Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: M. A. Alaka x
  • Monthly Weather Review x
  • Refine by Access: All Content x
Clear All Modify Search
M. A. ALAKA

Abstract

Observations made by the specially instrumented aircraft, operated by the National Hurricane Research Project, establish the occurrence of dynamic instability, notably in the form of anomalous winds in the upper troposphere above hurricane Daisy, shortly after its inception. It is inferred that the dynamic instability released by these anomalous winds, which represent anticyclonic rotation in space, triggered Daisy's development.

Since the observed dynamic instability occurred on a mesoscale, the above inference is not amenable to direct verification from synoptic maps. However, synoptic conditions favorable for the development of anomalous winds are discussed and it is found that these conditions prevailed in the upper troposphere directly above Daisy and Gracie a short time before they reached hurricane intensity.

The role of negative absolute vorticity is shown to vary. In the presence of anomalous winds it is a stabilizing factor which is nonetheless important in channeling outflow at the top of the hurricane. With normal winds, negative absolute vorticity is a destabilizing agent and some evidence is presented that it may also be responsible for initiating the development of certain hurricanes.

Full access
M. A. ALAKA

Abstract

Observational evidence is provided for the occurrence of anomalous winds which represent an anticyclonic rotation in space, and a mechanism for their development is suggested. The unstable nature of these winds and the role they play in the development of certain types of atmospheric disturbances is then discussed, and it is suggested that anomalous winds provide the dynamic mechanism for triggering hurricane formation and for the observed deepening of troughs downstream from intense pressure ridges. Finally it is noted that although the observational evidence presented is for the occurrence of anomalous winds over small regions of the atmosphere, their development is dependent on large-scale processes and their effect extends beyond the area where they occur.

Full access
M. A. ALAKA
and
D. T. RUBSAM

Abstract

Observations made at different levels by aircraft of the Research Flight Facility (RFF) of the U.S. Weather Bureau, in conjunction with regular synoptic observations from the coastal United States and Bahamas, are utilized in detailed analysis of conditions prevailing during the crucial period immediately before, during, and after Ella (1962) attained hurricane intensity.

It is shown that, in contrast with other hurricanes described in the literature, Ella did not develop under an upper tropospheric anticyclone. Rather, anticyclonic circulation first appeared in the middle troposphere and gradually extended upward while the storm was intensifying into a hurricane. Correspondingly, the warm-core structure first appeared in the low levels and then spread to the upper troposphere.

Full access