School of Earth Sciences - Research Publications

Permanent URI for this collection

Search Results

Now showing 1 - 4 of 4
  • Item
    Thumbnail Image
    Variability and Trends of Global Atmospheric Frontal Activity and Links with Large-Scale Modes of Variability
    Rudeva, I ; Simmonds, I (AMER METEOROLOGICAL SOC, 2015-04)
    Abstract Presented here is a global analysis of frontal activity variability derived from ERA-Interim data over the 34-yr period of January 1979–March 2013 using a state-of-the-art frontal tracking scheme. In December–February over that epoch, there is a northward shift of frontal activity in the Pacific in the Northern Hemisphere (NH). In the Southern Hemisphere (SH), the largest trends are identified in the austral summer and are manifested by a southward shift of frontal activity over the Southern Ocean. Variability of frontal behavior is found to be closely related to the main modes of atmospheric circulation, such as the North Atlantic Oscillation (NAO) for the Atlantic–European sector in the NH and the southern annular mode (SAM) in the middle and high latitudes of the SH. A signal associated with El Niño and hence emanating from the tropics is also apparent in the behavior of frontal systems over the Pacific by a reduction in the number of fronts in the middle South Pacific and intensification of frontal activity in high and low latitudes throughout the year. It is shown in general that the associations of the large-scale modes with frontal variability are much stronger than with cyclones. This indicates that the quantification of the behavior of fronts is an important component of understanding the climate system. At the very high latitudes, it is also shown here that, in the recent years of rapid sea ice reduction in the Arctic, there have been fewer summer fronts observed over the Canadian Arctic.
  • Item
    Thumbnail Image
    Seasonal Aspects of an Objective Climatology of Anticyclones Affecting the Mediterranean
    Hatzaki, M ; Flocas, HA ; Simmonds, I ; Kouroutzoglou, J ; Keay, K ; Rudeva, I (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.
  • Item
    Thumbnail Image
    A comparison of tracking methods for extreme cyclones in the Arctic basin
    Simmonds, I ; Rudeva, I (CO-ACTION PUBLISHING, 2014)
  • Item
    Thumbnail Image
    The sensitivity of characteristics of cyclone activity to identification procedures in tracking algorithms
    Rudeva, I ; Gulev, SK ; Simmonds, I ; Tilinina, N (TAYLOR & FRANCIS LTD, 2014)