided in the Meteorological Post Processing Documentation and Task Lists for each field season at the following address: https://mcm.lternet.edu/meteorological-task-lists 

Locations: 

Canada Glacier Meteorological Station

Data sources: 

CAAM_AIRT
CAAM_AIRT3ASP
CAAM_RADN
CAAM_RH
CAAM_SURFTEMP
CAAM_WIND
CAAM_ICET
CAAM_PRESSTA

Methods: 

On December 1, 1994, Gayle Dana established a summer-only eddy correlation station on Canada Glacier. The station and program both  belonged to Scott Tyler at the Desert Research Institute (DRI) so they were slightly different than the LTER standard. However, the station was set up to  monitor all of the standard meteorological parameters, as well as net radiation and sensible and latent heat fluxes with the use of the eddy correlation sensors  during the summer. Information was gathered with a sampling frequency of every 1 second and averaging & output interval of every 20 minutes using this  setup from December 1, 1994 to January 21, 1995. 
 
On November 20, 1995, Karen Lewis established a permanent meteorology station  on Canada Glacier with eddy sensors. It was set up to sample sensors regularly 
and send summary statistics (for example, averages and maximums) to solid-state storage modules every: 
 
 
  15 minutes between November 20, 1995 and January 16, 1997, 
  15 minutes between January 12, 1998 and January 16, 1998, 
  10 minutes between January 16, 1998 and January 30, 1998, 
  15 minutes thereafter. 
 
  
This has resulted in approximately 20 values being recorded for final storage in every output interval. 
 
(NOTE: Between Jan 16, 1997 @ 09:30 and Jan 12, 1998 @ 21:15 the  station was taken down and brought to the U.S. It was taken back to Antarctica for the 1997-98 season andamp; set up on January 12, 1998). 
 
  Sampling and Averaging Intervals
   
    For Sampling frequency and Data Logger output and averaging intervals please visit:
    
 

Maintenance: 

 
Data and metadata imprivded using the DEIMS management system on 2014, Inigo.
 
 Files were submitted by Karen Lewis to the McMurdo LTER data manager in October, 1997 and  March, 1999. In order to get the dates and times in the proper format, Denise Steigerwald changed any times marked as 24:00 to 0:00, and added 1 to the corresponding julian date. Julian dates and times were then converted to a format with mm/dd/yy hh24:mm in order to make this file more compatible with other McMurdo LTER files. Variables were renamed to match with corresponding measurements at other meteorology stations. A column was also added for
 location code in order to identify the station of these measurements. Updates were done using Microsoft Excel and Access software. Comma delimited ascii files were then generated to make the data files available on the web page.
 
In June, 1999, it was determined that the transformations used to get records from level 0 to level 1 did not occur for the data sets submitted by Karen Lewis. Denise Steigerwald, the data
 manager, therefore replaced what she could with data sets that originated at the Desert Research Institute and had undergone these transformations. This included records between November 10, 1995 and August 21, 1996. The remaining records were downloaded by Thomas Nylen to allow him to get the records to level 1. On September 29, 1999, the level 1 records on the web replaced the level 0 records.
 
 In May 2000, the 1999-2000 data was posted. In the process, Denise Steigerwald changed the layout of the files so that they were sorted by category (air temperatures, humidity, radiation, wind etc.) rather than by year. Files containing monthly and daily averages were generated and minor adjustments were made to the metadata.
 
 On May 17, 2000, relative humidity (RH) values were corrected for a systematic error in the measurement created by an instrument manufacturer error. All RH data with air temperatures below freezing were corrected using the vapor pressure over ice (rather than over water which was used initially). The error became quite large for very cold temperatures (the correction could grow to around 30%). The formula used for the correction was:
 
 RH_corr=RH_orig/((A*temp*temp)+(B*temp)+C)
 where
 RH_corr = corrected relative humidity
 RH_orig = original relative humidity
 temp = air temperature
 A = 4.165E-5
 B = 9.7E-3
 C = 1.0
 For example, with an air temperature of -2.3 and RH_orig of 50.6, the RH_corr will be 51.7. Records that showed corrected RH values greater than or equal to 100 were changed to 99.99 and flagged.
 
 In June 2000, summary files were added to the web containing daily and monthly statistics.  These were generated by creating "views" of daily and monthly means, minimums, maximums and counts of the records represented in the Oracle database's meteorology tables.
 
 On June 4, 2004, the relative humidity (RH) values after January 16, 2000 @ 1600 were corrected for a systematic error in the measurement created by an instrument manufacturer error.
 
 All RH data with air temperatures below freezing were corrected using the vapor pressure over ice (rather than over water which was used initially). The error became quite large for very cold  temperatures (the correction could grow to around 30%). The polynomials used for the  correction is based on Lowe (1977). The original RH value is multiplied by the saturation vapor pressure over water and divided by the the saturation vapor pressure over ice 
 
 RH3m_corr=[RH3m]*(6.107799961 + [AirT3m] * (0.4436518521 + [AirT3m] *  (0.01428945805 + [AirT3m] * (0.0002650648471 + [AirT3m] *(0.000003031240396 + [AirT3m] * (0.00000002034080948 + 0.00000000006136820929 * [AirT3m])))))) /  (6.109177956 + [AirT3m] * (0.503469897 + [AirT3m] * (0.01886013408 + [AirT3m] * (0.0004176223716 + [AirT3m] * (0.00000582472028 + [AirT3m] * (0.00000004838803174 + 0.0000000001838826904 * [AirT3m])))))))
 
Records that showed corrected RH values greater than or equal to 100 were changed to 99.99  and flagged.
 
July 2023: It was discovered that the 3m aspirated air temperature measurements from 2012-01-04 16:30 onward were actually 1m air temperature measurements. This error has been corrected, and the AIRT and AIRT3ASP data files have been updated accordingly.
 

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