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Re: Near-adiabatic saturated layers

Posted By: John Brown
Date: 11-December-06 2107Z

In Response To: Near-adiabatic saturated layers (Scott Dennstaedt)

Yes, we occasionally see these features [when the lapse rate is absolutely unstable, they are sometimes referred to as MAULs, or Moist Absolutely Unstable Layers, see "Moist Absolute Instability: The Sixth Static Stability State" George H. Bryan and Michael J. Fritsch
Bulletin of the American Meteorological Society Volume 81, Issue 6 (June 2000) pp. 12071230] in both analyses and forecasts. In the instance you showed, a 14Z analysis, I suspect that this may have been produced by the analysis. The hydrometeor portion of the RUC analysis, which makes use of satellite IR cloud-top information, ceiling, visibility and present weather from METAR obs, as well as GPS precipitable water, can introduce saturation into the analysis if it is not a convective situation. Because this situation is so strongly capped above 850mb, it would not have been considered convective, even though there was a steep lapse rate below the deep capping stable layer. Under these circumstances, if the 14Z METAR was reporting RN, and a low ceiling, then this sounding structure could well have resulted.

As you point out, forecasts can also show these; there is no mechanism in the model to automatically remove them. When these are seen in a forecast it is a sign that vertical motion in the forecast has been strong, and occurring in a convectively unstable environment. The convective parameterization, if activated, will tend to prevent such layers from forming. In a case such as you referenced, explicit grid-scale overturning may have developed on small-scales during the early stages of the forecast. The mixing and precipitation resulting from this would eventually remove the saturation.

Messages In This Thread

Near-adiabatic saturated layers -- Scott Dennstaedt -- 10-December-06 1552Z
Re: Near-adiabatic saturated layers -- John Brown -- 11-December-06 2107Z
Re: Near-adiabatic saturated layers -- Scott Dennstaedt -- 14-December-06 0438Z
Re: Near-adiabatic saturated layers -- richard mamrosh -- 14-December-06 1448Z
Re: Near-adiabatic saturated layers -- Lyle Alexander -- 15-December-06 1605Z

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