The following indices are generated by projecting various anomaly fields onto the structure of the "AO",
defined here as the leading EOF of SLP poleward of 20N based on all months
Jan1958 to April1997. All units are arbitrary.
AO_Daily_Index_1958Current.ascii
AO_index_NCEP_Jan1958May2000.ascii
AO_TREN_NCEP_Jan1899May2000.ascii
AO_SATindex_JFM_Jan1851March1997.ascii
MONTHLY INDEX BASED ON SAT DATA. January-March monthly-mean values from Jan1851 to March1997.
The first column is the time axis in years (and
fractions of years: i.e. 1958+0/3 would be Jan 1958, 1958+2/3 is March 1958, etc).
The second column is the index values. In this case the index values are the expansion coefficient
time series of the pattern of SAT anomalies associated with the AO (see Thompson and Wallace 1998, and
Thompson et al. 1999). SAT data provided by P. D. Jones (Jones 1994) from the CRU.
AAO_index_NCEP_Jan1958Mar2000.ascii
References:
Thompson, David W. J. and John. M. Wallace, 2000: Annular modes in the extratropical circulation. Part I: Month-to-month variability. J. Climate, 13, 1000-1016.
Thompson, David W. J., John. M. Wallace, and Gabriele C. Hegerl, 2000: Annular modes in the extratropical circulation. Part II: Trends. J. Climate, 13, 1018-1036. Please address any questions about the analysis or the above papers
to David W. J. Thompson davet@atmos.colostate.edu
"Real time" DAILY INDEX BASED ON NCEP/NCAR REANALYSIS. Index values are found by projecting the structure of EOF1 of NH SLP (see Thompson and Wallace 2000) onto daily SLP anomalies. Index values start Jan 1 1958, end at current date (updated weekly).
Figure available through this link.
MONTHLY INDEX 1958-May 2000 BASED ON NCEP/NCAR REANALYSIS. EOF is computed from data for all months, 1958-1997. Index values after 1997 are found by projecting the structure of the EOF onto monthly SLP anomalies. Index starts Jan1958, ends May 2000. Units are arbitrary.
MONTHLY INDEX Jan1899 to May2000. Found by projecting the AO pattern
onto SLP anomalies back to Jan 1899. Index starts Jan 1899, ends May 2000.
Index values 1899-Dec1957 are based on data described in Trenberth and Paolino (1980). Index values Jan1958 to current are from the NCEP/NCAR Reanalysis.
Index of the SH annular mode based on PC1 of the 850-hPa height field, 20-90S, from the NCEP/NCAR Reanalysis. EOF is computed for data from all months, 1958-1997. Index values after 1997 are found by projecting the structure of the EOF onto monthly 850Z anomalies. Index starts Jan1958, ends March 2000. Units are arbitrary. NOTE THAT THE TREND IN THE INDEX MAY CONTRIBUTE TO "SPURIOUS" CORRELATIONS.
Thompson, David W. J. and John. M. Wallace, 1998: The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25, No. 9, 1297-1300.
Postscript file of the manuscript and color figures
Postscipt file (provided by the AMS)
Postscript file (provided by the AMS)