Bulk Richardson number and the exchange coefficient at the surface

Figure 3g shows the differences in the momentum exchange coefficient between the perturbed and the control simulations over glaciers and over the transition zone in the Bernese Alps on February 27, 1990. The bulk Richardson number is negative but close to zero in both simulations, but in the perturbed simulation, its value increases slightly during the day and decreases slightly during the night, resulting in a modest increase of its value over glaciers (ARig = 0.002), the daily average being a small decrease over the transition zone The daily average exchange coefficient also decreased over glaciers from 0.006 in the control simulation on average to 0.003 in the perturbed simulation, and from 0.005 to 0.001 over the transition zone, the drop being generally more pronounced during the day, i.e., from 0700 to 1900 UTC.

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