Mesoscale Parallel Experiment Log

Experiment Name

Eta-32 with modified shallow convection parameterzation

Parallel Slot

ETAW

Control Slot

ETAV

Start date of parallel experiment

12Z 2004/06/28

End date of parallel experiment

00Z 2004/09/09

CHANGES

The Eta forecast code has been modified with the following changes to the shallow convection parameterization:

Increased the depth of shallow (nonprecipitating) convection from 200 hPa to 400 hPa while keeping the same lower limit for deep (precipitating) convection at 200 hPa. Currently convection greater (less) than 200 hPa in depth is assumed to be deep (shallow). This change allows convection between 200 hPa and 400 hPa to be deep if it passes the enthalpy adjustment and entropy check, otherwise it is determined if is can support shallow convection.

The cloud-top level is associated with the highest level where the parcel temperature is warmer than the environment. The parcel temperature is calculated assuming a small fraction (5%) of ambient air is mixed at cloud top following the procedure of Betts and Miller (1993). Shallow convection is considered only if the level of free convection (LFC) is within 100 hPa of the lifting condensation level (LCL) of the most unstable parcel. Currently the top of shallow convection is associated with the maximum increase in relative humidity with pressure (similar to where the decrease in relative humidity with height is greatest).

Currently shallow convection is aborted if a number of criteria are not met (see Janjic, 1994), including the creation of supersaturated conditions within a layer. This particular criterion was eliminated, allowing shallow convection to continue to transport heat and moisture between different levels while at the same time also allowing grid-scale condensation to occur. These conditions are consistent with stratocumulus clouds where convective overturning is active within cloud layers.

Experiment changes log

Background links

Evaluation of parallel results

Daily forecast maps

Daily forecast stats

Verification of precipitation and against rawinsondes / surface data

Verification of precipitation and against rawinsondes / surface data (07/01/04-07/21/04)

Conclusion

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