2. Factors Controlling the Climate of the West Coast of North America 35
British Columbia coast, height decreases downstream over central North
America and other areas (that are different for the north and south
coastal regions). For each case, there are significant changes quite distant
from British Columbia; these may indicate large-scale flow anomalies or
just be statistical noise.
Role of Sea-Surface Temperature Patterns over
the North Pacific Ocean
It has been noted that there were some long-period variations to both the
precipitation anomalies and the atmospheric flow indices. For example,
anomalies of coastal precipitation tended to be negative from the late
1940s until 1958. The question is, what is the cause of these long-period
variations in the atmospheric flow and the precipitation? Since the
atmosphere has a relatively short memory or adjustment time (a month
or less), it seems likely that these long-period variations are linked to
variations in the ocean. Correlations between the sea-surface temperature
(SST) anomalies and the regional time-series anomalies and standardized
anomaly indices for precipitation time series, separating the data into
winter and summer half-years, were generally quite small (McBean &
Hourston, 1994).
In a review of all composite SST anomaly plots for standardized
anomaly indices for precipitation, two anomaly patterns emerge consistently for summer and winter. The summer pattern is characterized by
two regions of significant SST anomalies of the same sign in the northwest
and northeast Pacific. The winter recurring anomaly pattern is characterized by two regions of significant SST anomalies of different signs in
the northeast Pacific near 30°Nand 50°N. Persistence of these SST
anomaly patterns over the given season for indices based on precipitation
over a large area lends support to the idea that these large-scale SST
anomalies are associated with large-scale precipitation anomalies over
British Columbia. In the case of the second (winter) pattern, the largescale positive SST anomaly region near 30°N covers most of the North
Pacific, and this anomalous heat source may serve to increase the energy
and moisture content for cyclones moving east over the Pacific, resulting
in larger precipitation amounts over British Columbia. The dynamics of
this relation (and for the first, or summer pattern) are not clear, however,
but this analysis suggests that they warrant further investigation. Emery
and Hamilton (1985) and others have investigated the relationship between the EI Nino and the interannual variability of the northeast Pacific
Ocean and found that although there were general tendencies for seasurface temperature to be anomalously high during EI Nino events, the
lack of a " truly predictable relation" points out that other factors are also
important.
British Columbia coast, height decreases downstream over central North
America and other areas (that are different for the north and south
coastal regions). For each case, there are significant changes quite distant
from British Columbia; these may indicate large-scale flow anomalies or
just be statistical noise.
Role of Sea-Surface Temperature Patterns over
the North Pacific Ocean
It has been noted that there were some long-period variations to both the
precipitation anomalies and the atmospheric flow indices. For example,
anomalies of coastal precipitation tended to be negative from the late
1940s until 1958. The question is, what is the cause of these long-period
variations in the atmospheric flow and the precipitation? Since the
atmosphere has a relatively short memory or adjustment time (a month
or less), it seems likely that these long-period variations are linked to
variations in the ocean. Correlations between the sea-surface temperature
(SST) anomalies and the regional time-series anomalies and standardized
anomaly indices for precipitation time series, separating the data into
winter and summer half-years, were generally quite small (McBean &
Hourston, 1994).
In a review of all composite SST anomaly plots for standardized
anomaly indices for precipitation, two anomaly patterns emerge consistently for summer and winter. The summer pattern is characterized by
two regions of significant SST anomalies of the same sign in the northwest
and northeast Pacific. The winter recurring anomaly pattern is characterized by two regions of significant SST anomalies of different signs in
the northeast Pacific near 30°Nand 50°N. Persistence of these SST
anomaly patterns over the given season for indices based on precipitation
over a large area lends support to the idea that these large-scale SST
anomalies are associated with large-scale precipitation anomalies over
British Columbia. In the case of the second (winter) pattern, the largescale positive SST anomaly region near 30°N covers most of the North
Pacific, and this anomalous heat source may serve to increase the energy
and moisture content for cyclones moving east over the Pacific, resulting
in larger precipitation amounts over British Columbia. The dynamics of
this relation (and for the first, or summer pattern) are not clear, however,
but this analysis suggests that they warrant further investigation. Emery
and Hamilton (1985) and others have investigated the relationship between the EI Nino and the interannual variability of the northeast Pacific
Ocean and found that although there were general tendencies for seasurface temperature to be anomalously high during EI Nino events, the
lack of a " truly predictable relation" points out that other factors are also
important.