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1. Introduction The intraseasonal oscillation (ISO) characterized by a 20–60-day period is typically referred to as the dominant mode of intraseasonal variability of the tropics. In boreal winter, ISO is often represented by the Madden–Julian oscillation (MJO) propagating eastward along the equator ( Madden and Julian 1972 , 1994 ; Wheeler and Hendon 2004 ; Zhang 2005 ). Boreal summer ISO (BSISO) frequently originates in the western and central equatorial Indian Ocean (IO) ( Yasunari 1979
1. Introduction The intraseasonal oscillation (ISO) characterized by a 20–60-day period is typically referred to as the dominant mode of intraseasonal variability of the tropics. In boreal winter, ISO is often represented by the Madden–Julian oscillation (MJO) propagating eastward along the equator ( Madden and Julian 1972 , 1994 ; Wheeler and Hendon 2004 ; Zhang 2005 ). Boreal summer ISO (BSISO) frequently originates in the western and central equatorial Indian Ocean (IO) ( Yasunari 1979
1. Introduction Oscillations in OGCMs under mixed surface boundary conditions (restoring on surface temperature, imposed freshwater flux) have now been widely reported and are found to occur in several frequency bands: decadal, centennial, millennial [see the reviews by Weaver and Hughes (1992) and Dijkstra and Ghil (2005) ]. A strong incentive for a better understanding of the oscillations of the thermohaline circulation (THC) comes from the paleoclimatic evidence originating from ice cores
1. Introduction Oscillations in OGCMs under mixed surface boundary conditions (restoring on surface temperature, imposed freshwater flux) have now been widely reported and are found to occur in several frequency bands: decadal, centennial, millennial [see the reviews by Weaver and Hughes (1992) and Dijkstra and Ghil (2005) ]. A strong incentive for a better understanding of the oscillations of the thermohaline circulation (THC) comes from the paleoclimatic evidence originating from ice cores
1. Introduction Intraseasonal variation (ISV) modes generally comprise the 30–60-day oscillation [also known as the Madden–Julian oscillation (MJO; Madden and Julian 1971 ) in the boreal winter and boreal summer intraseasonal oscillation (BSISO; Wang and Xie 1997 )] and 10–20-day oscillation [also referred to as the quasi-biweekly oscillation (QBWO)]. Madden and Julian (1971) were the first to detect the 30–60-day oscillation in the tropical Pacific and confirmed that it exists over the
1. Introduction Intraseasonal variation (ISV) modes generally comprise the 30–60-day oscillation [also known as the Madden–Julian oscillation (MJO; Madden and Julian 1971 ) in the boreal winter and boreal summer intraseasonal oscillation (BSISO; Wang and Xie 1997 )] and 10–20-day oscillation [also referred to as the quasi-biweekly oscillation (QBWO)]. Madden and Julian (1971) were the first to detect the 30–60-day oscillation in the tropical Pacific and confirmed that it exists over the
1. Introduction Understanding and predicting the variability of large-scale teleconnections are important to correctly predict atmospheric circulation and climate anomalies in different regions. There are many large-scale atmospheric teleconnections, such as the North Atlantic Oscillation (NAO; Walker and Bliss 1932 ), the North Pacific Oscillation (NPO; Rogers 1981 ), the Pacific–North American (PNA) pattern ( Wallace and Gutzler 1981 ), and the Pacific–Japan (PJ) pattern ( Nitta 1986
1. Introduction Understanding and predicting the variability of large-scale teleconnections are important to correctly predict atmospheric circulation and climate anomalies in different regions. There are many large-scale atmospheric teleconnections, such as the North Atlantic Oscillation (NAO; Walker and Bliss 1932 ), the North Pacific Oscillation (NPO; Rogers 1981 ), the Pacific–North American (PNA) pattern ( Wallace and Gutzler 1981 ), and the Pacific–Japan (PJ) pattern ( Nitta 1986
rainfall variability. For instance, decadal variability has long been known to be a feature of the southern African climate system data ( Neukom et al. 2014 ; Reason and Rouault 2002 ; Tyson 1986 ). The presence of the approximately 18-yr climate oscillation has been identified in instrumental and tree-ring series ( Tyson et al. 2002a ; Visagie 1985 ), as well as in a recent precipitation reconstruction from the last 200 years ( Neukom et al. 2014 ). A 16–20-yr band has also been observed in ocean
rainfall variability. For instance, decadal variability has long been known to be a feature of the southern African climate system data ( Neukom et al. 2014 ; Reason and Rouault 2002 ; Tyson 1986 ). The presence of the approximately 18-yr climate oscillation has been identified in instrumental and tree-ring series ( Tyson et al. 2002a ; Visagie 1985 ), as well as in a recent precipitation reconstruction from the last 200 years ( Neukom et al. 2014 ). A 16–20-yr band has also been observed in ocean
oscillations with periods varying from 18 to 25 years. They also showed that these periodicities vary over time, in particular during the 1950–70 decades when higher variability predominated. In the southern high latitudes, Zazulie et al. (2010) analyzed T-air variations in the Antarctic South Orkney/Orcadas del Sur Island station (60.7°S, 44.7°W) and found no statistically significant trends from 1903 to 1950; however, for the remainder of the series a statistically significant warming was noticed
oscillations with periods varying from 18 to 25 years. They also showed that these periodicities vary over time, in particular during the 1950–70 decades when higher variability predominated. In the southern high latitudes, Zazulie et al. (2010) analyzed T-air variations in the Antarctic South Orkney/Orcadas del Sur Island station (60.7°S, 44.7°W) and found no statistically significant trends from 1903 to 1950; however, for the remainder of the series a statistically significant warming was noticed
1. Introduction Since Madden and Julian (1972) found the eastward-propagating oscillations over the tropical Indo-Pacific region, many observational analyses have revealed a slowly eastward-propagating convective envelope characterized by planetary-scale circulation with a broad life span of 30–60 days (e.g., Lau and Chan 1986 ; Hendon and Salby 1994 ; Zhang 2005 ; Lau and Waliser 2005 ). Despite numerous studies about the Madden–Julian oscillation (MJO), some fundamental questions still
1. Introduction Since Madden and Julian (1972) found the eastward-propagating oscillations over the tropical Indo-Pacific region, many observational analyses have revealed a slowly eastward-propagating convective envelope characterized by planetary-scale circulation with a broad life span of 30–60 days (e.g., Lau and Chan 1986 ; Hendon and Salby 1994 ; Zhang 2005 ; Lau and Waliser 2005 ). Despite numerous studies about the Madden–Julian oscillation (MJO), some fundamental questions still
1. Introduction There is a considerable body of observations from Greenland ice cores and deep sea sediments that shows that the Greenland climate has undergone quasiperiodic oscillations of 1.5 kyr period with O (10°C) air temperature variations during the last glacial period [see the reviews by Alley et al. (1999) , National Research Council Committee on Abrupt Climate Change (2002) , Dansgaard et al. (1993) , Grootes et al. (1993) , and Severinghaus and Brook (1999) ]. Active
1. Introduction There is a considerable body of observations from Greenland ice cores and deep sea sediments that shows that the Greenland climate has undergone quasiperiodic oscillations of 1.5 kyr period with O (10°C) air temperature variations during the last glacial period [see the reviews by Alley et al. (1999) , National Research Council Committee on Abrupt Climate Change (2002) , Dansgaard et al. (1993) , Grootes et al. (1993) , and Severinghaus and Brook (1999) ]. Active
1. Introduction The Madden–Julian oscillation ( Madden and Julian 1971 , 2005 ) is the dominant component of intraseasonal variability in the tropical atmosphere. It is characterized by eastward-propagating, equatorially trapped, baroclinic oscillations in the tropical wind field. During a typical MJO event, a positive convection/rainfall anomaly develops over the western Indian Ocean, while convection tends to be suppressed further east over the western Pacific. Over the course of the
1. Introduction The Madden–Julian oscillation ( Madden and Julian 1971 , 2005 ) is the dominant component of intraseasonal variability in the tropical atmosphere. It is characterized by eastward-propagating, equatorially trapped, baroclinic oscillations in the tropical wind field. During a typical MJO event, a positive convection/rainfall anomaly develops over the western Indian Ocean, while convection tends to be suppressed further east over the western Pacific. Over the course of the
1. Introduction The North Atlantic Oscillation (NAO) is the dominant mode of boreal winter climate variability over the North Atlantic ( Walker and Bliss 1932 ; Barnston and Livezey 1987 ). The NAO is strongly linked to patterns of winter temperature, precipitation, and storminess over the whole North Atlantic sector ( Hurrell 1995 ; Trigo et al. 2002 ). Accurate and timely forecasts of the winter NAO are therefore an important challenge for seasonal forecasters and increasing research is
1. Introduction The North Atlantic Oscillation (NAO) is the dominant mode of boreal winter climate variability over the North Atlantic ( Walker and Bliss 1932 ; Barnston and Livezey 1987 ). The NAO is strongly linked to patterns of winter temperature, precipitation, and storminess over the whole North Atlantic sector ( Hurrell 1995 ; Trigo et al. 2002 ). Accurate and timely forecasts of the winter NAO are therefore an important challenge for seasonal forecasters and increasing research is
