An observation-based Southern Hemisphere Annular Mode Index


Methodology

The methodology is essentially the same as outlined in the paper below:

Marshall, G. J., 2003: Trends in the Southern Annular Mode from observations and reanalyses. J. Clim., 16, 4134-4143.

Go here if you have access to online J. Clim. papers.

However, there have been a few subtle changes. Principally, Valdivia has been replaced with Puerto Montt because the former station is no longer operating 24/7. I currently have data for Puerto Montt station for 1960, 11 months of 1961 and then data from April 1967. For missing data a value is calculated using a monthly offset, calculated as the mean for the 1971-2000 period, from the Valdivia data. Efforts are ongoing at the Dirección Meteorológica de Chile to produce accurate monthly data from paper records prior to 1970: much of the early Valdivia data is taken from the World Weather Records dataset, which provides values only to the nearest hPa.

Locations of the 12 stations used to compute zonal means at 40°S and 65°S

Also, the mean values and standard deviations are calculated for the 30-year 1971-2000 period. Thus I am now able to update the time-series when the twelve mean sea level pressure values are available. As I am dependent on other sites to obtain data from some of the extra-tropical stations there is typically a two week lag in producing a monthly value. Note that in some cases I have at present been unable to find all the data: monthly values in blue have one out of six station values missing at one or other of the two latitude bands while those in red have two. In these cases, except for early Puerto Monnt data (see above), the missing value has been calculated using multiple linear regression from the other stations at the appropriate latitude. It is hoped that some of these missing data may be obtained in the future.

Data

      JAN   FEB   MAR   APR   MAY   JUN   JUL   AUG   SEP   OCT   NOV   DEC

1957 -0.87 -2.27  0.07 -1.97 -2.50 -0.87  1.00 -1.73  0.72 -3.12 -5.42 -2.63
1958  0.04 -2.84 -2.52 -0.30 -2.72 -0.97 -1.65  0.97  1.90 -0.16  0.30  0.82
1959  1.59 -0.19 -0.54 -1.25 -0.32 -1.12  0.18 -1.64  2.46 -0.46  3.28 -0.38
1960  0.90  0.85  3.40 -0.35 -0.60 -0.17  0.31  0.43  1.41 -1.17  1.18  1.36
1961  0.91 -4.00 -0.40 -0.14  1.12 -0.40  0.98  1.10 -1.21  1.64  1.52  2.32
1962  2.34 -0.50 -0.66  1.65 -0.66 -3.41  0.33 -0.20 -0.15 -0.36 -2.25  1.35
1963  3.26  1.41  2.03  1.41 -1.09  1.82  0.41 -5.03 -1.59  2.05  1.02 -0.04
1964 -3.29 -1.00 -1.52  0.63  2.38 -4.14 -6.15 -2.26  1.61  0.34 -3.34 -1.49
1965 -0.46 -7.65 -1.58 -0.49 -2.08  1.89  0.08  0.08  0.22  1.91  1.71 -1.48
1966  0.59 -2.94 -2.81 -0.49 -1.66  0.53 -1.65  3.66  0.43  1.30 -1.81 -0.67
1967 -3.42 -4.22  1.09 -0.11 -0.39  2.62  1.22  1.01  1.21  0.64 -2.17 -0.48
1968 -0.07 -1.82 -0.90 -2.72 -2.23 -0.13  1.60  0.25 -0.36 -3.15 -3.36 -0.51
1969 -4.13 -3.14 -0.96 -2.36  1.39 -0.88  1.81  2.10  0.58 -0.35  1.52 -0.41
1970  0.76  1.27 -2.26 -1.57  0.24  0.72 -1.22  1.63 -2.02 -2.19  0.45 -0.72
1971 -0.36  0.16  2.02 -1.24 -2.48  1.31  0.68 -0.78 -1.83 -2.23 -0.50 -1.57
1972 -1.44 -0.36 -2.05 -2.94 -0.09  0.42 -1.24 -1.89 -0.91 -1.48  1.39 -1.38
1973 -0.94  1.39  2.16  0.36 -1.94 -0.12  2.57  1.98 -1.15 -1.28 -0.54  2.17
1974  1.18  1.82  2.81  0.05  0.42  0.08 -1.22 -4.02  1.84 -1.33 -2.24 -2.37
1975 -1.68 -1.22 -1.23  0.56 -3.33 -0.35 -2.42 -0.16  1.23  0.59  0.11  0.35
1976 -1.17  1.02 -0.10  1.56  1.75 -0.01  0.60  0.30  1.67  1.19 -2.88 -5.07
1977 -3.22  0.04 -1.17 -1.36 -0.77 -2.09 -1.82 -0.41  2.69  0.21 -0.20 -0.95
1978  1.50 -0.24 -0.99  0.64 -0.91  0.83 -2.13  2.94  1.19  0.68 -0.96 -0.01
1979  0.74 -0.90  1.51 -0.49  1.54  2.52  3.14  1.39 -0.02  0.54 -1.26 -1.88
1980  0.01 -1.75 -2.58 -1.77 -0.51  3.19 -1.68 -1.68 -2.56  0.45 -2.09 -0.10
1981  0.84  1.76 -2.47 -3.52  0.88  0.38 -1.43 -1.99 -1.49 -0.39  2.34  2.21
1982 -0.77  0.70  4.28  2.89 -0.70  2.40  0.01  1.00  1.56 -2.14 -2.32 -2.21
1983 -2.44  0.89 -0.71 -0.60 -0.68  0.38  1.63  0.09 -0.72  2.05  3.79  1.52
1984 -1.96 -1.74 -0.38 -0.23 -0.33  1.08 -0.21 -2.33 -0.16  1.06  0.34 -3.22
1985 -2.38 -0.02 -0.08  0.95  0.38 -2.49  2.64  1.26  1.07  0.57  2.28  1.90
1986  0.37 -4.89 -1.26 -0.57 -2.19 -0.95 -0.02  1.68  2.72 -0.38  0.50  1.31
1987 -2.51 -2.49 -1.11 -0.17 -0.34  0.18 -0.26  1.79 -0.72  0.78  1.77  0.30
1988  0.13  0.12 -2.01  2.11 -2.03 -3.06  0.64 -2.00 -2.70 -6.03  1.77  1.88
1989 -0.02  1.14  0.20  0.00  3.73  2.91  0.88 -1.21 -0.23 -0.16  0.69 -0.05
1990 -0.23  1.95  0.80 -3.34 -3.35 -0.28 -1.82  0.12  2.08 -0.06  0.29 -0.20
1991  1.50 -1.69  1.07 -1.36  1.02  1.04 -1.56 -0.57 -2.52  1.30 -0.84 -1.23
1992  0.17 -1.89 -1.10  0.53 -2.19 -3.13 -0.80 -0.40  1.06  0.70  1.49  0.58
1993 -2.17  0.77 -0.10  1.80  2.10  0.40  2.82  2.69  1.14  1.21  1.48  1.38
1994  0.53  2.72  1.59 -0.75 -1.50 -2.33 -0.15  1.53 -1.22 -0.47 -2.43  1.91
1995  2.89  0.31 -1.12  0.74  2.64 -0.79 -4.26 -0.51  3.09 -0.69  0.17  1.93
1996  0.55 -1.74  1.31 -0.28  1.90 -1.40  0.22 -2.46 -3.50  2.79 -2.36  0.03
1997  2.37  0.68  1.43  0.15  1.43  0.69  1.82  0.76  0.69 -1.78 -3.17 -0.89
1998  2.65  0.57 -0.05  2.89  1.11  1.31  2.13  2.66  0.74 -0.26  2.84  2.59
1999  2.26  0.56 -1.39  2.44  2.51 -1.81  0.72  1.44  0.16  3.35  1.83  3.12
2000  3.59  2.32  0.74  0.97  1.90 -0.31  0.52 -1.22 -3.20  1.21 -1.32 -2.05
2001  1.43 -2.70 -0.57  3.49 -1.75 -0.02  0.20 -0.15  1.46  1.36  2.54  1.16
2002  2.22  2.80 -4.42  1.60 -1.69 -0.43 -0.67  1.14 -2.18 -5.77  0.03  1.29
2003 -0.52 -0.98 -0.07  2.21  1.04 -2.52  1.20  2.33 -0.99  0.12 -0.15 -0.69
2004  2.56 -3.33  0.74  1.20 -0.15  1.69  2.52  0.00  1.77 -0.59 -1.18 -1.02
2005  1.07  1.59 -0.12  3.46 -0.45 -0.41 -0.50  0.50  0.39 -0.11  0.66 -2.76
2006  0.56 -1.85  1.66 -0.69  2.28  2.05  1.61 -2.64 -0.26  1.79  0.14  1.34
2007  0.03  2.36 -0.77 -0.33 -1.02 -0.65 -2.67 -0.28 -1.88 -0.86  0.03  2.80
2008  2.56  1.09  0.63 -0.81 -0.66  3.00  0.23  0.60  0.46  2.21  1.03  1.01
2009  2.02  0.94  0.50 -0.43 -0.14  0.54 -0.13 -2.44 -0.78  1.47 -1.20  1.09
2010 -0.40 -2.12  0.04  0.08  1.51  3.14  3.37  1.24 -0.33  3.19  3.88  0.25
2011  0.48  0.87 -0.79  1.62  1.37  0.72 -1.52 -0.73 -1.79  0.59 -1.41  3.43
2012  3.08 -1.53  0.48  2.18  0.47  1.46  3.18  1.34  0.09  0.83 -0.84 -0.90
2013  0.71  2.84  2.31 -0.07  0.88  0.23  1.17 -3.25 -2.72 -1.39  1.07  0.77
2014 -0.13  0.36  1.34  1.18 -1.62 -0.21  0.68  1.97 -1.62  1.32  0.35

Access monthly data in ASCII format

Annual and seasonal data

These have been calculated using the mean zonal mean sea level pressure for the year or season to derive the SAM rather than simply the mean of the monthly SAM values. Note that for summer (DJF) the year refers to the December.

Access annual and seasonal data in ASCII format

Figures

Month by month: the thick line is a 12-month running mean.

Annual and seasonal data: the thick line is the annual data.

Updated version of Figure 3.32 in the IPCC AR4 Climate Change 2007: The Physical Science Basis.

Calendar year

Autumn (MAM)

Winter (JJA)

Spring (SON)

Summer (DJF)

Comments should be addressed to Dr Gareth Marshall at GJMA@bas.ac.uk.