Recent Atmospheric and Oceanic Circulation Changes Affecting Winter Weather in North America. Dr. Art Douglas Professor Emeritus Creighton University

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1 Recent Atmospheric and Oceanic Circulation Changes Affecting Winter Weather in North America Dr. Art Douglas Professor Emeritus Creighton University

2 Outline 1. The 2018 El Nino: A Northern Hemisphere induced event opposed by Southern Hemisphere circulation. The Antarctic ozone hole may have been suppressing El Nino activity since The Northwest Atlantic Warm Pool : Changes in the effect of this warm pool vs Major adjustments in North America circulation and climate have occurred since The Gulf of Alaska Warm Pool: Typically associated with El Nino and expected impacts on winter temperatures and precipitation in North America.

SST Anomalies in Regions of Discussion November 22, 2018 El Nino warming extends from the Dateline to the coast of Peru. Anomalies are approaching levels associated with a moderate El Nino event.

3 SST Anomalies in Regions of Discussion November 22, 2018 El Nino warming extends from the Dateline to the coast of Peru. Anomalies are approaching levels associated with a moderate El Nino event. Warm waters in the Pacific south of Hawaii will drive a strong Subtropical Jetstream towards the U.S. while the temperature gradient in the North Atlantic will strengthen the Polar Jetstream in the eastern U.S.

4 NOAA and ECMWF El Nino Forecasts through Summer 2019 The most recent runs of the CFSv2 (blue lines upper graph) indicate the warming event will peak in December near +1.2C. The ECMWF forecast issued on November 1 st is similar to the NOAA model. Both models show a second warming phase in April which will keep spring storms across the plains. There is no indication that La Nina will develop this summer so wet weather should persist in the corn belt into the summer. NOAA CFSv2 Nov ECMWF Nov

5 Internal Ocean Wave Moving East Towards Peru An internal ocean wave in the West Pacific is moving towards Peru. The wave was release with the weakened trade winds off South America and a burst of westerly wind coming into the Pacific from the Indian Ocean. Warm water off Peru is associated with the weakened trade winds during October and early November. El Nino is in place. SE ASIA Dateline PERU SE ASIA Dateline PERU

6 The NOAA CFSv2 forecast of Equatorial Ocean Temperatures from the Surface to 300m through August 2019 The NOAA model shows the internal ocean wave gradually shifting to the coast off South America (S.A.) through June. The wave and associated temperature anomalies weaken as the wave moves to the coast of Peru. NOV AFR EASIA S.A. AFR SEASIA S.A. AFR SEASIA S.A. DEC MAR JUN AUG

7 The Cross Equatorial Flow Index (CEFI) The CEFI index measures the pressure gradient between Easter Island and Liberia in Costa Rica. From early October to early November the index fell indicating Pacific Trade Winds were weakening allowing El Nino to build. The most recent NOAA shows the observed warming and additional warming into December Difference (mb)20 Pressure Difference Easter Island Minus Liberia, Costa Rica NOAA CFSv2 forecast Nino 1&2 off Peru La Nina Develops >12mb El Nino Develops <8mb AUG Date NOV

8 MARCH NINO 3.4 JULY NINO 3.4 MAY NINO 3.4 AUGUST NINO 3.4

9 NINO 1&2 AUG-DEC SST ANOMALIES Despite recent strong El Nino events in 1997 and 2015, SSTs off Peru appear to have shifted to a cooler regime between El Nino events. The cooler regime is due to a stronger South Pacific anticyclone forced from a strong Antarctic circumpolar vortex. The vortex has been enhanced by the ozone hole over the Antarctica.

The 5mb September-October Temperature Anomalies 2000-2018 minus 1950-1980 In the Southern Hemisphere spring the stratosphere has shown strong warming from 2000-2018 in

10 The 5mb September-October Temperature Anomalies minus In the Southern Hemisphere spring the stratosphere has shown strong warming from in comparison with This warming is tied to the Ozone Hole. Below the warm Stratospheric anomaly a strong 700mb trough has been favored surrounding the Antarctic Ice cap.

The September-October 700mb Height Anomalies 2000-2018 vs. 1950-1980 In the Southern Hemisphere spring a deep 700mb trough has been favored 2000-18.

11 The September-October 700mb Height Anomalies vs In the Southern Hemisphere spring a deep 700mb trough has been favored This appears to be a direct result of the warming at 5mb. The strong westerlies to the north of the Antarctic trough have built an intensified South Pacific High through anticyclonic turning north of the westerlies. A strong surface high has formed below the 700mb ridge.

The September-October Sea Level Pressure Anomalies 2000-2018 vs. 1950-1980 In the Southern Hemisphere spring a deep surface trough has been favored 2000-18.

12 The September-October Sea Level Pressure Anomalies vs In the Southern Hemisphere spring a deep surface trough has been favored This appears to be a direct result of the warming at 5mb which has induced troughing at 700mb. The strong westerlies to the north of the Antarctic trough have built an intensified South Pacific High through anticyclonic turning north of the westerlies. A strong surface high has formed below the 700mb ridge.

Change in Surface Precipitation From Low Ozone Period 1950-80

and increased zonal circulation in the Southern Hemisphere,

13 Change in Surface Precipitation From Low Ozone Period vs. High Ozone Period With the stronger ozone hole and increased zonal circulation in the Southern Hemisphere, cross equatorial flow has been enhanced into the ITCZ south of Mexico.

14 SST Anomalies in Regions of Discussion November 22, 2018 El Nino warming extends from the Dateline to the coast of Peru. Anomalies are approaching levels associated with a moderate El Nino event. Warm waters in the Pacific south of Hawaii will drive a strong Subtropical Jetstream towards the U.S. while the temperature gradient in the North Atlantic will strengthen the Polar Jetstream in the eastern U.S.

15 X NORTHWEST ATLANCTIC SSTS Current SSTs in the Northwest Atlantic continue near record highs How have warming events in the Northwest Atlantic changed since the world shift in SSTs in 1997? NOV. SSTs

The 2000-2018 SST Response to Warm Episodes in the Northwest Atlantic Warm phases in the Northwest Atlantic

Anomalous SST gradients were much stronger in this early period.

16 The SST Response to Warm Episodes in the Northwest Atlantic Warm phases in the Northwest Atlantic in the period were tied to a colder globe. Anomalous SST gradients were much stronger in this early period. Warm phases in the Northwest Atlantic in recent decades are tied to a warmer globe. Anomalous SST gradients are reduced due to weaker cold pools. The Response to Warm Episodes in the Northwest Atlantic

The 2000-2018 700mb Response to Warm Episodes in the Northwest Atlantic High pressure ridges are shifted to towards the west

Ridge Separation 120 longitude The 1950-1997 SST 700mb Response to Warm Episodes in the Northwest Atlantic High pressure

17 The mb Response to Warm Episodes in the Northwest Atlantic High pressure ridges are shifted to towards the west coasts of North America and Europe. The flow is rather zonal with weak troughs. Ridge Separation 120 longitude The SST 700mb Response to Warm Episodes in the Northwest Atlantic High pressure ridges are shifted to the east compared to the recent decades. The flow is meridional with troughs western North America and western Europe. Ridge Separation 120 longitude

18 Northwest Atlantic Warm Pool Influences on Precipitation Change in Surface Temperature (left) and Precipitation Rate (right) The impacts on air temperature favor warmer weather in North America. This recent period has had a more active ITCZ south of Mexico that extends into central Mexico but the period has been drier farther north in west central Mexico.

19 X GULF OF ALASKA SSTS Current SSTs in the Gulf of Alaska are at historical highs. This is common with El Nino events. QUESTION: How do SSTs in the Gulf of Alaska impact world SSTs and 700mb heights in the winter? NOV. SSTs

20 Warm and Cold Phases in the Gulf of Alaska December-February 700mb Height Responses to Alaska SSTs December-February W A R M C O L D

Warmer waters in the Gulf of Alaska favor a southward displaced jet stream and these years have a stronger feed of moisture from

21 Gulf of Alaska SST Influences on Precipitation Change in Surface Temperature (left) and Precipitation Rate (right) Differences Between Warm Years and Cold Years Since 1974 Warm Gulf of Alaska winters have been warmer along the west coast of the U.S. and Mexico compared to Cold Gulf of Alaska winters. Warmer waters in the Gulf of Alaska favor a southward displaced jet stream and these years have a stronger feed of moisture from the ITCZ towards an active subtropical jet stream across Mexico and the southeastern U.S.

Currents. History. Pressure Cells 3/13/17. El Nino Southern Oscillation ENSO. Teleconnections and Oscillations. Neutral Conditions

Currents. History. Pressure Cells 3/13/17. El Nino Southern Oscillation ENSO. Teleconnections and Oscillations. Neutral Conditions Teleconnections and Oscillations Teleconnection climate anomalies being related to each other over a large scale Oscillations: Macroscale movement of atmospheric systems that can influence weather, climate,