This week, we're going to work through an online exercise using the NCAR/NCEP Reanalysis dataset.
A 'reanalysis' blends together climate data observations from many different sources - land stations, ships, weather balloons, aircraft, and satellite - and runs it all through a weather simulation model. The end result is a decades-long estimate of different aspects of the Earth's climate system, and that data is very useful for understanding how the climate system varies today and how it affects aspects of the land surface.
We will spend 2 classes working through the reanalysis toolset and creating several data visualizations related to important aspects of climate. Because 'the present is the key to the past, you may also decide to use this tool when describing the paleoclimate of your study region.
Please include your plots and maps in the response you submit to me on March 5 (beginning of class).
COMPOSITES AND ANOMALIES
Question 1. Visit the page on 'Monthly/Seasonal Climate Composites' at http://www.esrl.noaa.gov/psd/cgi-bin/data/composites/printpage.pl. First, create a single map showing sea-surface temperature anomalies (use the variable 'NOAA Extended SST') for the period December to February for the following years: 1957-58, 1969-70, 1972-73,1982-83, 1993-94, 1994-95, 1997-98, 2002-03 and 2009-2010. Describe the spatial patterns present in the anomaly map (and their magnitudes in degrees). Please be specific when describing those regions where sea-surface temperatures are unusually high or low. What aspect of the climate system is most obvious in your map?
Second, create another single anomaly map for the same set of years, this time plotting the Palmer Drought Severity Index (PDSI). The PDSI, which estimates local drought conditions using a simple model of soil moisture, maps both unusually wet (large positive numbers) and unusually dry (large negative numbers) conditions. What is the spatial pattern of drought that is associated with those anomalous sea-surface temperatures shown in your previous map?
Finally, repeat the first and second parts of this question using a different set of years (1955-56, 1970-71, 1973-74, 1975-76, 1984-85, 1988-89, 1998-99, 1999-2000 and 2010-2011) and answer the same questions about SST and drought patterns.
Question 2. One alternative to mapping climate variables is to create plots that average conditions across lines of either latitude or longitude. Plot mean zonal winds for January and July 2011 by latitude, showing both the Northern and Southern Hemispheres. What is the main component of the climate system that is visible in these maps? And why does it change between the two seasons, particularly in the Northern Hemisphere?
CORRELATION AND REGRESSION
Question 3. Visit the page 'Linear Correlations in Atmospheric Seasonal/Monthly Averages' at http://www.esrl.noaa.gov/psd/data/correlation/. Correlate the time series for the North Atlantic Oscillation (NAO) with sea level pressure during winter (December to February).
First, please define the North Atlantic Oscillation. Second, plot the result using a map showing only the Northern Hemisphere (Plot Region/Type 'Northern Hemisphere'). Include the map in your response and describe its the major features. Third, repeat the analysis using regression instead of correlation. How has your map changed? Hint - look closely at the units associated with each map.
Question 4. Regress the variable called 'Nino 3.4; against winter air temperature at the surface. Your map should illustrate the regression pattern across all of North America; don't show only the United States.
First, explain what the 'Nino 3.4 index' physically represents (you will need to find this description yourself). Second, describe the pattern and magnitude of response exhibited by North American temperatures to the El Nino-Southern Oscillation. Make sure to describe the association between regional temperatures and both aspects of ENSO ('warm' El Nino events and 'cold' La Nina events).
PLOT TIME SERIES
Question 6. Visit the page 'Create a monthly/seasonal mean time series from the NCEP Reanalysis Dataset' at http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl. Plot the time series for average annual (January to December) air temperature for the region around the Twin Cities (roughly 45°N 93°W). What are the warmest and coldest years in this record? How have temperatures in the region changed during the period of record?