In situ observed relationships between snow and ice surface skin temperatures and 2 m air temperatures in the Arctic
<p>To facilitate the construction of a satellite-derived 2 m air temperature (<span class="inline-formula"><i>T</i><sub>2 m</sub></span>) product for the snow- and ice-covered regions in the Arctic, observations from weather stations are...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-03-01
|
| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/13/1005/2019/tc-13-1005-2019.pdf |
| Summary: | <p>To facilitate the construction of a satellite-derived 2 m air temperature
(<span class="inline-formula"><i>T</i><sub>2 m</sub></span>) product for the snow- and ice-covered regions in the
Arctic, observations from weather stations are used to quantify the
relationship between the <span class="inline-formula"><i>T</i><sub>2 m</sub></span> and skin temperature
(<span class="inline-formula"><i>T</i><sub>skin</sub></span>). Multiyear data records of simultaneous <span class="inline-formula"><i>T</i><sub>skin</sub></span>
and <span class="inline-formula"><i>T</i><sub>2 m</sub></span> from 29 different in situ sites have been analysed for
five regions, covering the lower and upper ablation zone and the accumulation
zone of the Greenland Ice Sheet (GrIS), sea ice in the Arctic Ocean, and
seasonal snow-covered land in northern Alaska. The diurnal and seasonal
temperature variabilities and the impacts from clouds and wind on the
<span class="inline-formula"><i>T</i><sub>2 m</sub></span>–<span class="inline-formula"><i>T</i><sub>skin</sub></span> differences are quantified.
<span class="inline-formula"><i>T</i><sub>skin</sub></span> is often (85 % of the time, all sites weighted equally)
lower than <span class="inline-formula"><i>T</i><sub>2 m</sub></span>, with the largest differences occurring when the
temperatures are well below 0 <span class="inline-formula"><sup>∘</sup></span>C or when the surface is melting.
Considering all regions, <span class="inline-formula"><i>T</i><sub>2 m</sub></span> is on average
0.65–2.65 <span class="inline-formula"><sup>∘</sup></span>C higher than <span class="inline-formula"><i>T</i><sub>skin</sub></span>, with the largest
differences for the lower ablation area and smallest differences for
the seasonal snow-covered sites. A negative net surface radiation balance generally cools
the surface with respect to the atmosphere, resulting in a surface-driven
surface air temperature inversion. However, <span class="inline-formula"><i>T</i><sub>skin</sub></span> and
<span class="inline-formula"><i>T</i><sub>2 m</sub></span> are often highly correlated, and the two temperatures can
be almost identical (<span class="inline-formula"><0.5</span> <span class="inline-formula"><sup>∘</sup></span>C difference), with the smallest
<span class="inline-formula"><i>T</i><sub>2</sub></span>–<span class="inline-formula"><i>T</i><sub>skin</sub></span> differences around noon and early afternoon during
spring, autumn and summer during non-melting conditions. In general, the
inversion strength increases with decreasing wind speeds, but for the sites
on the GrIS the maximum inversion occurs at wind speeds of about
5 m s<span class="inline-formula"><sup>−1</sup></span> due to the katabatic winds. Clouds tend to reduce the vertical
temperature gradient, by warming the surface, resulting in a mean overcast
<span class="inline-formula"><i>T</i><sub>2 m</sub></span>–<span class="inline-formula"><i>T</i><sub>skin</sub></span> difference ranging from <span class="inline-formula">−0.08</span> to
1.63 <span class="inline-formula"><sup>∘</sup></span>C, with the largest differences for the sites in the
low-ablation zone and the smallest differences for the seasonal snow-covered
sites. To assess the effect of using cloud-limited infrared satellite
observations, the influence of clouds on temporally averaged
<span class="inline-formula"><i>T</i><sub>skin</sub></span> has been studied by comparing averaged clear-sky
<span class="inline-formula"><i>T</i><sub>skin</sub></span> with averaged all-sky <span class="inline-formula"><i>T</i><sub>skin</sub></span>. To this end, we
test three different temporal averaging windows: 24 h, 72 h and 1 month.
The largest clear-sky biases are generally found when 1-month averages are
used and the smallest clear-sky biases are found for 24 h. In most cases,
all-sky averages are warmer than clear-sky averages, with the smallest bias
during summer when the <span class="inline-formula"><i>T</i><sub>skin</sub></span> range is smallest.</p> |
|---|---|
| ISSN: | 1994-0416 1994-0424 |