the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Foehn Winds at Pine Island Glacier and their role in Ice Changes
Ricardo Fonseca
Kyle S. Mattingly
Stef Lhermitte
Catherine Walker
Abstract. Pine Island Glacier (PIG) has recently experienced increased ice loss mostly attributed to basal melt and ocean-ice dynamics. However, atmospheric forcing also plays a role in the ice mass budget, as besides lower-latitude warm air intrusions, the steeply sloping terrain that surrounds the glacier promotes frequent Foehn winds. An investigation of 41-years of reanalysis data reveals that Foehn occurs more frequently from June to October, with Foehn episodes typically lasting about 5 to 9 h. An analysis of the surface mass balance indicated that their largest impact is on the surface sublimation, which is increased by about 1.4 mm water equivalent (w.e.) day−1 with respect to no-Foehn events. Blowing snow makes roughly the same contribution as snowfall, around 0.34–0.36 mm w.e. day−1, but with the opposite sign. The melting rate is three orders of magnitude smaller than the surface sublimation rate. The negative phase of the Antarctic Oscillation and the positive phase of the Southern Annular Mode promote the occurrence of Foehn at PIG. A particularly strong event took place on 09–11 November 2011, when 10-m winds speeds in excess of 20 m s−1 led to downward sensible heat fluxes higher than 75 W m−2 as they descended the mountainous terrain. Surface sublimation and blowing snow sublimation dominated the surface mass balance, with magnitudes of up to 0.13 mm w.e. hr−1. Satellite data indicated an hourly surface melting area exceeding 100 km2. Our results stress the importance of the atmospheric forcing on the ice mass balance at PIG.
Diana Francis et al.
Status: final response (author comments only)
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RC1: 'Comment on tc-2023-46', Anonymous Referee #1, 23 Apr 2023
Publisher’s note: a supplement was added to this comment on 24 April 2023.
- AC1: 'Reply on RC1', Diana Francis, 19 May 2023
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RC2: 'Comment on tc-2023-46', Anonymous Referee #2, 25 Apr 2023
Pine Island Glacier is a major contributor to the loss of ice mass. Work to date has focused on understanding basal melting. The authors use 41 years of reanalysis data to investigate the role of Foehn winds in the surface mass balance at Pine Island Glacier. They characterise Foehn episodes over the satellite record and show that sublimation plays an important role in surface mass balance. Sublimation processes are not captured existing remote sensing techniques and this article highlight an important contribution to ice mass balance that is currently not monitored.
The article is well-written and well-structured. It is an interesting article that provides a new aspect to our understanding of how Pine Island Glacier is changing in defining the role of Foehn winds in surface melting. My comments are largely related to improving the readability of the figures and the length of the article.
My one main concern is around confidence in the ERA5 dataset. The authors note that ERA5 does not have a sufficient spatial resolution to fully resolve smaller-scale flows. However, they also note that previous work has shown that moderate to strong Foehn events can be identified over the Antarctic Peninsula. Does this location of the AWS allow an assessment of the proportion of Foehn events at PIG that are resolved in ERA5? If this could be shown, it would lend more weight to the conclusions.
It is a long article, and the authors might consider some of the following suggestions to reduce the length of the article:
- Introduction - you later show that SAM does not play a large fole in the weather conditions at PIG, so perhaps you don’t need to include the details on SAM in the introdution (lines 116-121).
- Less emphasis in the introduction on Foehn processes around Antarctica and instead focus on an introduction to the important details in and around Pine Island Glacier. Similarly in section 3, the Foehn events at Pine Island Glacier are extensively compared to Foehn events elsewhere. Some of the details from other locations can be more concisely presented and the focus kept on what is happening at Pine Island Glacier.
- Lines 334-345 there is a long discussion about trends. With the amount of variability in the signals, the timeseries is too short to identify a trend. Consider just pointing out the small trends and low statistical significance
Minor comments
Figure 1a: it is very difficult to differentiate between the thick and thin purple lines - perhaps consider using two colours. I find the purple quite hard to read on the dark green so maybe a different colour scheme would also help here. Perhaps you could show the location of the Evans Knoll AWS on Figure 1a. It would also be help to orient the reader if you could show the location of the outline for Figures 3 and 4 on this figure - I don’t think they are the same as the red box shown?
Figure 2a and b: I found it tricky to related the yellow boxes to the red axis and it took me a while to work out how to read these graphs. Consider using the same colors for the bars and/or adding a legend as you do in Figure 2c.
Citation: https://doi.org/10.5194/tc-2023-46-RC2 - AC2: 'Reply on RC2', Diana Francis, 19 May 2023
Diana Francis et al.
Diana Francis et al.
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