Solar Eclipse Impacts on Planetary Boundary Flow

The annular and total solar eclipses of 14 October 2023 and 8 April 2024 across the United States presented a rare opportunity to study eclipse impacts on the planetary boundary layer (PBL). As a part of the NASA-funded Nationwide Eclipse Ballooning Project, 19 atmospheric science ballooning teams dispersed along the eclipse paths and released 30 weather balloons each, once per hour starting 24 hours prior to the eclipse peak and ending 6 hours after. A ground weather station measured solar radiation, temperature, relative humidity, pressure, and wind speed and direction.

The two teams from Plymouth State University in New Hampshire traveled to Moriarty, New Mexico and Pittsburg, New Hampshire for the annular and total eclipses, respectively. Measurements taken for 24 hours leading up to the eclipses characterize the typical evolution of the diurnal and nocturnal PBL at these locations. At both locations, skies were clear during the entire 30-hour period and the synoptic scale pressure gradients were relatively weak, thus allowing the topography and local radiation budgets to drive the PBL flow.

Moriarty, New Mexico, lies in a mainly flat, broad valley surrounded by mountain ranges to the west, north, and east. Preferential solar heating of these mountain slopes on the morning of the eclipse drove a valley flow that turned with the sun. The annular solar eclipse weakened this valley flow, and the wind direction backed from south to southeast toward the mountain slopes that had received the most insolation that morning.

Pittsburg, New Hampshire lies in a narrow east-to-west oriented section of the Connecticut River. During the night prior to the eclipse, katabatic flow filled the valley with cold air that began to flow westward down the valley about one hour after sunset. During the day, the synoptic scale pressure gradient drove a northwest wind that persisted during the total eclipse, but the wind speed weakened from 4 m/s to <1 m/s. The valley began to fill with cold air, however, insolation returned before a valley flow could develop. A valley flow developed quicker than the previous night, possibly because of residual cold air from the eclipse.