The annual cycle of surface-based inversions at nine Arctic weather stations is examined, based on a 20-year set of daily 1200 UT significant level radiosonde data. All stations are at or near the coast. Inversions in winter months are primarily the result of strongly negative net radiation at the surface, whereas in summer, inversionsmore commonly result from near-surface cooling of warm air muses. Inversion frequency is at a maximum inwinter (generally >70% of days) when inversions range from -400 to -850 m in thickness. Inversion thickness and strength (temperature change across the inversion) are strongly related to surface temperature. Inversions may involve temperature changes of >30"C in (j"C 100 m,l during periods of eX1rerne warm air advection aloft. Midwinter inversions commonly persist for 2-4 days, but may remain undisturbed for several weeks, affecting lower tropospheric chemistry.