An Investigation of the ERICA IOP-2 Cyclone Using the NORAPS Model
Miller, Ronald J.
Wash, Carlyle H.
Nuss, Wendell L.
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Rapid cyclogenesis is studied using the Naval Operational Regional Atmospheric Prediction System (NORAPS) numerical model. The cyclone studied occurred during the second Intensive Observation Period (IOP-2) of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA). Several simulations were run to examine the inability of this and other models to correctly predict development movement, and other characteristics of this cyclone. The experiments consisted of varying the cumulus parameterization and the initial low-level temperature and moisture fields. The exact cumulus specification did not appear to have a significant effect on the forecast sea level pressure. Although convective precipitation amounts varied with different parameterizations, the stable precipitation recovered the difference resulting in a nearly equivalent amount of latent heating. A dry simulation showed that the latent heat released from precipitation is necessary to achieve the observed deepening rate. A poor analysis over the data-sparse ocean and lack of a moisture analysis caused the modeled atmosphere to be too potentially unstable, resulting in much more precipitation and development than was observed early in the forecast period. A simulation using the global analysis fields for initialization, which were somewhat cooler and drier than the NORAPS initial fields, resulted in a better forecast, although the observed deepening rate was not achieved. All simulations incorrectly develop the first of two lows. Numerical models run at the National Meteorological Center (NMC) also failed to correctly deepen the secondary low, and varied greatly in their predicted deepening rates.
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