Extratropical Highlights –January 2016
1. Northern Hemisphere
The 500-hPa circulation during January
featured above-average heights across the polar region and across both the
subtropical North Pacific and Atlantic Oceans and Africa. The circulation also
featured below-average heights across the central North Pacific and Atlantic
Oceans and Europe (Fig. E9). This overall anomaly pattern projected strongly
onto the positive phase of the Pacific/ North American teleconnection pattern (PNA,
+1.9) and also onto the negative phase of the Polar/ Eurasia Pattern (-2.6) (Table E1., Fig. E7). A
positive PNA pattern is a typical response to El Niño.
At 200-hPa, a significant El Niño
response continued in the streamfunction (Fig.
T22) and wind (Figs. T21) fields. This response featured anticyclonic anomalies over
the eastern half of the subtropical North and South Pacific, straddling the
region of enhanced convection (Fig. T25), along with cyclonic anomalies at higher latitudes of the North Pacific.
This pattern was associated with an eastward extension of the wintertime East
Asian jet steam to well east of the date line. This jet stream pattern
represents major dynamical and kinematic changes in the mid- and upper-level
circulation during El Niño, and it also represents a fundamental manner in
which El Niño’s circulation impacts are communicated downstream.
The main land-surface temperature signals
during January included above-average temperatures across Canada, western Europe, and eastern Siberia (Fig. E1). The main precipitation signals
included above-average totals in the northwestern U.S., the Gulf Coast region
of the U.S., western Europe, and eastern China. Below-average
totals were recorded across central U.S. and north-central Russia (Fig. E3).
a. North Pacific/ North America
At 500-hPa, the circulation during January
featured above-average heights across the subtropical North Pacific Ocean and western
Canada, and below-average heights over the central and high latitudes of the
North Pacific and the southeastern U.S. (Fig.
E9). At 200-hPa, the circulation featured
anticyclonic streamfunction anomalies across the subtropical eastern North
Pacific in association with El Niño, along with negative anomalies over the
high latitudes of the North Pacific (Fig.
T22). This pattern was associated
with an eastward extension of the wintertime East Asian jet steam to well east
of the date line. It was also associated with enhanced westerly winds
throughout the troposphere in the western U.S. (Figs. T20, T21). These conditions reflected a
strong positive PNA pattern and contributed to increased storminess in the
western U.S., both of which are typical of El Niño.
This circulation contributed to anomalously
warm surface temperature across most of Canada, with many areas again recording
departures in excess of +5oC and in the upper 90th
percentile of occurrences (Fig. E1). It also contributed to above-average
precipitation in the northwestern and Gulf Coast regions of the U.S., and to
below-average precipitation in the central U.S. (Fig. E3).
According to the U.S. Drought
Monitor, drought conditions were lessened in Washington, Oregon, and Idaho,
while exceptional drought continued across central California and western
Nevada. Severe drought persisted in south-central and eastern Oregon, while
extreme drought persisted in western Montana.
b. North Atlantic
The 500-hPa circulation during January
featured above-average heights over northern Africa and below-average heights across
the eastern North Atlantic and Europe. These conditions were associated with an
exceptionally strong southwesterly flow of jet stream winds and low-level winds
into western Europe, which resulted in anomalously
warm and wet conditions in the region (Figs.
E1, E3, E4).
Well above-average precipitation
was recorded in eastern China during January (Fig. E3), with totals reaching near-record levels (1971-present record)
for the third straight month (Fig. E4). The
continued surplus precipitation was again linked to an amplified 200-hPa trough
over China (Fig. T22).
2. Southern Hemisphere
The mean 500-hPa circulation during
January featured above-average heights south of Australia, south of Africa, and
over the high latitudes of the eastern South Pacific. The circulation also featured
below-average heights over the central South Pacific and throughout the polar
region (Fig. E15).
At 200-hPa, a significant El Niño response was evident in the ongoing pattern
of anticyclonic streamfunction anomalies across the eastern half of the South Pacific
Ocean (Fig. T22).
The main precipitation signals during
January included above-average totals across southern Australia, with
departures exceeding the 90th percentile of occurrences in both the
southwest and southeast (Fig. E3).
Consistent with El Niño, below-average
precipitation was again observed in the South African monsoon region (Fig. E4). The
South African rainy season lasts from October to April. To date, the region has
received well below-average precipitation in every month from October-January.