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Abstract
Airflow through a developing midlatitude disturbance is analyzed in a relative-wind isentropic system in order to provide insight into how the cloud pattern evolves into the familiar comma shape. The model presented makes use of various concepts such as that of the conveyor belt and explores the relationship between the configuration of the major airstreams and such features as the jet streams and the dry tongue. The model also relates vertical motion and precipitation to the origin and vertical displacement of the airstreams and attaches special significance to airstream boundaries, which manifest themselves as sharp discontinuities in cloud and weather patterns.
Abstract
Airflow through a developing midlatitude disturbance is analyzed in a relative-wind isentropic system in order to provide insight into how the cloud pattern evolves into the familiar comma shape. The model presented makes use of various concepts such as that of the conveyor belt and explores the relationship between the configuration of the major airstreams and such features as the jet streams and the dry tongue. The model also relates vertical motion and precipitation to the origin and vertical displacement of the airstreams and attaches special significance to airstream boundaries, which manifest themselves as sharp discontinuities in cloud and weather patterns.
Abstract
An analysis of sea-surface temperatures over the tropical Atlantic for the past 5 yr shows a correlation between the number of tropical storms formed between July 10 and September 20 and the ocean temperatures over a wide area centered near 10°N and 35°W.
Abstract
An analysis of sea-surface temperatures over the tropical Atlantic for the past 5 yr shows a correlation between the number of tropical storms formed between July 10 and September 20 and the ocean temperatures over a wide area centered near 10°N and 35°W.
Abstract
A daily analysis of the 2,000- and 10,000-ft streamlines over West Africa was made for a 3½-mo period beginning in July 1968. With the aid of satellite photographs and auxiliary sea-level pressure data, a total of 33 synoptic scale wave perturbations were observed to move across West Africa and the tropical Atlantic Ocean during this period. Some general features of these disturbances are summarized, including facts on their origin, speed, intensity, distribution of sea-level pressure, appearance on the satellite photographs, and movement over the Atlantic Ocean. The effects of the large-scale circulation and the influence of sea-surface temperatures on the movement and intensity of disturbances are also discussed.
Abstract
A daily analysis of the 2,000- and 10,000-ft streamlines over West Africa was made for a 3½-mo period beginning in July 1968. With the aid of satellite photographs and auxiliary sea-level pressure data, a total of 33 synoptic scale wave perturbations were observed to move across West Africa and the tropical Atlantic Ocean during this period. Some general features of these disturbances are summarized, including facts on their origin, speed, intensity, distribution of sea-level pressure, appearance on the satellite photographs, and movement over the Atlantic Ocean. The effects of the large-scale circulation and the influence of sea-surface temperatures on the movement and intensity of disturbances are also discussed.
Abstract
Surface and upper air (700 mb) analyses along with high-quality satellite photographs are presented for a 2-week period during August and September 1967. These show, in particular, the structure and motion over the continent of Africa of four major wave disturbances, three of which later became Atlantic hurricanes. The evolution of cloudiness and convection and the intensification of the disturbance at low levels over West Africa are examined in detail and related to certain climatological features of the area. Some general characteristics of the disturbances are discussed.
Abstract
Surface and upper air (700 mb) analyses along with high-quality satellite photographs are presented for a 2-week period during August and September 1967. These show, in particular, the structure and motion over the continent of Africa of four major wave disturbances, three of which later became Atlantic hurricanes. The evolution of cloudiness and convection and the intensification of the disturbance at low levels over West Africa are examined in detail and related to certain climatological features of the area. Some general characteristics of the disturbances are discussed.
Abstract
During October 12–15, 1965, the southern part of Florida received an unusually heavy and prolonged rainstorm. Although the conventional isobaric analyses did not reveal any obvious pre-existing disturbance which would be expected to produce such a result, isentropic charts suggest that intense convection was being initiated and sustained by an organized lift of conditionally unstable air to saturation. Accompanying the heavy rainfall was the formation in the lower troposphere during the 14th of a tropical depression which is thought to have been of convective origin.
Abstract
During October 12–15, 1965, the southern part of Florida received an unusually heavy and prolonged rainstorm. Although the conventional isobaric analyses did not reveal any obvious pre-existing disturbance which would be expected to produce such a result, isentropic charts suggest that intense convection was being initiated and sustained by an organized lift of conditionally unstable air to saturation. Accompanying the heavy rainfall was the formation in the lower troposphere during the 14th of a tropical depression which is thought to have been of convective origin.
Abstract
Analyses drawn from the synoptic data gathered over the eastern Caribbean in Project ECCRO, October 1965, revealed the presence of an upper tropospheric cold Low. (With assumption of state motion), the fields of wind, height, temperature, water vapor, vertical velocity, clouds, and weather were transferred to a relative coordinate system traveling with the motion of the cold Low. This process yielded composite fields in which the 6 days of data were combined into 1. These fields, showing the structure of the cold Low at five different levels in the troposphere, are presented and the evolution of cloud and moisture patterns are discussed.
Abstract
Analyses drawn from the synoptic data gathered over the eastern Caribbean in Project ECCRO, October 1965, revealed the presence of an upper tropospheric cold Low. (With assumption of state motion), the fields of wind, height, temperature, water vapor, vertical velocity, clouds, and weather were transferred to a relative coordinate system traveling with the motion of the cold Low. This process yielded composite fields in which the 6 days of data were combined into 1. These fields, showing the structure of the cold Low at five different levels in the troposphere, are presented and the evolution of cloud and moisture patterns are discussed.
Abstract
Using VHRR brightness data obtained from the NOAA 3 satellite, isopleths of aerosol Optical depth for Saharan dust have been drawn for seven days during summer 1974 over a portion of the eastern equatorial North Atlantic. The large-scale patterns reveal an elongated dust plume which emerges from a narrow region along the African coast. Thereafter, the plume moves westward and spreads laterally though maintaining rather discrete boundaries associated with sharp gradients of turbidity, especially along the southern border. Exceptionally large values of optical depth (>2.0) are found near the centers of some dust outbreaks but these high values contribute Little to the total dust loading, which, in typical episodes, are estimated to represent a loss of topsoil from Africa of ∼8 million metric tons of material in a period of 4–5 days. There appeared to be no direct intrusion of the dust plume into the ITCZ or north of 25°N in that region. Outbreaks of dust appear often to be no to the rear of a well-de-veloped easterly wave disturbance and inverted V-shaped cloud pattern. This paper demonstrates the feasibility of using satellite brightness data to quantitatively map dust outbreaks.
Abstract
Using VHRR brightness data obtained from the NOAA 3 satellite, isopleths of aerosol Optical depth for Saharan dust have been drawn for seven days during summer 1974 over a portion of the eastern equatorial North Atlantic. The large-scale patterns reveal an elongated dust plume which emerges from a narrow region along the African coast. Thereafter, the plume moves westward and spreads laterally though maintaining rather discrete boundaries associated with sharp gradients of turbidity, especially along the southern border. Exceptionally large values of optical depth (>2.0) are found near the centers of some dust outbreaks but these high values contribute Little to the total dust loading, which, in typical episodes, are estimated to represent a loss of topsoil from Africa of ∼8 million metric tons of material in a period of 4–5 days. There appeared to be no direct intrusion of the dust plume into the ITCZ or north of 25°N in that region. Outbreaks of dust appear often to be no to the rear of a well-de-veloped easterly wave disturbance and inverted V-shaped cloud pattern. This paper demonstrates the feasibility of using satellite brightness data to quantitatively map dust outbreaks.
Abstract
The development and motion of fronts associated with lee-side troughs on large mountain barriers has been investigated. These fronts differ from ordinary cold fronts in their horizontal temperature field, which is characterized by a sinusoidal thermal ridge. The thermal ridge intensifies, while remaining stationary with respect to the mountains, and moves eastward upon the approach of a Pacific cold front.
An equation is derived, showing that changes in the thermal pattern can be described by changes in a potential thermal vorticity equation, which consists of three terms: (1) one representing an advection of the potential thermal vorticity by the 500-mb. wind; (2) one representing the advection of 500-mb. absolute vorticity by the thermal wind; and (3) a purely orographic term.
An idealized sinusoidal model of the thickness pattern is used in conjunction with the prognostic equation to explain the development and motion of lee-side thermal ridges. Actual examples from synoptic maps are chosen to corroborate the theory. The conclusions are: (1) the thermal ridge will develop when the surface flow is such as to produce large-scale descent on the lee slopes of the mountains; (2) no thermal ridging will appear when the 500-mb. ridge lies east of the lee slopes; (3) thermal ridging will appear with the approach of a 500-mb. ridge from the west; and (4) the thermal ridge will move eastward upon the passage of the 500-mb. ridge.
Abstract
The development and motion of fronts associated with lee-side troughs on large mountain barriers has been investigated. These fronts differ from ordinary cold fronts in their horizontal temperature field, which is characterized by a sinusoidal thermal ridge. The thermal ridge intensifies, while remaining stationary with respect to the mountains, and moves eastward upon the approach of a Pacific cold front.
An equation is derived, showing that changes in the thermal pattern can be described by changes in a potential thermal vorticity equation, which consists of three terms: (1) one representing an advection of the potential thermal vorticity by the 500-mb. wind; (2) one representing the advection of 500-mb. absolute vorticity by the thermal wind; and (3) a purely orographic term.
An idealized sinusoidal model of the thickness pattern is used in conjunction with the prognostic equation to explain the development and motion of lee-side thermal ridges. Actual examples from synoptic maps are chosen to corroborate the theory. The conclusions are: (1) the thermal ridge will develop when the surface flow is such as to produce large-scale descent on the lee slopes of the mountains; (2) no thermal ridging will appear when the 500-mb. ridge lies east of the lee slopes; (3) thermal ridging will appear with the approach of a 500-mb. ridge from the west; and (4) the thermal ridge will move eastward upon the passage of the 500-mb. ridge.
Abstract
A statistical analysis of the effects of lower-tropospheric inversions (called lids) on deep convection was made using a “logistic” model and reports of deep convection for a six month period over the central two-thirds of the United States during 1982. Observations consist of radar echo intensity, radar echo height and direct reports of severe storm sightings or damage. We find that both the lid strength and buoyancy (lifted index) effects need to be considered jointly. Lid strength appears to exhibit an effective cutoff value, above which deep convection becomes relatively unlikely, even for unstable values of the buoyancy term. On the other hand, deep convection is unlikely for stable buoyancy values. Further, for a given value of buoyancy the probability of severe convection increases with increasing lid strength, although the total probability of deep convection diminished with increasing lid strength. This result seems to support the idea that the lid allows high values of θ w to form near the surface and that a favorable location for the release of the latent instability is along the lateral boundary of the lid. The primary value in examining both buoyancy and lid strength separately is that the method helps to eliminate large areas from consideration by the forecaster where the air near the surface is latently unstable but unlikely to produce deep convection due to the presence of a lid.
Abstract
A statistical analysis of the effects of lower-tropospheric inversions (called lids) on deep convection was made using a “logistic” model and reports of deep convection for a six month period over the central two-thirds of the United States during 1982. Observations consist of radar echo intensity, radar echo height and direct reports of severe storm sightings or damage. We find that both the lid strength and buoyancy (lifted index) effects need to be considered jointly. Lid strength appears to exhibit an effective cutoff value, above which deep convection becomes relatively unlikely, even for unstable values of the buoyancy term. On the other hand, deep convection is unlikely for stable buoyancy values. Further, for a given value of buoyancy the probability of severe convection increases with increasing lid strength, although the total probability of deep convection diminished with increasing lid strength. This result seems to support the idea that the lid allows high values of θ w to form near the surface and that a favorable location for the release of the latent instability is along the lateral boundary of the lid. The primary value in examining both buoyancy and lid strength separately is that the method helps to eliminate large areas from consideration by the forecaster where the air near the surface is latently unstable but unlikely to produce deep convection due to the presence of a lid.
Abstract
A one-dimensional numerical model, capable of simulating surface temperature and heat flux, is described in terms of the effective atmospheric and terrain variables. The two model parameters which are most responsible for the formation of important temperature variations in the horizontal over the urban-rural complex are the thermal inertia (thermal property) and moisture availability, the former being most responsible for shaping the nighttime temperature pattern while the latter has a greater effect during the day.
The controlling substrate variables are not easily determinable by direct measurement over a surface consisting of an inhomogeneous agglomerate of elements. We present one method whereby surface temperature, a more readily obtainable quantity, can be used in conjunction with the surface model to determine by numerical or graphical inversion of the latter the effective values of moisture availability and thermal inertia and thereby provide a quantitative framework for analysis of a rough surface and for an evaluation of the surface energy budget.
Abstract
A one-dimensional numerical model, capable of simulating surface temperature and heat flux, is described in terms of the effective atmospheric and terrain variables. The two model parameters which are most responsible for the formation of important temperature variations in the horizontal over the urban-rural complex are the thermal inertia (thermal property) and moisture availability, the former being most responsible for shaping the nighttime temperature pattern while the latter has a greater effect during the day.
The controlling substrate variables are not easily determinable by direct measurement over a surface consisting of an inhomogeneous agglomerate of elements. We present one method whereby surface temperature, a more readily obtainable quantity, can be used in conjunction with the surface model to determine by numerical or graphical inversion of the latter the effective values of moisture availability and thermal inertia and thereby provide a quantitative framework for analysis of a rough surface and for an evaluation of the surface energy budget.
