Precipitation data – Pyramid (5035 m asl) and Pheriche (4260 m asl)

Geonor Pyramid
o Location: 5035 m asl. and see the map in AWS Changri information for the exact
location
o Data: checked (and corrected for snow undercatch)
o Displayed Hour = Local time (= TU+5h45)
o Sensors: Geonor T-200BM
o Sensor height : 1.8 m above the ground

Geonor Pheriche
o Location: 4260 m asl. and see the map in AWS Changri information for the exact
location
o Data: checked (and corrected for snow undercatch)
o Displayed Hour = Local time (= TU+5h45)
o Sensors: Geonor T-200BM
o Sensor height : 1.8 m above the ground

Data Treatment
o 1. Noise and evaporation correction: Precipitation at the Pyramid and Pheriche sites
are extracted from the bucket weight, which is recorded with a Geonor T-200BM at
15-minute intervals (or 30 min interval after May 2016). To extract the precipitation
at each time step, we first calculate the change in bucket content, which is supposed
to be always positive given that evaporation is blocked with a layer of oil spread out
over the water. However, the vibrating device used to weigh the bucket is sensitive
to external perturbations such as wind, which results in a background noise i.e. small
positive or negative changes every 15-minute time step. To smooth the signal and
avoid any negative precipitation, we compensate each negative change recorded
over a 15-minute time step by summing it with the neighbouring positive changes. In
this way, the accumulated precipitation recorded over the entire period remains
unchanged. Periods with prolonged evaporation (negative values) are put to 0.
o 2. Correction recommended by WMO: Such kind of device is known to undercatch
precipitation in case of snowfall. So a second treatment is done using Tair data (for
phase discretization: rain vs snow) and wind speed (the correction is largely
dependent on wind speed). This correction following Forland at al. (1996) is
recommended by WMO and has been applied in tropical environments (Lejeune et
al.,2007a,b; Wagnon et al., 2009). The accuracy is estimated at +/-15%.

Data Excel files
o 1. from Dec 2012 to May 2016: cumulated hourly values (date-hour in 1st column),
corrected for noise and evaporation (2nd column) and corrected for undercatch (3rd
column, +/- 15% accuracy) for Pyramid and for Pheriche (4th and 5th columns)
o 2. Since May 2016, same as above for half-hourly values, with also air temperature
(1.6 m), relative humidity (1.6 m), wind speed and direction (1.8 m) at both stations.
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Forland, E. J., Allerup, P., Dahlström, B., Elomaa, E., Jonsson, T., Madsen, H., Perälä, J., Vedin, H. &
Vejen, F. (1996) Manual for operational correction of Nordic precipitation data. Klima Report
N°24/96, DNMI, Nordic Working Group on Precipitation (NWGP).
Lejeune, Y., P. Wagnon, L. Bouilloud, P. Chevallier, P. Etchevers, E. Martin, J.E. Sicart, F. Habets,
Melting of snow cover in a tropical mountain environment: processes and melting, J.
Hydrometeorol., 8, 922-937, Doi: 10.1175/JHM590.1, 2007a.
Lejeune, Y., Y. L’Hôte., P. Etchevers, P. Wagnon, J.P. Chazarin, P. Chevallier, Constitution d’une base
de données météorologiques sur un site andin de haute altitude : le site du Charquini, 4795
m, Bolivie, IAHS Red Book, 318, 173-185, 2007b.
Wagnon, P., M. Lafaysse, Y. Lejeune, L. Maisinsho, M. Rojas & J.P. Chazarin, Understanding and
modelling the physical processes that govern the melting of the snow cover in a tropical
mountain
environment
in
Ecuador,
J.
Geophys.
Res.,
114,
D19113,
doi:10.1029/2009JD012292, 2009.
Photos
Photo 1 : Geonor at Pyramid
Photo 2 : Geonor at Pheriche
On 20 November 2015, 13:45LT at Pheriche and on 22 November 2015, 9:15 LT at Pyramid,
we installed a non-ventilated T/RH sensor (CS215) at 1.6 m above the ground and a wind
speed/direction sensor (Young 05103-5) at the level of the top of the Geonor collector (1.8 m)
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Figure 3: Photo of the Geonor raingauge at Pyramid (22/11/2015, Wagnon)
Figure 4: Geonor raingauge at Pheriche (5/11/2016, Wagnon)
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