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General Notes
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Modes of Variability
ENSO Spatial Composites | El Niño (La Niña) events are defined based on the December value of the Nino34 SST Index (smoothed with a 3-point binomial filter) greater than or equal to 1 (less than or equal to -1) standard deviation. The number of El Niño/La Niña events composited is indicated in the subtitle located to the upper right of each panel. TS/TAS/PSL composites: Temperatures are color shaded and in units of Celsius. Sea level pressure is contoured from -16 to 16hPa by 2hPa; negative contours are dashed. PR composites: Precipitation is color shaded and is in units of mm/day. See Deser, C., A. S. Phillips, R. A. Tomas, Y. Okumura, M. A. Alexander, A. Capotondi, J. D. Scott, Y. -O. Kwon, and M. Ohba (2012), ENSO and Pacific Decadal Variability in Community Climate System Model Version 4. Journal of Climate, 25, 2622-2651, doi: 10.1175/JCLI-D-11-00301.1. |
El Niño and La Niña Hovmöllers | El Niño (La Niña) events are defined based on the December value of the Nino34 SST Index (smoothed with a 3-point binomial filter) greater than or equal to 1 (less than or equal to -1) standard deviation. The number of El Niño/La Niña events composited is indicated in the subtitle located to the upper right of each panel. Meridional averages are calculated by averaging from 3°S:3°N, and spatial patterns are formed by compositing from Jan year 0 to May year 2. See Deser, C., A. S. Phillips, R. A. Tomas, Y. Okumura, M. A. Alexander, A. Capotondi, J. D. Scott, Y. -O. Kwon, and M. Ohba (2012), ENSO and Pacific Decadal Variability in Community Climate System Model Version 4. Journal of Climate, 25, 2622-2651, doi: 10.1175/JCLI-D-11-00301.1. |
PDV (Pacific Decadal Variability) | Monthly index timeseries defined as the leading principal component (PC) of North Pacific (20:70°N, 110°E:100°W) area-weighted SST anomalies. Pattern created by regressing SST anomalies (in Celsius) at each grid box onto the normalized PC timeseries. Low pass-filtered timeseries (black curve) is based on a 61-month running mean. See Deser, C., M. A. Alexander, S. -P. Xie, and A. S. Phillips (2010), Sea surface temperature variability: patterns and mechanisms. Ann. Rev. Mar. Sci., 2010.2, 115-143, doi:10.1146/annurev-marine-120408-151453. Also see Mantua, N. J., S. R. Hare, Y. Zhang, J. M. Wallace, and R. Francis (1997), A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Amer. Met. Soc., 1069-1079. For more information on the PDV see the Climate Data Guide. |
IPV (Standard) (Interdecadal Pacific Variability) | Monthly index timeseries defined as the leading principal component (PC) of 13yr low pass filtered Pacific (40°S:60°N, 110°E:70°W) area-weighted SST anomalies. Pattern created by regressing SST anomalies (in Celsius) at each grid box onto the normalized PC timeseries. At least 40 years of data are required for the standard IPV index to be calculated. See Meehl, G.A. and A. Hu (2007), Megadroughts in the Indian Monsoon Region and Southwest North America and a Mechanism for Associated Multidecadal Pacific Sea Surface Temperature Anomalies, Journal of Climate, 19, 1605-1623, doi: 10.1175/JCLI3675.1. |
IPV (Henley) (Interdecadal Pacific Variability) | Monthly index timeseries defined as the area-weighted SST anomalies averaged over the central tropical Pacific (10°S:10°N, 170°E:90°W) minus the average of the area-weighted SST anomalies averaged over the north (25°:45°N, 140°E:145°W) and south (15°:50°S, 150°E:160°W) Pacific. Pattern created by regressing SST anomalies (in Celsius) at each grid box onto the timeseries. See Henley, B.J., J. Gergis, D.J. Karoly, S. Power, J. Kennedy and C.K. Folland (2015), A Tripole Index for the Interdecadal Pacific Oscillation, Clim. Dyn., 45, 3077-3090, doi: 10.1007/s00382-015-2525-1. |
AMV (Atlantic Multidecadal Variability) | Monthly index timeseries defined as area-weighted SST anomalies averaged over the North Atlantic (0:60°N, 80°W:0°E). Pattern created by regressing SST anomalies onto the index timeseries and smoothing with a 9-point spatial filter. Low pass-filtered timeseries (black curve superimposed on the monthly timeseries) is based on a 61-month running mean. Low-pass filtered regression maps ("Regr LP") use a 10-year running mean on both the index timeseries and the field being regressed. For more information on the definition of AMV in a changing background climate, see Deser C. and A. S. Phillips (2023), Spurious Indo-Pacific connections to internal Atlantic Multidecadal Variability introduced by the global temperature residual method. Geophys. Res. Lett., 50, e2022GL100574, doi: 10.1029/2022GL100574. For more information on the AMV see the Climate Data Guide. |
AMOC | The Atlantic Meridional Overturning Circulation (AMOC) is defined as the leading Principal Component (PC) time series of annual mean oceanic meridional mass transport (Sv) in the Atlantic sector (33°S-90°N) following Danabasoglu et al. (2012). Here we use annual averages instead of monthly values. The AMOC patterns are created by regressing the AMOC anomalies (in Sv) onto the normalized PC timeseries. The SST/TAS patterns are created by regressing TAS/SST anomalies (in Celsius) at each grid box over the globe onto the normalized AMOC PC timeseries. A 15-point low-pass Lanczos filter is applied to the AMOC PC (and AMV) timeseries prior to computing lead/lag correlations, with a minimum of 90 years of data required. See Danabasoglu, G., S. G. Yeager, Y. -O. Kwon, J. J. Tribbia, A. S. Phillips, and J. W. Hurrell (2012), Variability of the Atlantic Meridional Overturning Circulation in CCSM4. J. Climate, 25, 5153-5172, doi: 10.1175/JCLI-D-11-00463.1. For CCSM4 and CESM1, the MOC variable is read in, the Eulerian Mean, Eddy-Induced and Submeso components are summed, and the Atlantic Ocean + Mediterranean Sea + Labrador Sea + GIN Sea + Arctic Ocean + Hudson Bay transport region is selected. For CCSM2 and CCSM3 the same transport region is selected but only the Eulerian Mean component is used as that is all that is available. For CMIP5 (CMIP6) data the msftmyz (msftmz) variable is read in and the atlantic_arctic_ocean basin is used. For CMIP3 data, the stfmmc variable is read in and the atlantic_ocean geo_region is used. |
SO | The Southern Oscillation Index is defined as the difference between area-averaged PSL anomalies (in hPa) computed over 30°S:0°N, 70:170°E and area-averaged PSL anomalies computed over 30°S:0°N, 160:80°W. Pattern created by regressing global PSL anomalies (in hPa) onto the timeseries. See Deser, C. and J. M. Wallace (1990), Large-scale atmospheric circulation features of warm and cold episodes in the Tropical Pacific. J. Climate, 3, 1254-1281, doi: 10.1175/1520-0442(1990)003<1254:LSACFO>2.0.CO;2. |
NAM (Northern Annular Mode) | Seasonal/annual PSL averages are formed, square root of the cosine of the latitude weighting is applied, and then the leading EOF and associated principal component (PC) timeseries are computed over 20:90°N, 0:360°E. Pattern created by regressing global PSL anomalies (in hPa) onto normalized PC timeseries. Based on Hurrell, J. W., and C. Deser (2009), North Atlantic climate variability: The role of the North Atlantic Oscillation. J. Mar. Syst., 78, 28-41, doi:10.1016/j.jmarsys.2008.11.026. Also see Thompson, D. W. J., and J. M. Wallace, 2000: Annular modes in the extratropical circulation. Part I: Month-to-month variability. Journal of Climate, 13, 1000-1016. |
NAO (North Atlantic Oscillation) | Seasonal/annual PSL averages are formed, square root of the cosine of latitude weighting is applied, and then the leading EOF and associated principal component (PC) timeseries are computed over 20:80°N, 90°W:40°E. Pattern created by regressing global PSL anomalies (in hPa) onto normalized PC timeseries. Based on Hurrell, J. W. and C. Deser (2009), North Atlantic climate variability: The role of the North Atlantic Oscillation. J. Mar. Syst., 78, 28-41, doi:10.1016/j.jmarsys.2008.11.026. For more information on the NAO see the Climate Data Guide. |
SAM/PSA1/PSA2 (Southern Annular Mode, Pacific South American Patterns 1/2) | Seasonal/annual PSL averages are formed, square root of the cosine of latitude weighting is applied, and then the 1st (SAM), 2nd (PSA1) and 3rd (PSA2) EOFs and associated principal component (PC) timeseries are computed over 20:90°S, 0:360°E. Patterns created by regressing global PSL anomalies (in hPa) onto normalized PC timeseries. SAM calculation based on Thompson, D. W. J. and J.M. Wallace, (2000), Annular modes in the extratropical circulation. Part I: Month-to-month variability. Journal of Climate, 13, 1000-1016. |
PNA/NPO (Pacific North American Pattern, North Pacific Oscillation) | Seasonal/annual PSL averages are formed, the square root of the cosine of the latitude weighting is applied, and then the 1st (PNA) and 2nd (NPO) EOFs and associated principal component (PC) timeseries are computed over 20:85°N, 120°E:120°W. Patterns created by regressing global PSL anomalies (in hPa) onto normalized PC timeseries. |
Climate Indices
Atlantic SST Meridional Mode | Defined as the difference between area-averaged SST anomalies (in Celsius) computed over 5:15°N, 20:50°W and area-averaged SST anomalies computed over 5:15°S, 20°W:10°E. See Doi, T., T. Tozuka and T. Yamagata (2009), Interannual variability of the Guinea Dome and its possible link with the Atlantic Meridional Mode. Climate Dynamics, 33, 985-998, doi:10.1007/s00382-009-0574-z. |
Atlantic Niño SST | Area-averaged SST anomalies (in Celsius) computed over 3°S:3°N, 20°W:0°E. See Zebiak, S. E. (1993), Air–sea interaction in the equatorial Atlantic region. Journal of Climate, 6, 1567–1586. |
North Atlantic SST | Area-averaged SST anomalies (in Celsius) computed over 0°:60°N, 90°W:0°E. |
Tropical North Atlantic SST | Area-averaged SST anomalies (in Celsius) computed over 5.5:23.5°N, 15:57.5°W. See Enfield, D.B., A.M. Mestas, D.A. Mayer, and L. Cid-Serrano (1999), How ubiquitous is the dipole relationship in tropical Atlantic sea surface temperatures?, JGR-O, 104, 7841-7848. |
Tropical South Atlantic SST | Area-averaged SST anomalies (in Celsius) computed over 0:20°S, 30°W:10°E. See Enfield, D.B., A.M. Mestas, D.A. Mayer, and L. Cid-Serrano (1999), How ubiquitous is the dipole relationship in tropical Atlantic sea surface temperatures?, JGR-O, 104, 7841-7848. |
niño1+2 | Area-averaged SST anomalies (in Celsius) computed over 0:10°S, 80:90°W. |
niño3 | Area-averaged SST anomalies (in Celsius) computed over 5°S:5°N, 90:150°W. See Rasmusson E. M. and T. H. Carpenter (1982), Variations in Tropical Sea Surface Temperature and Surface Wind Fields Associated with the Southern Oscillation/El Niño, Monthly Weather Review, 110, 354 – 384, https://doi.org/10.1175/1520-0493(1982)110<0354:VITSST>2.0.CO;2. |
niño3.4 | Area-averaged SST anomalies (in Celsius) computed over 5°S:5°N, 120:170°W. See Rasmusson E. M. and T. H. Carpenter (1982), Variations in Tropical Sea Surface Temperature and Surface Wind Fields Associated with the Southern Oscillation/El Niño, Monthly Weather Review, 110, 354 – 384, https://doi.org/10.1175/1520-0493(1982)110<0354:VITSST>2.0.CO;2. |
niño4 | Area-averaged SST anomalies (in Celsius) computed over 5°S:5°N, 160°E:150°W. |
NPI (North Pacific PSL Index) | Winter (December-March) average PSL anomalies (in hPa) area-averaged over 30°:65°N, 160°E:140°W. Based on Trenberth, K. E. and J. W. Hurrell (1994), Decadal atmosphere-ocean variations in the Pacific, Climate Dynamics, 9, 303-319. |
North Pacific Meridional Mode | See Chiang, J. C. H. and D. J. Vimont (2004), Analogous Pacific and Atlantic Meridional Modes of Tropical Atmosphere–Ocean Variability. Journal of Climate, 17, 4143–4158, doi: 10.1175/jcli4953.1. |
South Pacific Meridional Mode | See Zhang, H., A. Clement and P. Di Nezio (2014), The South Pacific Meridional Mode: A Mechanism for ENSO-like Variability. Journal of Climate, 27, 769–783, doi: 10.1175/jcli-d-13-00082.1. |
Indian Ocean SST Dipole | Defined as the difference between area-averaged SST anomalies (in Celsius) computed over 10°S:10°N, 50:70°E and area-averaged SST anomalies computed over 0:10°S, 90:110°E. See: Saji, N.H., B. N. Goswami, P. N. Vinayachandran, and T. Yamagata (1999), A dipole mode in the tropical Indian Ocean, Nature, 401, 360-363. |
Tropical Indian Ocean SST | Area-averaged SST anomalies (in Celsius) computed over 15°S:15°N, 40:110°E. |
Southern Ocean SST | Area-averaged SST anomalies (in Celsius) computed over 50°:70°S, 0:360°E. |
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