The effects of ENSO‐types and SAM on the large‐scale southern blockings

Abstract

In this observational study, the effects of the two types (Canonical and Modoki) of El Niño – Southern Oscillation (ENSO) and Southern Annular Mode (SAM) on the large‐scale southern blockings are investigated using the NCEP Climate Forecast System Reanalysis (CFSR) dataset. The automated 2D blocking index used here removes those structures that do not represent a typical blocking pattern. The daily SAM and monthly ENSO indices are defined when their time coefficient of the empirical orthogonal function is above or below 0.5 and 1.0 standard deviation, respectively. This study indicates that the El Niño Modoki is the most favourable ENSO mechanism for blocking events during the southern cool season. In particular, when El Niño Modoki occurs with positive SAM and/or weak SAM it acts to increase the number of days of blocking over the Southwest Pacific, or when it occurs with the negative SAM acts to maintain the observed number of days of blocking over the Southeast Pacific. Also, increases in the number of days of blocking are found in the warm season over the Southeast Pacific when the canonical El Niño occurs with negative SAM. On the other hand, the long‐term change in the annual number of days of blocking shows a strong (moderate) downward linear trend over the Southwest (Southeast) Pacific, as well as the two types of La Niña, their temporal distribution with a positive SAM appears as the major cause.

Multi-century cool and warm season rainfall reconstructions for Australia's major climatic regions

“…There have been a number of palaeoclimate reconstructions of hydrological variables in Australia (Allen et al, 2015;Cullen and Grierson, 2008;Gallant and Gergis, 2011;Gergis et al, 2011;Heinrich et al, 2009;Lough et al, 2015). Palmer et al (2015) recently introduced the Australia and New Zealand Drought Atlas (ANZDA), using the approach developed for Asia (Monsoon Asia Drought Atlas (MADA) (Cook et al, 2010)), Europe (Old World Drought Atlas (OWDA) (E. R. ) and North America by Cook et al (2010). The ANZDA reconstructs the past 500 years of the Palmer Drought severity index (PDSI) for a 0.5 • ×0.5 • grid over eastern Australia and New Zealand using a network of 176 tree-ring records and one coral record.…”

Linkages between stratospheric ozone, UV radiation and climate change and their implications for terrestrial ecosystems

“…4 Specifically, ozone depletion appears to be changing regional atmospheric circulation patterns in the southern hemisphere which, in turn, affect weather conditions, sea surface temperatures, and frequency of wildfires. [58][59][60][61][62] These changes together with changes in UV-B radiation can have several consequences for terrestrial ecosystems (see section 3.2, Fig. 3, and Table 1).…”

Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future

“…Climate change can modify depletion of stratospheric ozone by perturbing temperature, moisture, and wind speed and direction in the stratosphere and troposphere 24 ; and certain greenhouse gases (e.g., N2O and CH4) can affect ozone levels. 12 Conversely, it is now clear that ozone depletion in the southern hemisphere is directly contributing to climate change by altering regional atmospheric circulation patterns in this part of the globe 25 which affects weather conditions, sea surface temperatures, ocean currents, and the frequency of wildfires [26][27][28][29][30] . These ozone-driven changes in climate are currently exerting significant impacts on the terrestrial and aquatic ecosystems in this region [31][32][33][34] (Box 3).…”

“…Stratospheric ozone depletion has been a dominant driver of changes in Southern Hemisphere summer climate over the later part of the 20 th Century, moving the winds and associated latitudinal bands of high and low rainfall further south [23][24][25][26][27][28][29][30]34 (inset globe). As a result, aquatic and terrestrial ecosystems, including agriculture, have been affected in several ways 31,32 .…”