65
Figure 23: As in tbe bottom panel of Fig. 19, but for rainfall (repeated from Fig. 21)
and vertically averaged (surface to 300-mb) tropospberic temperature as inferred from
cbannel 2 of tbe microwave sounding unit. Heavy sbading denotes enbanced rainfall,
ligbter sbading reduced rainfall. Contour interval 0.1 K per standard deviation of tbe
cold tongue index: dasbed contours denote negative values.
both hemispheres, along the poleward flanks of the dipole pattern over the
eastern Pacific. The anomalous strengthening of the westerlies in these
regions during the warm phase of the ENSO cycle is reflected in increased
storminess over the southern United States and the corresponding latitude
belt of South America (Ropelewski and Halpert 1989).
The MSU tropospheric temperature record, upon which Figure 23 is
based, extends back only to the beginning of 1979. Figure 24 shows the
corresponding pattern for the Northern Hemisphere wintertime 500-mb
height field, based on data extending back to 1946. Unlike the previous
figures, it is based upon data for the Northern Hemisphere winter (December through February) when the relationships between the tropical
and extratropical circulation tend to be strongest. The typical pattern
of ENSO anomalies bears some relation to the PN A pattern discussed in
section 4, but the region of positive anomalies over Canada extends farther eastward, and the region of negative anomalies over the North Pacific
stretches northwestward toward Kamchatka rather than westward along
45 ON. The positive anomalies over Canada provide an explanation of the
finding of Walker and Bliss (193:2) that winters over western Canada tend
Figure 23: As in tbe bottom panel of Fig. 19, but for rainfall (repeated from Fig. 21)
and vertically averaged (surface to 300-mb) tropospberic temperature as inferred from
cbannel 2 of tbe microwave sounding unit. Heavy sbading denotes enbanced rainfall,
ligbter sbading reduced rainfall. Contour interval 0.1 K per standard deviation of tbe
cold tongue index: dasbed contours denote negative values.
both hemispheres, along the poleward flanks of the dipole pattern over the
eastern Pacific. The anomalous strengthening of the westerlies in these
regions during the warm phase of the ENSO cycle is reflected in increased
storminess over the southern United States and the corresponding latitude
belt of South America (Ropelewski and Halpert 1989).
The MSU tropospheric temperature record, upon which Figure 23 is
based, extends back only to the beginning of 1979. Figure 24 shows the
corresponding pattern for the Northern Hemisphere wintertime 500-mb
height field, based on data extending back to 1946. Unlike the previous
figures, it is based upon data for the Northern Hemisphere winter (December through February) when the relationships between the tropical
and extratropical circulation tend to be strongest. The typical pattern
of ENSO anomalies bears some relation to the PN A pattern discussed in
section 4, but the region of positive anomalies over Canada extends farther eastward, and the region of negative anomalies over the North Pacific
stretches northwestward toward Kamchatka rather than westward along
45 ON. The positive anomalies over Canada provide an explanation of the
finding of Walker and Bliss (193:2) that winters over western Canada tend