Abstract:
These data were collected under a collaborative arrangement between the Australian Antarctic Division (Principal Investigator: Gary Burns) and the Russian Antarctic Expeditions (Chief Russian Investigator: Oleg Troshichev, Institute of Arctic and Antarctic Studies, St Petersburg).
Vertical electric field data were collected with an electric field mill (EFM) at Vostok intermittently over the ... interval 1998-2004. [A different electric field mill was installed at Vostok in late December 2006, and metadata from this instrument is found at ASAC_974_2]. The data were initially collected with 10 second resolution. The EFM is calibrated monthly by placing a Faraday box containing parallel plates over the rotating dipole. A range of voltages are applied to the plates and the instrument is calibrated in volts per metre relative to the calibration box. Absolute values are not possible to determine, as the instrument compression is unknown. The values should be treated as relative.
An additional factor to be noted is the height of the EFM. When it was initially installed, it was on a metal pole ~1.5 m above the snow surface. When the site was visited in December 2005, the height of the pole indicated the instrument would have been 1.05m above the snow surface. A change in height will alter the instrument compression (higher height implies larger instrument compression). It would be extremely difficult to accurately interpret these data to determine a long term trend.
The 10 second resolution data have been averaged to yield minute resolution values. Calibrations are linearly interpolated and have been applied to the data.
1 minute averages are provided in this download for 1998-2004. 10 second averages are provided for 2005-2006.
Files of the form "VEFCalibrationInfo_1998.txt" indicate the calibration data that has been applied to each year.
Any data for any month is in files of the form: "VosEF_1998_01.txt", where "1998" indicates the year and "01" indicates the month.
The monthly data files list the data as "Year,DoY,UT Hour,UT Min,EF-all(V/m),EF-fair(V/m)". This is the also the first line of each monthly file. "Year" is a 4 digit representation of the year. "DoY" is the day-of-year number from 1 to 365/366. "UT Hour" is the Universal Time hour for the observation. "UT Min" is the Universal Time minute for the observation. "EF-all(V/m)" is the electric field value determined for that minute, with the calibration applied, independent of whether the data are selected as 'fair-weather'. "EF-fair(V/m)" is the electric field value determined for that minute, with the calibration applied, IF that data has been selected as 'fair-weather'.
An outline of how 'fair-weather' has been determined is given in the publication: Burns, G.B., Frank-Kamenetsky, A.V., Troshichev, O.A., Bering, E.A., Reddell, B.D. (2005) Interannual consistency of bi-monthly differences in diurnal variations of the ground-level, vertical electric field. Journal of Geophysical Research 110, D10106. doi:10.1029/2004JD005469.
The data are comma delimited in the monthly processed data files. Thus the line
1998,60,0,25,179.14,179.14 means a fair-weather value of 179.14 volts per metre (relative to the calibration box) is determined for the 25th minute, of the zeroth UT hour, of the 60th day of the year 1998.
1998,60,3,7,244.75, means a value of 244.75 volts per metre (relative to the calibration box) is determined for the 7th minute, of the 3rd UT hour, of the 60th day of the year 1998; and that this value is not determined to be 'fair-weather'.
The monthly processed data files list every minute for the month, even if there is no value for that minute. A lack of data is indicated by an absence of values, but a retention of the separating comma.
Thus the line 1998,62,16,8,, indicates that no values were recorded for the 8th minute, of the 16th UT hour, of the 62nd day of the year 1998.
'Fair-weather' data were recorded at Vostok ~55% of the time the instrument was operational, but there are seasonal and summer diurnal variations. [See previous reference]. Please note: Vostok is a difficult operational environment and the electric field mill suffered considerable intervals of instrument failure. If there is no monthly file, then no data were recorded for that month.
Vostok was not occupied during 2003, so no data exists for that time.
The electric field mill used to collect these data incorporated carbon brush commutators to rectify the signal from the rotating dipole. Over the years of operation, wear on these led to greater variability in the monthly calibrations. As discussed in the paper previously referenced, the monthly calibration data for 2002 were twice as variable as any of the earlier years and thus only data from the years 1998 through 2001 were combined to yield seasonal-diurnal averages. The 2004 data (not available at the time of the referenced analysis) have a large monthly variability, but not as great as 2002. When utilising the data, these difficulties need to be considered. The yearly calibration data files can be used to quantify the level of uncertainty in the measurements.
Quality
Vostok electric field (EF) data analysis has been processed by linearly interpreting between calibration measurements. See the calibration files for further information.
Specific caveats on the Vostok EF data:
They are calibrated only to the calibration box, NOT absolutely.
They should not be used for long-term trend analysis ...when the Electric Field Mill ... (EFM) was installed on a metal post in 1998 it was 1.5m above the snow surface. In January 2006 the EFM on the pole was ~1.05 m above the snow surface. The compression factor over the years would be changed by a variable amount.
History of Vostok EF data:
There are no data from 2003; Vostok was not occupied that winter.
A new EFM was only installed at the end of 2005, after the old EFM became very unreliable towards the end of 2004. Unprocessed data (10s resolution - no selection for 'fair-weather') are available at ASAC_974_2
Email:
Jaqueline.A.Richter-Menge at erdc.usaec.army.mil
Contact Address:
Cold Regions Research and Engineering Laboratory
72 Lyme Rd.
City:
Hanover
Province or State:
NH
Postal Code:
03755-1290
Country:
USA
Publications/References
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Coauthors (2006), Greenland ice sheet surface mass balance variability (1988–2004) from calibrated Polar MM5 output., J. Climate, 19, 2783–2800
Cappelen, J., Ed. (2009), DMI monthly climate data collection 1768-2008, Denmark, The Faroe Islands and Greenland, Tech. Rep. 09-05, 53 pp., Dansk Meterologisk Institut
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