Methods and procedures
Temperature readings are taken with submerged U-shaped max/min
thermometer placed in evaporation pan on south side to maximize
shade. Max/min values are reset using magnet kept at pan. A
micrometer hook gage is used to measure initial water level and
final water level (after evaporation). Total rainfall since last
reading is obtained from adjacent standard rain gauge for which
rainfall is recorded after each event. Data is recorded on data
sheets and, beginning 11 June 2011, entered using KeyesPunch Data
Entry software. This data is appended to a Microsoft Excel file,
evap-pan.xls. The variables interval_days and begin_period are
calculated and determined, respectively, once in the Excel file. The
evaporation is calculated based on evaporation period determined by
begiPeriod and dateRead dates. Calculated evaporation is (i-water
minus f-water). A comma-separated-file (CSV) is generated for final
output.
Quality assurance (QA): Beginning 11 June 2011, entries are
validated based on acceptable values during data entry. The Quality
Flag is autogenerated based on entries, visually checked, and
assigned to each data record. Data is verified using double-entry
method with KeyesPunch Data Entry software. Prior to this,
verification was a visual check after data was entered into an Excel
spreadsheet.
Evaporation = (initial H2O level + rainfall - final H2O level)
Rainfall collected in the graduated rain gauge data used until
07/07/92 was protected from evaporation by addition of mineral oil.
Rainfall collected in standard can rain gauge located at LTER
Weather Station (used after this date due to proximity to
evaporation pan) is subject to low evaporation because mineral oil
cannot be added to this type gauge. However, it is typically
measured within 24 hours of a rain event and evaporation has been
found to be negligible.
Location of pan and precip gauge:
These have changed slightly over time (per the Dataset Documentation
file).
Evaporation pan location:
12 Jul 1983 to 10 Oct 1991: Approximately 1/2
mile S from Jornada LTER Weather Station about 100 meters downslope
from LTER-II C-CALI Lizard Pitfall grid within 10 meters of road
leading up to powerline and within creosotebush zone.
10 Oct 91 to Present: Relocated to Jornada LTER
Weather Station which is located about 1/2 mile SE of NMSU College
Ranch Headquarters in mixed-forb and grassland area about 200m from
creosotebush transition zone. This is approximately 840 meters north
of the previous location.
Rain gauge location:
12 Jul 1983 to 07 Jul 1992: Approximately 1/2
mile SE of NMSU College Ranch Hdqr at LTER Upper Trailer (Graduated
rain gage)
08 Jul 1992 to Present: Standard Rain Gauge at
Jornada LTER Weather Station.
