Boundary-layer height and surface stability at Hyytiälä, Finland, in ERA5 and observations

Abstract. We investigate the boundary-layer (BL) height at Hyytiälä in southern Finland diagnosed from radiosonde observations, a microwave radiometer (MWR) and ERA5 reanalysis. Four different, pre-existing algorithms are used to diagnose BL radiosondes. The is sensitive method used. level of agreement, sign systematic bias between four different methods, depends on surface-layer stability. For very unstable situations, median radiosondes varies 600 1500 m depending which applied. Good agreement using Richardson-number-based methods found for almost all stability classes, suggesting that has adequate vertical resolution near surface resolve structure. However, overestimates stable conditions, highlighting ongoing challenge numerical models correctly BL. Furthermore, differs most 18:00 UTC, does not evening transition correctly. estimates MWR also be reliable situations but often inaccurate under conditions when, comparison heights, they much deeper. errors originate limitations manufacturer's algorithm misidentification type A climatology annual diurnal cycle height, based data, stability, eddy covariance was created. shallowest (353 m) monthly occurs February deepest (576 June. In winter there no height; BLs rare, yet so BLs. occur night spring summer, common warm season. Finally, gridded we determined observed representative land areas central Finland. spatial variability largest during daytime reducing area over observations would representative.