No really – it’s May.
2009-05-11 18:44:47.000 – Ali Boris, Summit Intern
Looking west at the mixing layer above the summit
No really – it’s May.
We awoke yesterday morning to a wintry scene rather than the sedgey, golden mountaintop of the night before. I finally experience a thunderstorm up here on Saturday night, though! Friday night, Mike and I took a hike which ended at Nelson Crag in time to watch a big cumulonimbus with real lightning potential roll by, but the big event came as Ryan predicted the following night. The observers claimed that the storm was only a two on the one-to-ten scale, but I was nevertheless very excited to be on the inside of a thunderstorm. Lightning struck the nearby radio tower a few times with thick, brilliantly pink streaks. The sound was dampened by the wind and moisture so that we only heard a few strikes. As Ryan described, they sounded like trash can lids being clanged together.
After the excitement of convective and winter storms, the summit has cleared out today to reveal a mixing layer extending to about 400 feet above us. As some of you may have read in one of my past comments, my research up here has been mainly centered on estimating the depth of the boundary layer. The overall purpose of my study has been to explain trends in the fine particulate matter data from Lakes of the Clouds and Camp Dodge, but I’ve also been finding out some interesting things about the boundary layer itself. In taking an online course which explains the wind patterns and boundary layer development in mountainous regions, I learned that the daytime layer actually develops earlier and more quickly on hills and mountains because the sun’s morning radiation hits them first, causing longwave radiation to heat and move the air above the ground at the highest points. The boundary layer deepens throughout the day, eventually evening out a bit in depth.
According to the NOAA Stability Time Series model (which may not be all that accurate here in the mountains, but it’s an approximation!), our mean summer boundary layer height is 1042 m, or 3418 feet above sea level. I’ve also calculated that the boundary layer (given flat terrain) reaches above the summit on 33% of summer days. Considering that boundary layer development over a mountain will be deeper than that over flat terrain, that number should be a bit bigger -but other studies have suggested that it should be over the summit on most days. While my model results may not be right on, other authors have only looked at the region in general. Who’s right? Hopefully someday we’ll be able to measure the boundary layer right here along the profile of the mountain and this question will be answeredâ€¦ For now, it’s interesting to watch where the boundary layer appears on our horizon and hope that what I’m doing will be helpful to other folks working on this question in the future.
Ali Boris, Summit Intern