Decay of the convective boundary layer CBL Decay

Decay of the convective boundary layer (CBL) Decay of the CBL sets in when turbulence aloft cannot be maintained against viscous dissipation due to rapidly decrease in surface buoyancy flux after sunset. Nocturnal boundary layer

Nocturnal jet: Nocturnal jet forms at night-time overland under clear sky conditions. The wind speed may be significantly super-geostrophic.

Inertial oscillation theory Governing equations Assuming Further assuming daytime boundary layer is in a steady state After sunset, nocturnal boundary layer forms, the air above the NBL can be assumed to be free atmosphere, the governing equation becomes

It has a solution in the format of Initial condition Inertial oscillation with period

Example: 0 1 2 3 4 5 6 7 8 9 10 -3. 00 -1. 75 -0. 28 1. 23 2. 58 3. 60 4. 16 4. 19 3. 67 2. 69 1. 36 3. 00 3. 86 4. 23 4. 06 3. 37 2. 34 0. 83 -0. 69 -2. 12 -3. 28 -4. 02 11 12 13 14 15 16 17 18 -0. 14 -1. 62 -2. 90 -3. 81 -4. 22 -4. 10 -3. 45 -3. 00 -4. 24 -3. 93 -3. 10 -1. 88 -0. 41 1. 10 2. 47 3. 00 1 2 3 0 4 5 6 15 7 14 8 9 13 12 11 10

Influence of slope Net force in the vertical: Induced acceleration: Stable condition z

Governing equations in horizontal homogeneous conditions Assuming cooling rate, velocity change rate, and geostrophic wind are constant Introducing nondimensional variables:

Boundary condition: The equation has a solution only if 1 1 0 0