Flows attached to topographical features and variation of surface conditions (vegetation height and density, soil type and wetness, water surfaces) are sometimes referred to as micrometeorological circulations

a) Cold air drainzage – SUB MENU

With sufficiently weak regional flow, most of the Earth’s surface may at times experience cold air drainage and formation of cold air pools in low lying areas. With weak regional flow, even very weak slopes generate slope flows so that there is only some flow, even if not readily observable by a human without adequate instrumention. Gentle slopes often occur simultaneously on different scales.  Drainage flows from different slopes may interact. The literature concentrates on flows over isolated well-defined slopes.

A larger-scale slope may generate nocturnal downslope flow that appears as a regional flow with respect to local drainage flow down a smaller-scale slope.   On a night with strong surface cooling and weak larger-scale flow, an idealized parcel originating from upland areas may drain into small gullies, which in turn drain into little valleys, which in turn drain into larger valleys, and so on, to the sea.

b)  Cold pools and frost issues – SUB MENU

When local slopes are small, drainage flows may be minimal and the turbulence may be very weak.  This corresponds to weaker downward heat flux and  allows stronger cooling of the air and formation of a cold pool.   link to frost damage***

c) Upslope flows – SUB MENU

Upslope flow of warm air is associated with surface heating and significant turbulent mixing.  This mixing transport stronger momentum downward toward the surface which can eliminate the upslope flow.  link to The Oak Savanna Project **