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efforts. On the other hand, the debate about the physical reality of the AO continues. A historical review of the debate is described in detail in appendix A . Its brief summary is as follows: in the debate, three other modes are involved. Two of them are well-known modes: the North Atlantic Oscillation (NAO) and the Pacific–North American Oscillation (PNA). The third is the EOF second mode, whose pattern shows a negative correlation between the Atlantic and Pacific regions (hereafter abbreviated as
efforts. On the other hand, the debate about the physical reality of the AO continues. A historical review of the debate is described in detail in appendix A . Its brief summary is as follows: in the debate, three other modes are involved. Two of them are well-known modes: the North Atlantic Oscillation (NAO) and the Pacific–North American Oscillation (PNA). The third is the EOF second mode, whose pattern shows a negative correlation between the Atlantic and Pacific regions (hereafter abbreviated as
isobaric surfaces from 500 to 100 hPa. Three circulation indices are obtained from the Climate Prediction Center (CPC): the Arctic Oscillation index (AOI), the North Atlantic Oscillation index (NAOI), and the Pacific–North American pattern index (PNAI). The CPC develops the AOI by projecting monthly-mean 1000-hPa geopotential height anomalies onto the loading pattern of the first EOF of year-round, deseasonalized monthly-mean 1000-hPa geopotential height poleward of 20°N for 1979–2000. The loading
isobaric surfaces from 500 to 100 hPa. Three circulation indices are obtained from the Climate Prediction Center (CPC): the Arctic Oscillation index (AOI), the North Atlantic Oscillation index (NAOI), and the Pacific–North American pattern index (PNAI). The CPC develops the AOI by projecting monthly-mean 1000-hPa geopotential height anomalies onto the loading pattern of the first EOF of year-round, deseasonalized monthly-mean 1000-hPa geopotential height poleward of 20°N for 1979–2000. The loading
. Specifically, the extratropical response to MJO phase 1 (phase 5) projects onto the negative (positive) phase of the Pacific–North America (PNA) teleconnection pattern ( Mori and Watanabe 2008 ; Johnson and Feldstein 2010 ; Moore et al. 2010 ; Franzke et al. 2011 ; Yoo et al. 2012 ; Riddle et al. 2013 ). On the other hand, the extratropical response to El Niño (La Niña) projects onto the positive (negative) phase of the PNA (e.g., Horel and Wallace 1981 ; Wallace and Gutzler 1981 ; Trenberth et al
. Specifically, the extratropical response to MJO phase 1 (phase 5) projects onto the negative (positive) phase of the Pacific–North America (PNA) teleconnection pattern ( Mori and Watanabe 2008 ; Johnson and Feldstein 2010 ; Moore et al. 2010 ; Franzke et al. 2011 ; Yoo et al. 2012 ; Riddle et al. 2013 ). On the other hand, the extratropical response to El Niño (La Niña) projects onto the positive (negative) phase of the PNA (e.g., Horel and Wallace 1981 ; Wallace and Gutzler 1981 ; Trenberth et al
.4 ( Trenberth 1997 ), Pacific–North American pattern (PNA, Wallace and Gutzler 1981 ), and Arctic Oscillation (AO, Higgins et al. 2000 ). These indices were chosen because of their direct or indirect association with wind, temperature, and precipitation variability around Eclipse that may leave a robust proxy signal. The PDO index describes a multidecadal (~50–60-yr period) cycle in the SST anomalies in the Pacific basin (similar to ENSO). The positive phase exhibits warm anomalies in the central
.4 ( Trenberth 1997 ), Pacific–North American pattern (PNA, Wallace and Gutzler 1981 ), and Arctic Oscillation (AO, Higgins et al. 2000 ). These indices were chosen because of their direct or indirect association with wind, temperature, and precipitation variability around Eclipse that may leave a robust proxy signal. The PDO index describes a multidecadal (~50–60-yr period) cycle in the SST anomalies in the Pacific basin (similar to ENSO). The positive phase exhibits warm anomalies in the central
), Pacific decadal oscillation (PDO; Mantua et al. 1997 ), and Atlantic multidecadal oscillation (AMO; Kerr 2000 ) (e.g., Horel and Wallace 1981 ; Straus and Shukla 2002 ; Yu and Zwiers 2007 ; Zhang and Delworth 2007 ). The PNA pattern influences the direction and strength of the prevailing circulation and, thus, affects airmass frequency, moisture variability, temperature, and precipitation across many parts of continental North America. The positive phase of the PNA is associated with an increase
), Pacific decadal oscillation (PDO; Mantua et al. 1997 ), and Atlantic multidecadal oscillation (AMO; Kerr 2000 ) (e.g., Horel and Wallace 1981 ; Straus and Shukla 2002 ; Yu and Zwiers 2007 ; Zhang and Delworth 2007 ). The PNA pattern influences the direction and strength of the prevailing circulation and, thus, affects airmass frequency, moisture variability, temperature, and precipitation across many parts of continental North America. The positive phase of the PNA is associated with an increase
sets off a northeastward Rossby wave train that spreads ENSO influence ( Trenberth et al. 1998 ) via the Pacific–North America (PNA) pattern and intraseasonal Madden–Julian oscillation (MJO) ( Lopez and Kirtman 2019 ). Rossby wave amplitudes tend to grow next to diabatic heat sources when the polar vortex weakens ( Steinschneider and Lall 2016 ; Jiménez-Esteve and Domeisen 2018 ; Riboldi et al. 2022 ). Jet stream bifurcation accompanied by blocking highs can slow the eastward progression of
sets off a northeastward Rossby wave train that spreads ENSO influence ( Trenberth et al. 1998 ) via the Pacific–North America (PNA) pattern and intraseasonal Madden–Julian oscillation (MJO) ( Lopez and Kirtman 2019 ). Rossby wave amplitudes tend to grow next to diabatic heat sources when the polar vortex weakens ( Steinschneider and Lall 2016 ; Jiménez-Esteve and Domeisen 2018 ; Riboldi et al. 2022 ). Jet stream bifurcation accompanied by blocking highs can slow the eastward progression of
Niño–Southern Oscillation (ENSO; Eichler and Higgins 2006 ), the Pacific–North American pattern (PNA; Angel and Isard 1998 ), and the Madden–Julian oscillation (MJO; Lin et al. 2010 ; Becker et al. 2011 ; Zhou et al. 2012 ). However, the methodology used in these studies varies greatly and makes it challenging to interpret their results quantitatively. Previous studies have identified storm tracks using four main methods: 1) manual identification ( Klein 1957 ; Zishka and Smith 1980 ), 2
Niño–Southern Oscillation (ENSO; Eichler and Higgins 2006 ), the Pacific–North American pattern (PNA; Angel and Isard 1998 ), and the Madden–Julian oscillation (MJO; Lin et al. 2010 ; Becker et al. 2011 ; Zhou et al. 2012 ). However, the methodology used in these studies varies greatly and makes it challenging to interpret their results quantitatively. Previous studies have identified storm tracks using four main methods: 1) manual identification ( Klein 1957 ; Zishka and Smith 1980 ), 2
1. Introduction The Madden–Julian oscillation's (MJO; Madden and Julian 1994 ; Zhang 2005 ) convection can initiate and amplify Rossby wave trains ( Matthews et al. 2004 ; Roundy et al. 2010 ; Weare 2010 ) that manifest themselves in teleconnections such as the North Atlantic Oscillation (NAO; Cassou 2008 ; Lin et al. 2009 ) and the Pacific–North American (PNA) patterns ( Kiladis and Weickmann 1992 ; Higgins and Mo 1997 ; Moore et al. 2010 ). The interactions between the MJO and the
1. Introduction The Madden–Julian oscillation's (MJO; Madden and Julian 1994 ; Zhang 2005 ) convection can initiate and amplify Rossby wave trains ( Matthews et al. 2004 ; Roundy et al. 2010 ; Weare 2010 ) that manifest themselves in teleconnections such as the North Atlantic Oscillation (NAO; Cassou 2008 ; Lin et al. 2009 ) and the Pacific–North American (PNA) patterns ( Kiladis and Weickmann 1992 ; Higgins and Mo 1997 ; Moore et al. 2010 ). The interactions between the MJO and the
prominent large-scale circulation modes, such as the North Atlantic Oscillation (NAO; Wallace and Gutzler 1981 ; Barnston and Livezey 1987 ), Pacific–North American (PNA; Wallace and Gutzler 1981 ; Leathers et al. 1991 ) pattern, and El Niño–Southern Oscillation (ENSO; Trenberth 1997 ) have strong influences on temperature and precipitation extremes over different regions. For example, over the contiguous United States, Gershunov and Barnett (1998) examined the signature of ENSO in the wintertime
prominent large-scale circulation modes, such as the North Atlantic Oscillation (NAO; Wallace and Gutzler 1981 ; Barnston and Livezey 1987 ), Pacific–North American (PNA; Wallace and Gutzler 1981 ; Leathers et al. 1991 ) pattern, and El Niño–Southern Oscillation (ENSO; Trenberth 1997 ) have strong influences on temperature and precipitation extremes over different regions. For example, over the contiguous United States, Gershunov and Barnett (1998) examined the signature of ENSO in the wintertime
: Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of transient eddy propagation in the Pacific–North America sector . Quart. J. Roy. Meteor. Soc. , 136 , 277 – 296 , doi: 10.1002/qj.588 . Song , J. , C. Li , W. Zhou , and J. Pan , 2009 : The linkage between the Pacific–North American teleconnection pattern and the North Atlantic Oscillation . Adv. Atmos. Sci. , 26 , 229 – 239 , doi: 10.1007/s00376-009-0229-3 . Strong , C. , and G. Magnusdottir
: Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of transient eddy propagation in the Pacific–North America sector . Quart. J. Roy. Meteor. Soc. , 136 , 277 – 296 , doi: 10.1002/qj.588 . Song , J. , C. Li , W. Zhou , and J. Pan , 2009 : The linkage between the Pacific–North American teleconnection pattern and the North Atlantic Oscillation . Adv. Atmos. Sci. , 26 , 229 – 239 , doi: 10.1007/s00376-009-0229-3 . Strong , C. , and G. Magnusdottir
