Self‐regulated fluctuations in the ablation of a snow patch over four decades

[1] We describe four decades of temporal fluctuations in the ablation of the Hamaguri-yuki snow patch in the northern Japan Alps. Annual ablation depth through the melting season shows a significant correlation with the initial depth (at the beginning of the melting season), whereas a less significant correlation is found with a temperature index that is generally believed to correlate well with ablation. The scale effect of the snow patch, which appears to modify the wind speed over the patch, has a more significant effect on snow ablation than does the radiation shadowing effect of surrounding mountains. In the case of a thinner and therefore smaller initial springtime snow patch, the speed of the local wind may be reduced over the snow surface, thereby suppressing ablation, whereas wind speed is not reduced (and ablation is not suppressed) in the case of a thicker snow patch. This self-regulating feedback means that over the past four decades, the thickness of the snow patch has fluctuated in a manner that is largely independent of summertime temperature. Our findings also suggest that the self-regulating feedback, which influences ablation, allows some small wind-drifted glaciers to survive, whereas previous studies reported enhanced accumulation at such glaciers via a similar topographic effect on wind speed and suppressed ablation via the shading effect of surrounding mountains on solar radiation.