Numerical Studies of Cyclogenesis Events during the Second Intensive Observation Period (IOP-2) of GALE

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  • 1 Department of Meteorology, Naval Postgraduate School, Monterey, California
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Abstract

A research version of the Navy Operational Regional Atmospheric Prediction System (NORAPS) is used to study cyclogenesis events during the second Intensive Observation Period of the Genesis of Atlantic Lows Experiment (GALE). From 1200 UTC 26 January to 0000 UTC 29 January 1986, two cyclogeneses occurred over the East Coast of the United States. NORAPS analyses reveal that the first cyclone develops rapidly due to the superposition of upper-level jet streak forcing over a shallow surface system associated with a well-developed coastal front. Large latent heat release around the cyclone center is considered to be a contributing factor for the rapid deepening of the first cyclone between 0000UTC and 1200 UTC 27 January. Small static stability at low levels coupled with a new upper-level trough-jet system is considered to be an important factor for the formation of the secondary cyclone off the East Coast at 1800 UTC 27 January.

NORAPS predicted the two cyclogenesis events fairly well up to 0000 UTC 28 January. A prediction of too early and too weak of a cold surge is believed to be the main reason for poor forecasts during later periods.

Extra data available from GALE sounding and surface data tapes are added to the operationally received dataset to study the impact of those extra data on analyzing and predicting the two cyclogenesis events. The GALE data impact investigated in this study is concentrated in the increase of spatial resolution, but not temporal resolution, by GALE networks and dropwindsondes. Because the two cyclogenesis events were over land of close to the coast, the regular operational data coverage over the East Coast of the United States was sufficient for the NORAPAS Optimum Interpolation (OI)_ analysis to analyze the important features for the cyclone developments. As a result, the enhancement of data spatial resolution from GALE soundings and surface reports made only limited improvement on NORAPS analyses and forecasts of these two cyclogenesis cases.

Abstract

A research version of the Navy Operational Regional Atmospheric Prediction System (NORAPS) is used to study cyclogenesis events during the second Intensive Observation Period of the Genesis of Atlantic Lows Experiment (GALE). From 1200 UTC 26 January to 0000 UTC 29 January 1986, two cyclogeneses occurred over the East Coast of the United States. NORAPS analyses reveal that the first cyclone develops rapidly due to the superposition of upper-level jet streak forcing over a shallow surface system associated with a well-developed coastal front. Large latent heat release around the cyclone center is considered to be a contributing factor for the rapid deepening of the first cyclone between 0000UTC and 1200 UTC 27 January. Small static stability at low levels coupled with a new upper-level trough-jet system is considered to be an important factor for the formation of the secondary cyclone off the East Coast at 1800 UTC 27 January.

NORAPS predicted the two cyclogenesis events fairly well up to 0000 UTC 28 January. A prediction of too early and too weak of a cold surge is believed to be the main reason for poor forecasts during later periods.

Extra data available from GALE sounding and surface data tapes are added to the operationally received dataset to study the impact of those extra data on analyzing and predicting the two cyclogenesis events. The GALE data impact investigated in this study is concentrated in the increase of spatial resolution, but not temporal resolution, by GALE networks and dropwindsondes. Because the two cyclogenesis events were over land of close to the coast, the regular operational data coverage over the East Coast of the United States was sufficient for the NORAPAS Optimum Interpolation (OI)_ analysis to analyze the important features for the cyclone developments. As a result, the enhancement of data spatial resolution from GALE soundings and surface reports made only limited improvement on NORAPS analyses and forecasts of these two cyclogenesis cases.

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