Seasonal temperature changes with elevation on Mount Washington

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Wells, Meghan
The summit of Mount Washington is warming more slowly than surrounding lower elevations of the Northeast, which is opposite to climate model projections and observations in other mountain ranges. A looming scientific question is: why? A hypothesis is that the exposure of the summit to the "free troposphere," an air mass that sits above the ground-based "boundary layer," for approximately half the year is imparting a slower warming at the summit. This research project takes a preliminary first step toward answering this question by finding methods to determine when Mount Washington is in the boundary layer. Temperature readings from the summit, and the bases of the Cog Railway (west side) and Auto Road (east side) from 2015-2016 were used to calculate lapse rates. Lapse rates were plotted for their monthly and seasonal variability. For daily variability, the lapse rates were low at night and increased during the day. Spring and summer were found to have to greatest lapse rates compared to fall and winter months. During the spring and summer the sun is higher in the sky, which leads to more warming of the ground and greater vertical motions that grow the boundary layer to the summit altitude frequently.