The Continuum of Wintertime Southern Hemisphere Atmospheric Teleconnection Patterns*,+

Abstract

This study uses the method of self-organizing maps (SOMs) to categorize the June–August atmospheric teleconnections in the 500-hPa geopotential height field of the Southern Hemisphere (SH) extratropics. This approach yields 12 SOM patterns that provide a discretized representation of the continuum of SH teleconnection patterns from 1979 to 2012. These 12 patterns are large in spatial scale, exhibiting a mix of annular mode characteristics and wave trains of zonal wavenumber varying from 2 to 4. All patterns vary with intrinsic time scales of about 5–10 days, but some patterns exhibit quasi-oscillatory behavior over a period of 20–30 days, whereas still others exhibit statistically significant enhanced and suppressed frequencies up to about four weeks in association with the Madden–Julian oscillation. Two patterns are significantly influenced by El Niño–Southern Oscillation (ENSO) on interannual time scales. All 12 patterns have strong influences on surface air temperature and sea ice concentrations, with the sea ice response occurring over a time scale of about 2–4 weeks. The austral winter has featured a positive frequency trend in patterns that project onto the negative phase of the southern annular mode (SAM) and a negative frequency trend in positive SAM-like patterns. Such atmospheric circulation trends over 34 yr may arise through atmospheric internal variability alone, and, unlike other seasons in the SH, it is not necessary to invoke external forcing as a dominant source of circulation trends.

Review of Tropical‐Extratropical Teleconnections on Intraseasonal Time Scales

“…Matthews and Meredith (2004) demonstrated that the austral winter southern hemisphere annular mode strengthens about 7 days after the peak in Indian Ocean MJO convection. A recent study by Chang and Johnson (2015) identified teleconnection patterns in the midlatitudes of Southern Hemisphere winter that exhibit oscillatory behavior on time scales of 20-30 days and with the frequency of occurrence modulated by the MJO phases. These patterns mix characteristics of the southern hemisphere annular modes (Limpasuvan & Hartmann, 1999;Thompson & Woodworth, 2014) and the asymmetric PSA modes.…”

Role of seasonal transitions and the westerlies in the interannual variability of the East Asian summer monsoon precipitation

“…The SOM method is a neural network-based cluster analysis that classifies a high-dimensional data set into representative patterns, using a neighborhood function to topologically order the high-dimensional input and group similar clusters together [Kohonen, 1998]. The SOM has recently been used to extract patterns of climate variation such as the El Niño-Southern Oscillation [Johnson, 2013] and Northern and Southern Hemisphere teleconnection patterns [Chang and Johnson, 2015;Johnson et al, 2008]. In addition, Chattopadhyay et al [2008] employed SOM analysis to characterize intraseasonal oscillation of the Indian summer monsoon, and Chu et al [2012] used it to extract intraseasonal modes of the East Asian-western North Pacific summer monsoon.…”

Antarctic Cloud Macrophysical, Thermodynamic Phase, and Atmospheric Inversion Coupling Properties at McMurdo Station—Part II: Radiative Impact During Different Synoptic Regimes

“…This choice provides nine synoptic modes in total. Previous studies described ways to objectively examine if SOM patterns are distinguishable when the data samples are independent or weakly dependent (e.g., Chang & Johnson, ; Johnson, ). However, as the consecutive maps used in this study are highly dependent, there is no objective method (to the extent of the authors knowledge) to examine whether the SOM patterns are distinguishable.…”