<P> In meteorology the planetary boundary layer ( PBL ) , also known as the atmospheric boundary layer ( ABL ) , is the lowest part of the atmosphere . Its behavior is directly influenced by its contact with a planetary surface . On Earth it usually responds to changes in surface radiative forcing in an hour or less . In this layer physical quantities such as flow velocity , temperature , moisture , etc. , display rapid fluctuations ( turbulence ) and vertical mixing is strong . Above the PBL is the `` free atmosphere '' where the wind is approximately geostrophic ( parallel to the isobars ) while within the PBL the wind is affected by surface drag and turns across the isobars . The free atmosphere is usually nonturbulent , or only intermittently turbulent . </P>
<P> In meteorology the planetary boundary layer ( PBL ) , also known as the atmospheric boundary layer ( ABL ) , is the lowest part of the atmosphere . Its behavior is directly influenced by its contact with a planetary surface . On Earth it usually responds to changes in surface radiative forcing in an hour or less . In this layer physical quantities such as flow velocity , temperature , moisture , etc. , display rapid fluctuations ( turbulence ) and vertical mixing is strong . Above the PBL is the `` free atmosphere '' where the wind is approximately geostrophic ( parallel to the isobars ) while within the PBL the wind is affected by surface drag and turns across the isobars . The free atmosphere is usually nonturbulent , or only intermittently turbulent . </P>
this is the layer in the atmosphere where friction is important in determining wind speed
this is the layer in the atmosphere where friction is important in determining wind speed
planetary boundary layer
planetary boundary layer