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Abstract
The Nimbus-7 Total Ozone Mapping spectrometer (TOMS) was used to map the distribution of total Ozone in and around western Atlantic tropical cyclones from 1979 to 1982. It was found that the TOMS-observed total Ozone distribution within the subtropics during the tropical cyclone seasonal correlated well with the tropopause topoghraphy, similar to earlier middle-latitudinal observations. This relationship made it possible to use TOMS to monitor the propagation of upper-tropospheric subtropical transient waves and the mutual adjustment between the tropical cyclone and the upper-tropospheric waves during their interaction. These total ozone patterns reflected the three-dimensional upper-tropospheric transport processes that were conducive for storm intensification and weakening. It was also found from satellite observations and numerical model simulations that modification of the environmental distribution of total ozone by the tropical cyclones was primarily caused by the secondary circulation associated with the tropical cyclone's outflow jet and the intrusion of stratospheric air in the eyes of tropical cyclones.
Abstract
The Nimbus-7 Total Ozone Mapping spectrometer (TOMS) was used to map the distribution of total Ozone in and around western Atlantic tropical cyclones from 1979 to 1982. It was found that the TOMS-observed total Ozone distribution within the subtropics during the tropical cyclone seasonal correlated well with the tropopause topoghraphy, similar to earlier middle-latitudinal observations. This relationship made it possible to use TOMS to monitor the propagation of upper-tropospheric subtropical transient waves and the mutual adjustment between the tropical cyclone and the upper-tropospheric waves during their interaction. These total ozone patterns reflected the three-dimensional upper-tropospheric transport processes that were conducive for storm intensification and weakening. It was also found from satellite observations and numerical model simulations that modification of the environmental distribution of total ozone by the tropical cyclones was primarily caused by the secondary circulation associated with the tropical cyclone's outflow jet and the intrusion of stratospheric air in the eyes of tropical cyclones.
Abstract
During the passage of hurricane Frederic in 1979, four ocean current meter arrays in water depths of 100–950 m detected both a baroclinic and a depth-independent response in the near-inertial frequency band. Although the oceanic response was predominately baroclinic, the hurricane excited a depth-independent component of 5–11 cm s−1.
The origin and role of the depth-independent component of velocity is investigated using a linear analytical model and numerical simulations from a 17-level primitive equation model with a free surface. Both models are forced with an idealized wind stress pattern based on the observed storm parameters in hurricane Frederic. In an analytical model, the Green's function (K 0) is convolved with the wind stress curl to predict a sea surface depression of approximately 20 cm from the equilibrium position. The near-inertial velocities are simulated by convolving the slope of the sea surface depression with a second Green's function. The barotropic current velocities rotate inertially with periods shifted above the local inertial period by 1%–2% and the maximum amplitude of 11 cm s−1 is displaced to the right of the track at x = 2R max (radius of maximum winds).
The free surface depression simulated by the primitive-equation model is also about 18–20 cm. The primitive equation model simulations indicate that the vertical mean pressure gradient excites 10–11 cm s−1 depth-averaged currents at x = 3R max. The net divergence and convergence of the horizontal velocities induces vertical deflections of the sea surface. The spatial pattern of the barotropic amplitudes simulated by the numerical and analytical models differ by less than 2 cm s−1 in the region 0 < x < 4R max, which suggests that the barotropic response to the passage of a moving hurricane is governed by linear processes.
Abstract
During the passage of hurricane Frederic in 1979, four ocean current meter arrays in water depths of 100–950 m detected both a baroclinic and a depth-independent response in the near-inertial frequency band. Although the oceanic response was predominately baroclinic, the hurricane excited a depth-independent component of 5–11 cm s−1.
The origin and role of the depth-independent component of velocity is investigated using a linear analytical model and numerical simulations from a 17-level primitive equation model with a free surface. Both models are forced with an idealized wind stress pattern based on the observed storm parameters in hurricane Frederic. In an analytical model, the Green's function (K 0) is convolved with the wind stress curl to predict a sea surface depression of approximately 20 cm from the equilibrium position. The near-inertial velocities are simulated by convolving the slope of the sea surface depression with a second Green's function. The barotropic current velocities rotate inertially with periods shifted above the local inertial period by 1%–2% and the maximum amplitude of 11 cm s−1 is displaced to the right of the track at x = 2R max (radius of maximum winds).
The free surface depression simulated by the primitive-equation model is also about 18–20 cm. The primitive equation model simulations indicate that the vertical mean pressure gradient excites 10–11 cm s−1 depth-averaged currents at x = 3R max. The net divergence and convergence of the horizontal velocities induces vertical deflections of the sea surface. The spatial pattern of the barotropic amplitudes simulated by the numerical and analytical models differ by less than 2 cm s−1 in the region 0 < x < 4R max, which suggests that the barotropic response to the passage of a moving hurricane is governed by linear processes.
Abstract
Special Sensor Microwave/Imager (SSM/I) observations were used to examine the spatial and temporal changes of the precipitation characteristics of tropical cyclones. SSM/I observations were also combined with the results of a tropical cyclone numerical model to examine the role of inner-core diabatic heating in subsequent intensity changes of tropical cyclones. Included in the SSM/I observations were rainfall characteristics of 18 named western North Atlantic tropical cyclones between 1987 and 1989. The SSM/I rain-rate algorithm that employed the 85-GHz channel provided an analysis of the rain-rate distribution in greater detail. However, the SSM/I algorithm underestimated the rain rates when compared to in situ techniques but appeared to be comparable to the rain rates obtained from other satellite-borne passive microwave radiometers.
The analysis of SSM/I observations found that more intense systems had higher rain rates, more latent heat release, and a greater contribution from heavier rain to the total tropical cyclone rainfall. In addition, regions with the heaviest rain rates were found near the center of the most intense tropical cyclones. Observational analysis from SSM/I also revealed that the greatest rain rates in the inner-core regions were found in the right half of fast-moving tropical cyclones, while the heaviest rain rates in slow-moving tropical cyclones were found in the forward half. The combination of SSM/I observations and an interpretation of numerical model simulations revealed that the correlation between changes in the inner core diabatic beating and the subsequent intensity become greater as the tropical cyclones became more intense.
Abstract
Special Sensor Microwave/Imager (SSM/I) observations were used to examine the spatial and temporal changes of the precipitation characteristics of tropical cyclones. SSM/I observations were also combined with the results of a tropical cyclone numerical model to examine the role of inner-core diabatic heating in subsequent intensity changes of tropical cyclones. Included in the SSM/I observations were rainfall characteristics of 18 named western North Atlantic tropical cyclones between 1987 and 1989. The SSM/I rain-rate algorithm that employed the 85-GHz channel provided an analysis of the rain-rate distribution in greater detail. However, the SSM/I algorithm underestimated the rain rates when compared to in situ techniques but appeared to be comparable to the rain rates obtained from other satellite-borne passive microwave radiometers.
The analysis of SSM/I observations found that more intense systems had higher rain rates, more latent heat release, and a greater contribution from heavier rain to the total tropical cyclone rainfall. In addition, regions with the heaviest rain rates were found near the center of the most intense tropical cyclones. Observational analysis from SSM/I also revealed that the greatest rain rates in the inner-core regions were found in the right half of fast-moving tropical cyclones, while the heaviest rain rates in slow-moving tropical cyclones were found in the forward half. The combination of SSM/I observations and an interpretation of numerical model simulations revealed that the correlation between changes in the inner core diabatic beating and the subsequent intensity become greater as the tropical cyclones became more intense.
Abstract
In an effort to improve the tropical cyclone track forecast, two preprocessing procedures are applied to an operational baroclinic forecast system at the Central Weather Bureau (CWB) in Taipei. The first replaces the environmental wind field near the storm by the previous 6-h.movement vector of the storm. The second incorporates a wavenumber-1 asymmetry constructed by matching the flow at the center of the asymmetry with the previous 6-h storm movement. Applying both processes to the 32 typhoon casts archived at the CWB in 1990 reduces the averaged 48-h forecast distance error from 474 to 351 km.
Multiexisting typhoons may have interactions among themselves that depend on relative intensity. Proper representation of the intensities in the initial bogus is important for the track forecast. Experiments with different initial bogus intensities are conducted on a case of dual typhoons-Nat and Mireille in 1991. The forecast using different bogus vortices according to the estimated intensities of each typhoon gives substantially smaller errors than that using identical bogus vortices. The impact of initial bogus vortex intensity on the track forecast for single typhoon cases is also illustrated.
Abstract
In an effort to improve the tropical cyclone track forecast, two preprocessing procedures are applied to an operational baroclinic forecast system at the Central Weather Bureau (CWB) in Taipei. The first replaces the environmental wind field near the storm by the previous 6-h.movement vector of the storm. The second incorporates a wavenumber-1 asymmetry constructed by matching the flow at the center of the asymmetry with the previous 6-h storm movement. Applying both processes to the 32 typhoon casts archived at the CWB in 1990 reduces the averaged 48-h forecast distance error from 474 to 351 km.
Multiexisting typhoons may have interactions among themselves that depend on relative intensity. Proper representation of the intensities in the initial bogus is important for the track forecast. Experiments with different initial bogus intensities are conducted on a case of dual typhoons-Nat and Mireille in 1991. The forecast using different bogus vortices according to the estimated intensities of each typhoon gives substantially smaller errors than that using identical bogus vortices. The impact of initial bogus vortex intensity on the track forecast for single typhoon cases is also illustrated.
This report discusses the design and implementation of a specialized forecasting system that was set up to support the observational component of the Labrador Sea Deep Convection Experiment. This ongoing experiment is a multidisciplinary program of observations, theory, and modeling aimed at improving our knowledge of the deep convection process in the ocean, and the air–sea interaction that forces it. The observational part of the program was centered around a cruise of the R/V Knorr during winter 1997, as well as several complementary meteorological research flights. To aid the planning of ship and aircraft operations a specially tailored mesoscale model was run over the Labrador Sea, with the model output postprocessed and transferred to a remote field base. The benefits of using a warm-start analysis cycle in the model are discussed. The utility of the forecasting system is illustrated through a description of the flight planning process for several cases. The forecasts proved to be invaluable both in ship operations and in putting the aircraft in the right place at the right time. In writing this narrative the authors hope to encourage the use of similar forecasting systems in the support of future field programs, something that is becoming increasingly possible with the rise in real-time numerical weather prediction.
This report discusses the design and implementation of a specialized forecasting system that was set up to support the observational component of the Labrador Sea Deep Convection Experiment. This ongoing experiment is a multidisciplinary program of observations, theory, and modeling aimed at improving our knowledge of the deep convection process in the ocean, and the air–sea interaction that forces it. The observational part of the program was centered around a cruise of the R/V Knorr during winter 1997, as well as several complementary meteorological research flights. To aid the planning of ship and aircraft operations a specially tailored mesoscale model was run over the Labrador Sea, with the model output postprocessed and transferred to a remote field base. The benefits of using a warm-start analysis cycle in the model are discussed. The utility of the forecasting system is illustrated through a description of the flight planning process for several cases. The forecasts proved to be invaluable both in ship operations and in putting the aircraft in the right place at the right time. In writing this narrative the authors hope to encourage the use of similar forecasting systems in the support of future field programs, something that is becoming increasingly possible with the rise in real-time numerical weather prediction.
Abstract
The mutual adjustment between upper-tropospheric troughs and the structure of western Atlantic Tropical Cyclones Florence (1988) and Irene (1981) are analyzed using satellite and in situ data. Satellite-observed tracers (e.g., cirrus clouds, water vapor, and ozone) art used to monitor the circulation within the tropical cyclones' environment. The tropical cyclones' convection is inferred from satellite flown passive microwave and infrared sensors. In addition, numerical model simulations are used to analyze and interpret these satellite observations. The study suggests that the initiation and maintenance of intense convective outbreaks in these tropical cyclones during their mature stage are related to the channeling and strengthening of their outflow by upper-tropospheric troughs. The convection can be enhanced in response to the outflow jet-induced import of eddy relative angular momentum and ascending motion associated with the thermally direct circulation. The channeling and strengthening of the outflow occurs when the upper-tropospheric troughs are located in a favorable position relative to the tropical cyclones. Both Florence and Irene intensify after the onset of these intense convective episodes. Satellite observations also suggest that the cessation in the convection of the two tropical cyclones occurs when the upper-tropospheric troughs move near or over the tropical cyclones, resulting in the weakening of their outflow and the entrainment of dry upper-tropospheric air into their inner core.
Abstract
The mutual adjustment between upper-tropospheric troughs and the structure of western Atlantic Tropical Cyclones Florence (1988) and Irene (1981) are analyzed using satellite and in situ data. Satellite-observed tracers (e.g., cirrus clouds, water vapor, and ozone) art used to monitor the circulation within the tropical cyclones' environment. The tropical cyclones' convection is inferred from satellite flown passive microwave and infrared sensors. In addition, numerical model simulations are used to analyze and interpret these satellite observations. The study suggests that the initiation and maintenance of intense convective outbreaks in these tropical cyclones during their mature stage are related to the channeling and strengthening of their outflow by upper-tropospheric troughs. The convection can be enhanced in response to the outflow jet-induced import of eddy relative angular momentum and ascending motion associated with the thermally direct circulation. The channeling and strengthening of the outflow occurs when the upper-tropospheric troughs are located in a favorable position relative to the tropical cyclones. Both Florence and Irene intensify after the onset of these intense convective episodes. Satellite observations also suggest that the cessation in the convection of the two tropical cyclones occurs when the upper-tropospheric troughs move near or over the tropical cyclones, resulting in the weakening of their outflow and the entrainment of dry upper-tropospheric air into their inner core.
Abstract
Hurricane Opal (1995) experienced a rapid, unexpected intensification in the Gulf of Mexico that coincided with its encounter with a warm core ring (WCR). The relative positions of Opal and the WCR and the timing of the intensification indicate strong air–sea interactions between the tropical cyclone and the ocean. To study the mutual response of Opal and the Gulf of Mexico, a coupled model is used consisting of a nonhydrostatic atmospheric component of the Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS), and the hydrostatic Geophysical Fluid Dynamics Laboratory’s Modular Ocean Model version 2 (MOM 2).
The coupling between the ocean and the atmosphere components of the model are accomplished by conservation of heat, salt, momentum, as well as the sensible and latent heat fluxes at the air–sea interface. The atmospheric model has two nests with spatial resolutions of 0.6° and 0.2°. The ocean model has a uniform resolution of 0.2°. The oceanic model domain covers the Gulf of Mexico basin and coincides with a fine-mesh atmospheric domain of the COAMPS. The initial condition for the atmospheric component of COAMPS is the archived Navy Operational Global Atmospheric Prediction System operational global analysis, enhanced with observations. The initial ocean condition for the oceanic component is obtained from a 2-yr MOM 2 simulation with climatological forcing and fixed mass inflow into the Gulf. The initial state in the Gulf of Mexico consists of a realistic Loop Current and a shed WCR.
The 72-h simulation of the coupled system starting from 1200 UTC 2 October 1995 reproduces the observed storm intensity with a minimum sea level pressure (MSLP) of 918 hPa, occurring at 1800 UTC 4 October, a 6-h delay compared to the observation. The rapid intensification to the maximum intensity and the subsequent weakening are not as dramatic as the observed. The simulated track is located slightly to the east of the observed track, placing it directly over the simulated WCR, where the sea surface temperature (SST) cooling is approximately 0.5°C, consistent with buoy measurements acquired within the WCR. This cooling is significantly less over the WCR than over the common Gulf water due to the deeper and warmer layers in the WCR. Wind-induced currents of 150 cm s−1 are similar to those in earlier idealized simulations, and the forced current field in Opal’s wake is characterized by near-inertial oscillations superimposed on the anticyclonic circulation around the WCR.
Several numerical experiments are conducted to isolate the effects of the WCR and the ocean–atmosphere coupling. The major findings of these numerical experiments are summarized as follows.
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Opal intensifies an additional 17 hPa between the times when Opal’s center enters and exits the outer edge of the WCR. Without the WCR, Opal only intensifies another 7 hPa in the same period.
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The maximum surface sensible and latent heat flux amounts to 2842 W m−2. This occurs when Opal’s surface circulation brings northwesterly flow over the SST gradient in the northwestern quadrant of the WCR.
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Opal extracts 40% of the available heat capacity (temperature greater than 26°C) from the WCR.
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While the WCR enhances the tropical cyclone and ocean coupling as indicated by strong interfacial fluxes, it reduces the negative feedback. The negative feedback of the induced SST cooling to Hurricane Opal is 5 hPa. This small feedback is due to the relatively large heat content of the WCR, and the negative feedback is stronger in the absence of the WCR, producing a difference of 8 hPa in the MSLP of Opal.
Abstract
Hurricane Opal (1995) experienced a rapid, unexpected intensification in the Gulf of Mexico that coincided with its encounter with a warm core ring (WCR). The relative positions of Opal and the WCR and the timing of the intensification indicate strong air–sea interactions between the tropical cyclone and the ocean. To study the mutual response of Opal and the Gulf of Mexico, a coupled model is used consisting of a nonhydrostatic atmospheric component of the Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS), and the hydrostatic Geophysical Fluid Dynamics Laboratory’s Modular Ocean Model version 2 (MOM 2).
The coupling between the ocean and the atmosphere components of the model are accomplished by conservation of heat, salt, momentum, as well as the sensible and latent heat fluxes at the air–sea interface. The atmospheric model has two nests with spatial resolutions of 0.6° and 0.2°. The ocean model has a uniform resolution of 0.2°. The oceanic model domain covers the Gulf of Mexico basin and coincides with a fine-mesh atmospheric domain of the COAMPS. The initial condition for the atmospheric component of COAMPS is the archived Navy Operational Global Atmospheric Prediction System operational global analysis, enhanced with observations. The initial ocean condition for the oceanic component is obtained from a 2-yr MOM 2 simulation with climatological forcing and fixed mass inflow into the Gulf. The initial state in the Gulf of Mexico consists of a realistic Loop Current and a shed WCR.
The 72-h simulation of the coupled system starting from 1200 UTC 2 October 1995 reproduces the observed storm intensity with a minimum sea level pressure (MSLP) of 918 hPa, occurring at 1800 UTC 4 October, a 6-h delay compared to the observation. The rapid intensification to the maximum intensity and the subsequent weakening are not as dramatic as the observed. The simulated track is located slightly to the east of the observed track, placing it directly over the simulated WCR, where the sea surface temperature (SST) cooling is approximately 0.5°C, consistent with buoy measurements acquired within the WCR. This cooling is significantly less over the WCR than over the common Gulf water due to the deeper and warmer layers in the WCR. Wind-induced currents of 150 cm s−1 are similar to those in earlier idealized simulations, and the forced current field in Opal’s wake is characterized by near-inertial oscillations superimposed on the anticyclonic circulation around the WCR.
Several numerical experiments are conducted to isolate the effects of the WCR and the ocean–atmosphere coupling. The major findings of these numerical experiments are summarized as follows.
-
Opal intensifies an additional 17 hPa between the times when Opal’s center enters and exits the outer edge of the WCR. Without the WCR, Opal only intensifies another 7 hPa in the same period.
-
The maximum surface sensible and latent heat flux amounts to 2842 W m−2. This occurs when Opal’s surface circulation brings northwesterly flow over the SST gradient in the northwestern quadrant of the WCR.
-
Opal extracts 40% of the available heat capacity (temperature greater than 26°C) from the WCR.
-
While the WCR enhances the tropical cyclone and ocean coupling as indicated by strong interfacial fluxes, it reduces the negative feedback. The negative feedback of the induced SST cooling to Hurricane Opal is 5 hPa. This small feedback is due to the relatively large heat content of the WCR, and the negative feedback is stronger in the absence of the WCR, producing a difference of 8 hPa in the MSLP of Opal.
Abstract
Data from the Special Sensor Microwave/Imager (SSM/I) on board a Defense Meteorological Satellite Program satellite are used to study the precipitation patterns and wind fields associated with Hurricane Florence (1988). SSM/I estimates indicate that the intensification of Florence was coincident with the increase in total latent beat release. Additionally, an increase in the concentration and areal coverage of heavier rain rates near the center is observed. SSM/I marine surface winds of Florence are examined and compared to in situ data, and to an enhanced objective isotach analysis over the Gulf of Mexico. Results indicate that the SSM/I winds are weaker than those depicted in the enhanced objective analysis and slightly stronger than in situ observations. Finally, center positions of Florence are estimated using the 85-GHz brightness temperature imagery. Much improved estimates are achieved using this imagery compared to using GOES infrared imagery. These results concur with previous studies that applications of SSM/I data could be valuable in augmenting current methods of tropical cyclone analysis.
Abstract
Data from the Special Sensor Microwave/Imager (SSM/I) on board a Defense Meteorological Satellite Program satellite are used to study the precipitation patterns and wind fields associated with Hurricane Florence (1988). SSM/I estimates indicate that the intensification of Florence was coincident with the increase in total latent beat release. Additionally, an increase in the concentration and areal coverage of heavier rain rates near the center is observed. SSM/I marine surface winds of Florence are examined and compared to in situ data, and to an enhanced objective isotach analysis over the Gulf of Mexico. Results indicate that the SSM/I winds are weaker than those depicted in the enhanced objective analysis and slightly stronger than in situ observations. Finally, center positions of Florence are estimated using the 85-GHz brightness temperature imagery. Much improved estimates are achieved using this imagery compared to using GOES infrared imagery. These results concur with previous studies that applications of SSM/I data could be valuable in augmenting current methods of tropical cyclone analysis.
Abstract
In support of the Department of Defense's Gulf War Illness study, the Naval Research Laboratory (NRL) has performed global and mesoscale meteorological reanalyses to provide a quantitative atmospheric characterization of the Persian Gulf region during the period between 15 January and 15 March 1991. This paper presents a description of the mid- to late-winter synoptic conditions, mean statistical scores, and near-surface mean conditions of the Gulf War theater drawn from the 2-month reanalysis.
The reanalysis is conducted with the U.S. Navy's operational global and mesoscale analysis and prediction systems: the Navy Operational Global Atmospheric Prediction System (NOGAPS) and the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). The synoptic conditions for the 2-month period can be characterized as fairly typical for the northeast monsoon season, with only one significant precipitation event affecting the Persian Gulf region.
A comparison of error statistics to those from other mesoscale models with similar resolution covering complex terrains (though in different geographic locations) is performed. Results indicate similar if not smaller error statistics for the current study even though this 2-month reanalysis is conducted in an extremely data-sparse area, lending credence to the reanalysis dataset.
The mean near-surface conditions indicate that variability in the wind and temperature fields arises mainly because of the differential diurnal processes in the region characterized by complex surface characteristics and terrain height. The surface wind over lower elevation, interior, land regions is mostly light and variable, especially in the nocturnal surface layer. The strong signature of diurnal variation of sea–land as well as lake–land circulation is apparent, with convergence over the water during the night and divergence during the day. Likewise, the boundary layer is thus strongly modulated by the diurnal cycle near the surface. The low mean PBL height and light mean winds combine to yield very low ventilation efficiency over the Saudi and Iraqi plains.
Abstract
In support of the Department of Defense's Gulf War Illness study, the Naval Research Laboratory (NRL) has performed global and mesoscale meteorological reanalyses to provide a quantitative atmospheric characterization of the Persian Gulf region during the period between 15 January and 15 March 1991. This paper presents a description of the mid- to late-winter synoptic conditions, mean statistical scores, and near-surface mean conditions of the Gulf War theater drawn from the 2-month reanalysis.
The reanalysis is conducted with the U.S. Navy's operational global and mesoscale analysis and prediction systems: the Navy Operational Global Atmospheric Prediction System (NOGAPS) and the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). The synoptic conditions for the 2-month period can be characterized as fairly typical for the northeast monsoon season, with only one significant precipitation event affecting the Persian Gulf region.
A comparison of error statistics to those from other mesoscale models with similar resolution covering complex terrains (though in different geographic locations) is performed. Results indicate similar if not smaller error statistics for the current study even though this 2-month reanalysis is conducted in an extremely data-sparse area, lending credence to the reanalysis dataset.
The mean near-surface conditions indicate that variability in the wind and temperature fields arises mainly because of the differential diurnal processes in the region characterized by complex surface characteristics and terrain height. The surface wind over lower elevation, interior, land regions is mostly light and variable, especially in the nocturnal surface layer. The strong signature of diurnal variation of sea–land as well as lake–land circulation is apparent, with convergence over the water during the night and divergence during the day. Likewise, the boundary layer is thus strongly modulated by the diurnal cycle near the surface. The low mean PBL height and light mean winds combine to yield very low ventilation efficiency over the Saudi and Iraqi plains.
Abstract
Fields of rainfall rates, integrated water vapor (IWV), and marine surface wind speeds retrieved by the Special Sensor Microwave/Imager (SSM/I) during the intensive observational period 4 on 4 January 1989 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) were analyzed. Subjectively analyzed and model-simulated frontal structures were used to examine the spatial relationship of the SSM/I observed fields to the rapidly intensifying storm and the associated fronts. Qualitative and quantitative comparisons of SSM/I retrievals with GOES imagery, conventional observations, and results produced from the Naval Research Laboratory's (NRL) limited-area numerical model were also made.
SSM/I rainfall was found along the cold and warm fronts, with heavy precipitation within frontal bands. The spatial pattern and characteristics of SSM/I precipitation closely resembled those simulated by the model. Both the warm and the cold front were found to be located near the area of the strongest gradient in IWV. In the warm sector, areas of IWV greater than 40 mm were found, an amount supported by model simulations. Both SSM/I rain rate and IWV distribution were found to be useful in locating the cold and warm fronts. There was good agreement on the relationship of frontal locations to the precipitation patterns and IWV gradients. Most of the high-wind area near the storm center was obscured by clouds for marine surface wind retrieval. SSM/I-retrieved marine surface winds outside the cloud shield (flag 0) were compared to ship- and buoy-reported winds. It was found that the retrieved wind estimates were within 0–3 m s−1 of in situ observation over areas of slow wind shifts. The errors became larger in regions of rapid wind shifts.
Abstract
Fields of rainfall rates, integrated water vapor (IWV), and marine surface wind speeds retrieved by the Special Sensor Microwave/Imager (SSM/I) during the intensive observational period 4 on 4 January 1989 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) were analyzed. Subjectively analyzed and model-simulated frontal structures were used to examine the spatial relationship of the SSM/I observed fields to the rapidly intensifying storm and the associated fronts. Qualitative and quantitative comparisons of SSM/I retrievals with GOES imagery, conventional observations, and results produced from the Naval Research Laboratory's (NRL) limited-area numerical model were also made.
SSM/I rainfall was found along the cold and warm fronts, with heavy precipitation within frontal bands. The spatial pattern and characteristics of SSM/I precipitation closely resembled those simulated by the model. Both the warm and the cold front were found to be located near the area of the strongest gradient in IWV. In the warm sector, areas of IWV greater than 40 mm were found, an amount supported by model simulations. Both SSM/I rain rate and IWV distribution were found to be useful in locating the cold and warm fronts. There was good agreement on the relationship of frontal locations to the precipitation patterns and IWV gradients. Most of the high-wind area near the storm center was obscured by clouds for marine surface wind retrieval. SSM/I-retrieved marine surface winds outside the cloud shield (flag 0) were compared to ship- and buoy-reported winds. It was found that the retrieved wind estimates were within 0–3 m s−1 of in situ observation over areas of slow wind shifts. The errors became larger in regions of rapid wind shifts.
