Atmospheric layering during peak pine pollen season

Abstract

Pollen release by Northern Hemisphere pine forests is well-documented yet little is known about its atmospheric layering. At what altitudes are these atmospheric layers and how do they influence pollen dispersal? To answer this, pollen concentrations were analysed using radiosonde soundings and LiDAR imagery over the Pamlico Sound, a large marine body at 35.4062° N, 76.3259° W between coastal of North Carolina, USA and its barrier islands. Pollen sampled over the sound ranged from 11 to 861 pollen m−3. During daylight, the planetary boundary layer (PBL) height was 1932 m and it was capped by a warm, dry inversion from 2015 to 3072 m. Similarly, PBL height was estimated at 2000 m using a CALIPSO LiDAR image. Mixed-phase clouds could form above the PBL starting at 5650 m where temperatures were less than −13.5 °C and wind speeds exceeded 29.8 m s−1. During cooler night hours, the PBL height dropped to 724 m and its inversion cap also dropped to 1027–1904 m. Strong westerly winds with a low vertical shear drove pollen across water on a cloudless sunny day. Wind speeds below the PBL stayed strong at night while rising relative humidity influenced pollen deposition. Structuring atmospheric layers during pollen dispersal provided more understanding of how long-distance pollen is dispersed at a land–atmosphere interface.