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- Author or Editor: Stacey Heikkinen x
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Abstract
The effect of variations in surface parameters on 24-hour limited area forecasts has been examined on a day in July 1981. The vehicle for the study is a ten-level primitive equation model covering most of the continental United States. Variations in moisture availability, surface roughness and soil flux treatment generally do not produce large differences in 24-hour forecasts of primary variables, except in the extreme cases. Precipitation totals, however, are surprisingly sensitive to the surface treatment in several areas where significant amounts of precipitation are evidenced in a control forecast. In these areas, modulations of 10–30% of the control amount due to surface changes are common. In the areas exhibiting principally large-scale precipitation, evidence points to modulations in evaporation as the cause for the precipitation differences. Areas of principally convective precipitation exhibit differences which can be attributed to model-calculated changes in low-level moisture convergence patterns between forecasts.
Diurnal surface temperature range measured by the VAS instrument on GOUES-3 is compared to those generated in model experiments over the model grid. Good agreement is found in arm with moderate to large moisture availability and roughness heights. Poor agreement is evidenced in the western United States where the daytime surface temperature and flux balance is shown to be critically sensitive to small errors in the moisture availability.
Abstract
The effect of variations in surface parameters on 24-hour limited area forecasts has been examined on a day in July 1981. The vehicle for the study is a ten-level primitive equation model covering most of the continental United States. Variations in moisture availability, surface roughness and soil flux treatment generally do not produce large differences in 24-hour forecasts of primary variables, except in the extreme cases. Precipitation totals, however, are surprisingly sensitive to the surface treatment in several areas where significant amounts of precipitation are evidenced in a control forecast. In these areas, modulations of 10–30% of the control amount due to surface changes are common. In the areas exhibiting principally large-scale precipitation, evidence points to modulations in evaporation as the cause for the precipitation differences. Areas of principally convective precipitation exhibit differences which can be attributed to model-calculated changes in low-level moisture convergence patterns between forecasts.
Diurnal surface temperature range measured by the VAS instrument on GOUES-3 is compared to those generated in model experiments over the model grid. Good agreement is found in arm with moderate to large moisture availability and roughness heights. Poor agreement is evidenced in the western United States where the daytime surface temperature and flux balance is shown to be critically sensitive to small errors in the moisture availability.
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.
Abstract
A cyclone that developed explosively during Intensive Observation Period (IOP) 9 of the Genesis of Atlantic Lows Experiment (GALE) is studied. Detailed surface analysis is conducted based on operationally available data, late reporting ship observations and GALE special observations to determine the surface storm track and deepening rate. GALE dropsonde and rawinsonde data are used to supplement the normal upper-level database, and are analyzed by a research version of the Navy Operational Regional Analysis and Prediction System (NORAPS) using optimal interpolation analysis. These analyses reveal critical subsynoptic features important in the development. Two surface lows are present during the early coastal development period. The western center is coupled to a mobile 500 mb short-wave trough while the eastern center develops in a strong baroclinic zone offshore. The objective analyses also show a strengthening of a jet streak east of the mobile short wave. The divergent quadrant of this jet streak induces upward vertical motion over the eastern of the two coastal low systems.
The rapid development of the eastern center occurs due to the superposition of the upper-level forcing (jet streak) over the low-level perturbation with strong thermal adymion. Dropwindsonde data document the low static stability in the region. NORAPS operational and GALE data forecasts from 1200 UTC 24 February erroneously deepen the western center and result in track errors of 300 to 600 km. The GALE forecast from 0000 UTC 25 February deepens the correct center and makes the best track forecast. All forecasts fail to predict the full extent of the rapid development of this cyclone.
Abstract
A cyclone that developed explosively during Intensive Observation Period (IOP) 9 of the Genesis of Atlantic Lows Experiment (GALE) is studied. Detailed surface analysis is conducted based on operationally available data, late reporting ship observations and GALE special observations to determine the surface storm track and deepening rate. GALE dropsonde and rawinsonde data are used to supplement the normal upper-level database, and are analyzed by a research version of the Navy Operational Regional Analysis and Prediction System (NORAPS) using optimal interpolation analysis. These analyses reveal critical subsynoptic features important in the development. Two surface lows are present during the early coastal development period. The western center is coupled to a mobile 500 mb short-wave trough while the eastern center develops in a strong baroclinic zone offshore. The objective analyses also show a strengthening of a jet streak east of the mobile short wave. The divergent quadrant of this jet streak induces upward vertical motion over the eastern of the two coastal low systems.
The rapid development of the eastern center occurs due to the superposition of the upper-level forcing (jet streak) over the low-level perturbation with strong thermal adymion. Dropwindsonde data document the low static stability in the region. NORAPS operational and GALE data forecasts from 1200 UTC 24 February erroneously deepen the western center and result in track errors of 300 to 600 km. The GALE forecast from 0000 UTC 25 February deepens the correct center and makes the best track forecast. All forecasts fail to predict the full extent of the rapid development of this cyclone.
Abstract
A cyclone that developed explosively during Intensive Observation Period (IOP) 9 of the Genesis of Atlantic Lows Experiment (GALE) is studied. Detailed surface analysis is conducted based on operationally available data, late reporting ship observations and GALE special observations to determine the surface storm track and deepening rate. GALE dropsonde and rawinsonde data are used to supplement the normal upper-level database, and are analyzed by a research version of the Navy Operational Regional Analysis and Prediction System (NORAPS) using optimal interpolation analysis. These analyses reveal critical subsynoptic features important in the development. Two surface lows are present during the early coastal development period. The western center is coupled to a mobile 500 mb short-wave trough while the eastern center develops in a strong baroclinic zone offshore. The objective analyses also show a strengthening of a jet streak east of the mobile short wave. The divergent quadrant of this jet streak induces upward vertical motion over the eastern of the two coastal low systems.
The rapid development of the eastern center occurs due to the superposition of the upper-level forcing (jet streak) over the low-level perturbation with strong thermal adymion. Dropwindsonde data document the low static stability in the region. NORAPS operational and GALE data forecasts from 1200 UTC 24 February erroneously deepen the western center and result in track errors of 300 to 600 km. The GALE forecast from 0000 UTC 25 February deepens the correct center and makes the best track forecast. All forecasts fail to predict the full extent of the rapid development of this cyclone.
Abstract
A cyclone that developed explosively during Intensive Observation Period (IOP) 9 of the Genesis of Atlantic Lows Experiment (GALE) is studied. Detailed surface analysis is conducted based on operationally available data, late reporting ship observations and GALE special observations to determine the surface storm track and deepening rate. GALE dropsonde and rawinsonde data are used to supplement the normal upper-level database, and are analyzed by a research version of the Navy Operational Regional Analysis and Prediction System (NORAPS) using optimal interpolation analysis. These analyses reveal critical subsynoptic features important in the development. Two surface lows are present during the early coastal development period. The western center is coupled to a mobile 500 mb short-wave trough while the eastern center develops in a strong baroclinic zone offshore. The objective analyses also show a strengthening of a jet streak east of the mobile short wave. The divergent quadrant of this jet streak induces upward vertical motion over the eastern of the two coastal low systems.
The rapid development of the eastern center occurs due to the superposition of the upper-level forcing (jet streak) over the low-level perturbation with strong thermal adymion. Dropwindsonde data document the low static stability in the region. NORAPS operational and GALE data forecasts from 1200 UTC 24 February erroneously deepen the western center and result in track errors of 300 to 600 km. The GALE forecast from 0000 UTC 25 February deepens the correct center and makes the best track forecast. All forecasts fail to predict the full extent of the rapid development of this cyclone.
