Ferrell pressure 1981 - 987.7 989.7 992.5 984.9 978.6 987.0 995.2 988.7 980.9 977.1 978.6 1982 989.8 986.5 977.9 980.1 986.7 980.1 989.2 975.3 976.4 980.1 984.5 994.5 1983 992.0 994.7 985.1 979.4 985.5 989.0 981.2 - - - - - 1984 993.9 989.0 979.3 980.0 987.7 980.6 975.8 985.7 981.0 - - - 1985 - 988.8 987.0 987.9 - - 975.6 986.1 976.0 976.9 - - 1986 - 993.5 991.9 981.5 992.3 992.0 981.3 984.3 979.6 974.2 976.0 981.7 1987 - 988.7 987.7 989.8 984.1 988.7 993.7 976.4 989.5 980.3 979.2 985.9 1988 988.8 985.4 986.6 984.6 990.9 995.5 - 975.9 984.8 990.7 981.4 982.5 1989 984.8 985.7 984.9 - - - - - - 975.9 976.0 988.9 1990 988.5 983.1 987.1 993.6 999.5 989.5 999.2 982.6 974.3 983.1 984.7 984.8 1991 983.7 989.8 983.6 988.3 989.3 992.3 - - - - 984.8 995.4 1992 989.0 997.7 988.4 987.2 992.9 996.8 984.8 - - - - - 1993 - 977.9 985.6 981.4 983.0 976.3 972.2 978.3 976.7 976.2 979.0 982.4 1994 984.0 982.6 978.6 985.5 985.1 998.7 989.2 975.0 989.4 977.6 983.9 980.1 1995 980.1 981.0 990.9 983.6 981.0 988.4 1001.5 986.4 977.9 979.9 977.4 977.2 1996 985.5 990.2 985.2 978.7 985.8 982.4 982.6 987.5 989.3 972.2 986.8 985.0 1997 988.4 989.4 980.1 986.0 973.4 987.6 979.9 977.8 981.0 976.8 986.9 990.2 1998 985.4 980.6 982.1 976.2 982.7 977.5 980.7 - - - - - 1999 - 987.3 - - - - - - - - - - 2000 - - - - - - - - - - - - 2001 - 988.2 985.5 979.6 985.3 982.2 987.2 983.6 979.3 972.5 976.0 976.4 2002 983.2 977.9 990.4 981.2 992.1 995.0 989.4 979.2 986.6 989.8 983.5 978.7 2003 - - - - - - - - - - - - 2004 - - - - - - - - - - - - 2005 - - - - - - - - - - - - 2006 - - - - - - - - - - 978.6 982.9 2007 986.2 983.0 989.9 984.8 986.8 985.8 997.0 979.4 978.1 982.2 981.7 975.6 2008 979.9 979.9 984.7 985.7 983.7 977.0 980.3 982.7 972.1 974.0 - - 2009 - - - - - - - - - - - -