Abstract
Abstract. A system to derive tracks of barometric minima is presented. It is deliberately using coarse input data in space (order of 2°×2°) and time (6-hourly to daily) as well as information from just one geopotential level. It is argued that the results are, for one robust in the sense of an assumption of the IMILAST Project that the use of as simple as possible metrics should be strived for and for two tailored to the input from reanalyses and GCMs. The methodology presented is a necessary first step towards an automated storm track recognition scheme which will be employed in a second paper to study the future development of atmospheric dynamics in a changing climate. The process towards obtaining storm tracks is two-fold. In its first step cyclone centers are being identified. The performance of this step requires the existence of closed isolines, i.e., a topology in which a grid-point is surrounded by neighbours which all exhibit higher geopotential. The usage of this topology requirement as well as the constraint of coarse data may lead, though, to limitations in identifying centers in geopotential fields with shallow gradients that may occur in the summer months; moreover, some centers may potentially be missed in case of a configuration in which a small scale storm is located at the perimeter of a deep and very large low (a kind of "dent in a crater wall"). The second step of the process strings the identified cyclone centers together in a meaningful way to form tracks. By way of several examples the capability to identify known storm tracks is shown.
Highlights
This study focuses on the identification and tracking of moving low pressure systems
In its first step cyclone centers are being identified. The performance of this step requires the existence of closed isolines, i.e., a topology in which a grid-point is surrounded by neighbours which all exhibit higher geopotential
The usage of this topology requirement as well as the constraint of coarse data may lead, though, to limitations in identifying centers in geopotential fields with shallow gradients that may occur in the summer months; some centers may potentially be missed in case of a configuration in which a small scale storm is located at the perimeter of a deep and very large low
Summary
This study focuses on the identification and tracking of moving low pressure systems. The method applied has large scale as well as regional scale elements – the data source for the the identification consists of NCAR reanalysis data (Kalnay et al, 1996) from 1951–2006 Developing such an algorithm on a rather coarse spatially and temporally resolved basis leads to a robust tool to address issues such as the classification of dynamic circulation aspects and the study of cyclone tracks, e.g., in global climate model data. 850 hPa geopotential height data from NCEP reanalyses (Kalnay et al, 1996) were used in the study to develop the identification methods for cyclone centers and tracks. They establish a three-dimensional climatology of the atmosphere for the time frame 1950 until now. Some cyclone centers in subsequent figures might not have been labelled, since they are outside this area
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