Abstract:

Based on 43 years’ data of twice-daily radiosonde observations, this study investigated the temporal
variability of the planetary boundary layer height (PBLH) at Jan Mayen, Norway, based on the Bulk
Richardson Number method. It was found that the PBLH during daytime was higher than at night for most
months. In addition, the monthly averaged PBLH in summer (around 262 m) was found much lower than in
spring or winter (about 600 m). The PBLH variations showed good anticorrelation with surface relative humidity.
Because of the influence of the Gulf Stream, the annual temperature difference at the Jan Mayen station
is quite small and the surface temperature shows little seasonal variation. Surface relative humidity exhibits
considerable seasonal variation, with a maximum value in summer and a minimum value in winter.
The higher humidity in summer causes higher latent heat flux that restrains the convective process in the
boundary layer, which leads to the lower summer PBLH. The long-term changes in PBLH at the studied station
also revealed some interesting results. The annual mean PBLH decreased from 1973 to 1988, increased
rapidly between 1988 and 1995, and then fluctuated between 500 and 600 m after 1995.

Key words: Planetary boundary layer height, Jan Mayen, Bulk Richardson Number