Atmosphere-ocean interactions can impact large-scale atmospheric circulation in one part of the world and affect the weather of another part of the world even 1000s of kilometers apart. These are teleconnections.

The ElNiño Southern Oscillation (ENSO) is one such teleconnection.El Niño and La Niña events are associated with changes in the ocean temperatures in the Pacific Ocean near the equator.The normal situation is a cold current off the coast of Peru, higher atmospheric pressure in the eastern Pacific and lower atmospheric pressure in the western Pacific driving strong trade winds. During an El Niño event, the current waters near Peru are warmer, there is less high pressure, the trade winds are weaker, and a large area of the eastern Pacific warms. During La Niña, the opposite occurs and the eastern Pacific cools.

The Southern Oscillation Index (SOI) is a measure of the large-scale changes in the difference in surface pressure between the western and eastern tropical Pacific.

ENSO and winters in Ottawa

The 2015-16 Rideau Canal Skateway season was the shortest on record. This winter also happened to be during a strong El Niño event. Use the posted data for the past ~ 40 years to investigate any potential relationships between ENSO and Ottawa winter conditions and the Skateway season.

Laboratory Assignment Questions:

Note: All questions must be answered with complete sentences.

All questions requiring calculations must include sample calculations, which will include the original formula used and units included throughout.

Ensure there is a space between the number and the unit and between parts of units. For example, m s-1. Always check that the units work out.

The Lab Appendices posted on CULearn include instructions on the use of significant figures. We are concerned primarily that a reasonable number of digits are used appropriate for the resolution of the measurement.

Also see the Lab Appendices for the required presentation format for tables and figures in this course.

Make sure to cite your sources of information. We suggest including a statement up front such as "The following statements refer to information found in Ross (2013) unless otherwise stated." Be sure to include references at the end of your submission.

1. Whydo El Niño and La Niña events impact the path of the wintertime jet streams over North America? Include in your answer a description of how the jet stream paths differ and the resulting general differences in weather with respect to central Canada and into Ontario (when appropriate). To help you with this answer, refer to Figure 1 and the following websites: http://www.srh.noaa.gov/jetstream/tropics/enso_impacts.htm

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensocycle/nawinter.shtml.

2. In your dataset, La Niña years have been numbered 0 (normal), 1 (weak La Nina), 2 (moderate La Niña), and 3 (strong La Niña). Similarly, El Niño years have been numbered 0 through 4 with 4 as very strong El Niño.

a) Plot La Niña year categories vs. SOI averaged for December through February (DJF). Label as Figure 1 with a descriptive caption.

b) Plot El Niño year categories vs. SOIaveraged for DJF. Label as Figure 2 with a descriptive caption.

c) How does SOI relate to ENSO events?

3. a) Plot the Skateway season opening date over time (year). Note that the dates are given as day of year (Jan 1 = 1) with dates in December as negative values (Dec 10 = -21). Label as Figure 3 with a descriptive caption.

b)Plot (but do not include in this report) the Skateway season length vs. opening date and vs closing date. Does the season length depend more on opening date or closing date?

c) Plot the Skateway season length vs. the mean DJF air temperature. Label as Figure 4 with a descriptive caption. Does there seem to be a relationship there? Describe it.

4. a) Plot the minimum and mean DJF air temperature in Ottawa vs. the DJF SOI. In your report, include the plot of the minimum DJF air temperature. Label this as Figure 5 with a descriptive caption. Does there seem to be a clear relationship?

b) Plot the Skateway season opening date vs. the DJF SOI. Label as Figure 6 with a descriptive caption.

c) Plot the length of the Skateway season vs. El Niño strength category. Label as Figure 7 with a descriptive caption.

d) Is there a clear indication of ENSO impacts on the Skateway season?Why do you think ENSO does or does not relate to the Skateway season statistics?

References

Ross, S.L. 2013. Weather and Climate: an introduction. Oxford University Press. 510 pp.