Investigating El Nino's Impact on Washington, D.C.

Introduction

An El Nino occurs as a result of the atmosphere and the ocean interacting together. El Ninos happen mostly in the equatorial area of the Pacific Ocean. The motion of the atmosphere over the ocean depends on the sea surface temperatures (SSTs) and where it is warm and cool. The SST is partly determined by the atmospheric circulation happening above it. Scientists use the the phrase "coupled interaction" to describe this relationship between the ocean and atmospheric circulation. When SSTs in the central and eastern Pacific are warmer than usual it is called an "El Nino" and when they are colder than normal, it is called a "La Nina". The cycle between cold and warm ocean temperatures takes three to five years.

Upper-level flow features over the North Pacific and North America during December 1994 & January 1995. (NOAA, 1998)

El Nino (and La Nina) are important for us in the United States because the atmospheric circulation changes they cause are felt in various ways around the world. Over the last 65 years, about twelve El Nino's and La Nina's have been observed. The diagram below shows strong and very strong El Nino years since the mid 1500's. In addition 1991/92, 1994/95, and 1997/98 have been El Nino years. (NOAA) In this report we will study whether we can see evidence of the impact of El Ninos on the temperature in the Washington, D.C. metropolitan area.

Our research question is this:

Is the Washington, D.C. metropolition area's weather affected by the El Nino changes? We will look for evidence of changes in the average monthly temperatures in the D.C. area during the winter months of January, February and March. First we will compare the predictions of El Nino's influence published by the National Weather Service during last Fall, 1997 with data on average temperatures during the winter months of this year, 1998. We will also examine historical data for the winter months back as far as we can find it, and compare with past El Nino years to see if there is any evidence of El Nino's impact. We limited our research to average temperatures due to our limited amount of time. We're also curious about precipitation data.

Hypothesis

We believe yes, El Nino has affected the Washington, D.C. weather this winter, because we feel the changes already compared to last year's weather - El Nino affects Washington. D.C.'s weather by making the temperature rise unusually. The news has been full of reports that our warm winter was caused by El Nino's influence.

We read the National Oceanic and Atmospheric Administration"s (NOAA) predictions for El Nino's influence on the winter of 1998. NOAA said that North America receives its strongest El Nino impact during the winter and early spring. They predicted warmer and milder than normal conditions across the northern tier of the USA and cooler and wetter than normal conditions across the Gulf Coast for this winter. Washington, D.C. is pretty much in the middle of the country and their "Outlook" maps do not show much impact predicted for our area.

Procedure

The process used in finding the specific data for our research question was to analyze the present (1995-1998) data from the national weather service, and G.L.O.B.E. (Global Learning and Observations to Benefit the Environment), which is a network of students and faculty collecting weather information from their area from points around the globe.

From the National Weather Service, we found interesting data which indicates El Nino's effects. We also used a World Weather Data CD-Rom to find average monthly temperatures for January, February, and March back to 1820. We made a graph of the data, then used a graphics program called Paint Shop to add 1993-1998 averages to each month. Then we added lines to show the El Nino years (in red).

We analyzed the 1998 averages and we analyzed the graphs. Then we wrote up our report.

Data

GLOBE Student Data Visualization

[ credit ]

Chart summarizing the monthly averages:

Year	Month	Average Temp (deg C)	30-year Norm (deg C)	Deg above/below Norm
1998	March	8.76	8.28	+.50
	February	6.51	3.11	+3.40
	January	6.11	1.39	+4.72
1997	December	5.0	4.11	+.89
	March	9.20	8.28	+.92
	February	6.62	3.11	+3.51
	January	2.70	1.39	+1.31
1996	December	6.11	1.39	+7.5
	March	6.06	8.28	-2.22
	February	2.89	3.11	-0.22
	January	0.44	1.39	-.95
1995	December	1.89	4.11	-2.22
	March	7.72	8.28	-0.56
	February	-0.28	3.11	-3.39
	January	2.61	1.39	+1.22
1994	March	5.22	8.28	-3.06
	February	0.44	3.11	-2.67
	January	-3.39	1.39	-4.78
1993	March	1.85	8.28	-6.43
	February	-.5	3.11	-3.61
	January	.15	1.39	-1.24

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Graphs showing monthly averages since 1820. El Nino years are shown with red lines.

[ World Weather Data CD ROM ]

Results

We studied data for December, January, February and March for 1993-1998. First we compared our school's GLOBE data with normal averages for each month. The first graph shows how the current air temperature and the maximum air temperature usually show up above the average temperature. In one place in early January all three (current, Minimum, and Maximum) temperatures are much above the average.

During the time we studied (1993-1998) Washington, D.C. had the warmest 4 winter months in a row for this year, 1997/98 (+.89, +4.72, +3.40, and +.50 degres C above the 30-yr normal). This supports the prediction that the El Nino this year had a warming effect on Washington, D.C's winter weather.

After analyzing the historical data presented, I have concluded that while El Ninos do occur with temperatures that are lower than usual, there are few other low temperatures that do not parallel with El Nino occurings. The graph suggests that when El Nino occurred in the past, it decreased the temperature by a few degrees in the Washington, D.C. area. But for 1997/98 El Nino seemed to increase the temperatures. When we analyzed extreme weather records for Washington, D.C. only a tiny number of extreme records occurred during El Nino years, so it does not seem like El Ninos cause extreme temperatures in our area.

What the Scientists have to say

NOAA Precipitaion Summary and Temperature observations

Conclusion

After having analyzed the data above and a sundry of other such, I have concluded that there is definitely a pattern in temperature changes in the Washington, D.C. area for the 1997/98 winter. The four months I studied were above the 30-year normals for temperature. I also wondered about past El Ninos. Looking at the graphs it looks like average temperature increased in the winter by +1.6 deg. Celsius, and decreases in the summer by -1.4 degrees Celsius; while in other normal years, there were no such drastic changes as previsously mentioned. After comparing the recent El Nino years, it is interesting to see the changes increasing with each El Nino passing.

Through a study done by Thomas P. Guilderson and his colleagues of Howard University, corals of the Pacific ocean show signs of El Nino changes decades ago. After the nuclear tests of the early fifties, radiocarbons travelled through winds, and landed on certain parts of the ocean itself, and were absorbed by the corals below, where they stayed for decades. In the present year of 1998, meterologists discovered the radiocarbons and the connection between those radiocarbons and El Nino occurings. The connection was, they believe, back in the year of 1976 where a "huge" El Nino change had occurred -- they noticed that the radiocarbon level on the corals rose, and along with it carbon-14 which is how the scientists measure time, through decaying carbon-14. That means there was a huge upwelling in that year, as well as increases in the changes in the following El Nino years. My conclusion is this; El Nino's effects increase with each El Nino year. I am sure others are asking the same question I am asking: why?