U of M GEOG 5426 - INTRODUCTION TO THE NCEP - NCAR REANALYSIS

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GEOG5426 CLIMATE VARIATIONSEXERCISE 1: INTRODUCTION TO THE NCEP/NCAR REANALYSISComposites and anomaliesQuestion 1. Geopotential height is one of the primary variables used to describe the state and structure of the atmosphere. In a short paragraph, provide the definition for geopotential height and explain briefly how it can be useful in climatological analysis.Question 2. I’ve created three maps that illustrate the different perspectives that we use to examine the behavior of a climatological field like geopotential height. The first map (a, above left) shows mean geopotential height across North America during winter (December to February), calculated over the period 1949 to 2011. The second map (b, upper right) plots the same variable during a single year (2011) and the third (c, below right) shows the anomaly for that month. In a short paragraph, describe the main features shown on these maps and explain how each of these views (long-term mean, single-year average or single-year anomaly) help us understand the structure of the atmosphere.Question 3. Visit the page on ‘Monthly/Seasonal Climate Composites’ at http://www.esrl.noaa.gov/psd/cgi-bin/data/composites/printpage.pl. First, create a map showing sea-surface temperature anomalies (use the variable ‘NOAA OI SST’) for the period December to February for the following years: 1982-83, 1993-94, 1994-95 and 1997-98. Describe the spatial patterns present in the anomaly map (and their magnitudes). What feature of the climate system is most prominent in your map? Second, create another 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 anomalous sea-surface temperatures? Finally, repeat the first and second parts of this question using a different set of years (1988-89, 1998-99) and answer the same questions.Question 4. 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 regressionQuestion 5. 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 plot the result using a map showing the entire Earth (Plot Region/Type ‘ALL’) and then repeat for only the Northern Hemisphere (Plot Region/Type ‘Northern Hemisphere’). Describe the major features of the second map. Repeat the analysis using regression instead of correlation. How has your map changed? Why do you think regression produces a somewhat different set of spatial patterns?Question 6. Regress Nino 3.4 against winter surface temperature. 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. Next, describe the pattern and magnitude of response exhibited by North American temperatures to the El Nino-Southern Oscillation. Question 7. Describe briefly the difference between correlation and regression. Explain why you might use one tool over the other when comparing a time series to a climatological field.Plot time seriesQuestion 8. 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. What are the warmest and coldest years in this record?Due at the beginning of class on March


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