School of Earth Sciences - Research Publications
Permanent URI for this collection
Search Results
1 - 7 of 7
-
Item
-
Item
-
ItemSeasonal Aspects of an Objective Climatology of Anticyclones Affecting the Mediterranean(AMER METEOROLOGICAL SOC, 2014-12)Abstract An objective climatology of anticyclones over the greater Mediterranean region is presented based on the Interim ECMWF Re-Analysis (ERA-Interim) for a 34-yr period (1979–2012) and the Melbourne University automatic identification and tracking algorithm. The scheme’s robustness and reliability for the transient extratropical propagation of anticyclones, with the appropriate choices of parameter settings, has been established and the results obtained here present new research perspectives on anticyclonic activity affecting the Mediterranean. Properties of Mediterranean anticyclones, such as frequency, generation and dissipation, movement, scale, and depth are investigated. The highest frequency of anticyclones is found over continental areas, while the highest maritime frequency occurs over closed basins exhibiting also maxima of anticyclogenesis. There is a significant seasonality in system density and anticyclogenesis maxima, this being associated with the seasonal variations of the larger-scale atmospheric circulation that affect the greater Mediterranean region.
-
ItemIdentification and Climatology of Southern Hemisphere Mobile Fronts in a Modern Reanalysis(AMER METEOROLOGICAL SOC, 2012-03-15)Abstract Presented here is an objective approach to identify, characterize, and track Southern Hemisphere mobile fronts in hemispheric analyses of relatively modest resolution, such as reanalyses. Among the principles in its design were that it should be based on broadscale synoptic considerations and be as simple and easily understood as possible. The resulting Eulerian scheme has been applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA)–Interim and a climatology of frontal characteristics, at both the 10-m and 850-hPa levels, derived for the period 1 January 1989–28 February 2009. The knowledge of the character of these features is central to understanding weather and climate over the hemisphere. In both summer and winter the latitude belt 40°–60°S hosts the highest frequency of frontal points, but there are significant zonal asymmetries within this band. The climatology reveals that the longest fronts are in the Indian Ocean where mean lengths exceed 2000 km. The mean frontal intensity over the hemisphere tends to be greater at 850 hPa than at 10 m, and greater in winter than in summer. The frontal intensity also shows its maximum in the Indian Ocean. In the mean, the meridional tilt of these fronts is northwest–southeast over much of the midlatitudes and subtropics, and increases with latitude toward the equator. The tilts are of overwhelmingly opposite sign in the coastal Antarctic and subantarctic regions. Broadly speaking, the number of fronts and their mean length and mean intensity exhibit maxima in winter in the midlatitudes (30°–50°S), but show a sizeable semiannual variation (maxima in fall and spring) during the year at higher latitudes.
-
ItemNew perspectives on the synoptic development of the severe October 1992 Nome storm(AMER GEOPHYSICAL UNION, 2009-07-14)Understanding the characteristics of storms that impact the Alaska region is of importance to emergency planning. The 5–7 October 1992 storm was a severe event which cost Nome, a town in Alaska, $6 million dollars. We will explore its characteristics with the aid of two established cyclone tracking schemes: the NOAA CPC current operational algorithm and the University of Melbourne algorithm. Manual tracking was performed as a control. The essential features are captured by both algorithms, but they differ in the genesis and lysis location. The NOAA algorithm broke the storm into two separate events. Synoptic development of the storm was influenced by a blocking high that affected how the tracking algorithms handled the event. A synoptic re‐examination of this storm is presented in terms of the depth, Laplacian and radius of the system. These new results present a fresh perspective on the intensity and longevity of this dramatic storm.
-
ItemExtraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979-2008(American Geophysical Union, 2009)Dramatic changes have been observed in Arctic sea ice, cyclone behavior and atmospheric circulation in recent decades. Decreases in September ice extent have been remarkable over the last 30 years, and particularly so in very recent times. The analysis reveals that the trends and variability in September ice coverage and mean cyclone characteristics are related, and that the strength (rather than the number) of cyclones in the Arctic basin is playing a central role in the changes observed in that region, especially in the last few years. The findings reinforce suggestions that the decline in the extent and thickness of Arctic ice has started to render it particularly vulnerable to future anomalous cyclonic activity and atmospheric forcing.
-
ItemRelationships between Antarctic cyclones and surface conditions as derived from high-resolution numerical weather prediction data(AMER GEOPHYSICAL UNION, 2011-04-14)