Toby N. Carlson

Airflow Through Midlatitude Cyclones and the Comma Cloud Pattern

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.

SYNOPTIC HISTORIES OF THREE AFRICAN DISTURBANCES THAT DEVELOPED INTO ATLANTIC HURRICANES

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.

SOME REMARKS ON AFRICAN DISTURBANCES AND THEIR PROGRESS OVER THE TROPICAL ATLANTIC

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.

Sensitivity of the Great Plains Severe-Storm Environment to Soil-Moisture Distribution

Abstract This study examines the influence of differences in ground moisture over the southern Great Plairs and the Mexican plateau on the formation and evolution of the dryline, the elevated mixed layer, and the local planetary boundary layer. These features are examined in a series of numerical experiments in which dry and wet surface conditions over the southern plains and Mexico are simulated by the model Results of the numerical simulations show that the dry soil conditions of northern Mexico are critical to the formation of the lid, and the variable soil conditions of the southern Great Plains are important for the processes of differential surface heating and generation of low-level instability through strong surface evaporation. The processes interact dynamically to alter the prestorm conditions and subsequent convective patterns observed over Texas and Oklahoma in the SESAME IV case.

Atmospheric Turbidity in Saharan Dust Outbreaks as Determined by Analyses of Satellite Brightness Data

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-...

WEATHER NOTE: An Apparent Relationship Between the Sea-Surface Temperature of the Tropical Atlantic and the Development of African Disturbances Into Tropical Storms

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.

STRUCTURE OF A STEADY-STATE COLD LOW

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.

LEE-SIDE FRONTOGENESIS IN THE ROCKY MOUNTAINS1

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...

VERTICAL MOTIONS AND THE KINETIC ENERGY BALANCE OF A COLD LOW

Abstract Vertical motions have been computed for a 6-day period during which an upper tropospheric cold Low moved through the eastern Caribbean, and a kinetic energy budget for the region has been constructed. During the first 3 days, the kinetic energy inside the volume increased. The computations indicate that the increase was caused by lateral advection of kinetic energy into the volume plus a small internal conversion of potential to kinetic energy. The kinetic energy decreased during the last 3 days, as the circulation became indirect. Visual agreement between the vertical motions and the observed weather was good.

Objective Analysis of Aircraft Data in Tropical Cyclones

Abstract A method for objective analysis of aircraft observations in tropical cyclones has been developed. Quasi-horizontal fields of motion, temperatures, mixing ratios, and D-values are analyzed using a modified version of the method of successive corrections. The weighting functions are specified so that the high degree of circular symmetry characteristic of tropical cyclones is incorporated in the analyses. The analyses are performed on a 25 by 25 Cartesian grid of 5 n mi spacing which is centered on the storm. A special feature is the analysis of vertical motions as determined from aircraft flight characteristics. Three Atlantic storms are analyzed in detail: Hurricanes Inez (1966), Debbie (1969), and Ginger (1971). The analyses show the significant larger-scale features and major asymmetries of these storms. Both Inez and Debbie, which were well organized hurricanes, display characteristic vertical motion patterns in which a ring of strong ascent is found immediately surrounding the eye, with marked...