DOI: 10.5061/dryad.f7m0cfxz9
title: Data from: Temporal variability in snow accumulation and density at Summit Camp, Greenland ice sheet

description: A 3-year record of weekly snow water equivalent (SWE) accumulation at
 Summit Camp, central Greenland ice sheet, obtained by direct sampling, is
 presented. While the overall SWE accumulation of 24.2 cm w.e. a−1 matches
 long-term ice core estimates, variability increases at shorter timescales.
 Half of the annual SWE accumulation occurs during a few large events, with
 the average accumulation rate decreasing 35% between the first and second
 halves of the record coinciding with exceptional anticyclonic conditions
 in the spring and summer of 2019. No seasonality in accumulation is
 detected. Rather, local accumulation rates appear to be significantly
 impacted by wind redistribution that obscures temporal patterns in
 snowfall. Surface snow density is consistent, on average, with previously
 measured values but does not correlate with near surface temperature or
 wind speed. Two surface mass balance reanalysis models significantly
 underestimate accumulation rates at Summit Camp. This is concerning
 because such models are often used to estimate ice-sheet mass loss.
description: A shallow, rectangular pit is excavated, and a piece of plywood
 is placed over the floor of the pit. The pit is then allowed to fill with
 snow and settle over a period of 2 weeks. A plastic tube is used to remove
 a core sample of the snow from the surface to the plywood, which serves as
 a depth reference for each subsequent sample. The sample is taken from a
 different location on the board each time, as measured from flagged poles
 at the corner of the plywood, to provide an undisturbed sample. The snow
 water equivalent (SWE) of the sample is obtained from both its mass and
 water volume, providing redundancy for quality control. To obtain the SWE
 thickness of the sample from its mass, the sample is brought indoors in
 its sampling tube and weighed. The weight of the empty sampling tube is
 subtracted, and this weight is divided by the cross-sectional area of the
 tube. To obtain the SWE thickness from the sample volume, the sample is
 allowed to melt and the liquid volume is divided by the cross-sectional
 area of the core. The snow depth at each sampling site is also recorded.
 The SWE estimate divided by this depth gives an estimate of sample
 density. When no
 undisturbed locations remain on the board, or the snow becomes too deep to
 sample, sampling moves to a new, adjacent snow board site. During the
 change to a new site, samples are taken at the same time at both the old
 and new sites. These are termed tie points. Subtracting the SWE value of
 the tie point at the new site from that of the old site, and adding this
 difference to later measurements, gives the cumulate change in SWE across
 site transitions. The snow board sampling sites were in a designated
 area of undisturbed snow, upwind of other field instrumentation and
 buildings to minimize their influence on
 accumulation.
description: From README_SWE_sample_logsheet.txt
 <strong>DATA & FILE
 OVERVIEW</strong> <strong>1. Description of
 dataset</strong> Observations were obtained using
 the snow board method, where accumulation atop a board, which serves as a
 depth reference, is repeatedly sampled and measured. A shallow,
 rectangular pit is excavated, and a piece of plywood is placed over the
 floor of the pit. The pit is then allowed to fill with snow and settle
 over a period of at least two weeks. A plastic tube is used to remove a
 core sample of the snow from the surface to the plywood, which serves as a
 depth reference for each subsequent sample. The sample is taken from a
 different location on the board each time, as measured from flagged poles
 at the corner of the plywood, to provide an undisturbed sample. The snow
 water equivalent (SWE) of the sample is obtained from both its mass and
 water volume, providing redundancy for quality control. To obtain the SWE
 thickness of the sample from its mass, the sample is brought indoors in
 its sampling tube and weighed. The weight of the empty sampling tube is
 subtracted, and this weight is divided by the cross-sectional area of the
 tube. To obtain the SWE thickness from the sample volume, the sample is
 allowed to melt and the liquid volume is divided by the cross-sectional
 area of the core. The snow depth at each sampling site is also recorded.
 The SWE estimate divided by this depth gives an estimate of sample
 density. Measurement precisions and resulting uncertainties are provided
 in Howat (2022). When no undisturbed locations remain
 on the board, or the snow becomes too deep to sample, sampling moves to a
 new, adjacent snow board site. During the change to a new site, samples
 are taken at the same time at both the old and new site. The snow board
 sampling sites were in a designated area of undisturbed snow, upwind of
 other field instrumentation and buildings to minimize their influence on
 accumulation. <strong>2. Data File
 Desription:</strong> File Name:
 SWE_sample_logsheet.txt File Description: Weekly
 Snowboard Measurements File Format: tab-delimited
 text Missing values = -999
 <strong>3:
 Date Field Descriptions</strong>
 Field 1: "Measurement Date (YYYYMMDD)"
 Field 2: "Sample Site ID", Letters identifying each
 snow board used for sampling. Field 3: "Sample
 Distance (cm)", Distance of the sample from the corner of the
 board. Field 4: "Beginning Weight (g)",
 Weight of empty sampling tube. Field 5: "Total
 Weight (g)", Weight of sample and sampling tube.
 Field 6: "Snow Weight (g)", Total Weight minus
 Beginning Weight. Field 7: "Water Volume
 (mL)", Sample water volume after melting. Field 8:
 "Snow Depth (cm)", Thickness of snow above board at sampling
 site. Field 9: "Core Diameter (cm)", Diameter
 of sampling tube. Field 10: "Comments", Notes
 by sampling personnel.