Fog type classification using a modified Richardson number for Christchurch, New Zealand

Situated on a coastal plain between the Southern Alps and Banks Peninsula, Christchurch, New Zealand, experiences around 49 fog days every year. Given its complex topography, accurate forecasting is difficult at Christchurch International Airport (CHA). Climatological analysis of local events an important first step to gain insight into processes involved in lifecycle. In this study, were identified using 12 years meteorological observations from automatic weather station situated CHA. A novel type classification method was developed modified Richardson number (MRi). The MRi assesses dynamic stability 1.25 m shallow layer near-surface air. Here, used as quantitative index classify advection fog, advection–radiation radiation fog. Vertical gradients air temperature wind speed derived for prefog periods, criteria applied classification. results examined correspondence with intensity, duration, diurnal seasonal variability frequency occurrences, synoptic flows. agreement other studies across world, occurs most frequently during winter spring. Radiation predominant CHA, formation development usually coincide drainage northwesterlies. This study use long-term observational data investigate climatology typology CHA detail. climatological characteristics presented will serve basis future Christchurch. can potentially be characteristic worldwide.