CLIMATOLOGY OF SURFACE-BASED INVERSIONS IN THE NORTH-AMERICAN ARCTIC

The annual cycle of surface-bawd inversions at nine Arctic weather stations is examined, based on a 20-year set of daily 1200 UT significant level radiosonde data. All stations am at or near the coast. Inversions in winter months are primarily the result of strongly negative net radiation at the surface, whereas in summer, inversions more commonly result from near-surface cooling of warm air masses. Inversion frequency is at a maximum in winter (generally >70% of days) when inversions range from approximately 400 to approximately 850 m in thickness. Inversion thickness and strength (temperature change across the inversion) am strongly related to surface temperature. Inversions may involve temperature changes of >30-degrees-C in <1 km, with gradients of >6-degrees-C 100 m-1 during periods of extreme warm air advection aloft. Midwinter inversions commonly persist for 2-4 days, but may remain undisturbed for several weeks, affecting lower tropospheric chemistry.