Part C: Heat Energy for Katrina

The rapid intensification of tropical cyclones is an important area of current research. Rapid intensification is defined as wind speeds that increase by 30 knots or more in less than 24 hours. Scientists are actively investigating how the amount of heat energy available in the upper ocean affects the intensity of storms. They want to use this information to improve predictions about how intense a storm will be when it makes landfall.

Heat content of the ocean is important because the warmer the ocean water is, the more easily it evaporates into water vapor. Water vapor takes heat energy from the ocean into the atmosphere. When the water vapor re-condenses into liquid water, it releases the heat energy and makes it available as power for further wind and rain. In the right atmospheric conditions, heat energy contained in the ocean can be considered as fuel for hurricanes.

2005's devastating Hurricane Katrina is one example of a storm that experienced rapid intensification. Hurricane Katrina encountered the Gulf Loop Current in the Gulf of Mexico and intensified overnight from a Category 3 to a Category 5 hurricane. Did Hurricane Katrina take stored heat energy from the ocean? In this Part of the lab, you'll use data from the NOAA View Data Exploration Tool again to examine several data products (images) that depict the amount of heat energy available in the Gulf of Mexico just before Hurricane Katrina moved through it. You'll download some of these data to use in Google Earth with the pathway of Katrina you mapped in Lab 4A. You'll also examine data to check whether Hurricane Katrina was able to use heat energy for power.

Stop and Think

2. Read the summary above. Use your own words to describe how heat in the ocean provides power for tropical storms.

Add Data toolbar

  1. Visit the NOAA View Data Exploration Tool again. This time the link will take you to the overview page. You'll be gathering three data sets, to export for use in Google Earth for analysis.
  2. On the left, click Add Data > Ocean > Temperature > At the Surface
  3. The map of the oceans will now show temperature data for the most recent data set. Click the button to view Weekly Data. Use the slider at the bottom of the left panel to scroll through different dates.
  4. Next, you'll retrieve data from the weeks of Katrina. Click the Download button on the left panel. Select Google Earth, and "Over a date range" and select 2005 for both years and From "08/22 to 08/28" and To "8/29 to 09/04". Then select Download. You may want to save the kmz file by adding "Katrina" to the beginning of the file name so your files will be easier to find or by having a folder on your desktop to save everything into.  
  5. Once you've downloaded Sea Surface Temperature Data, you're going to go back to the Add Data button on the left panel and use the Back button to return to the top level.  
  6. Repeat these steps to retrieve the same data for Sea Height Anomaly, and Tropical Cyclone Heat potential. Be sure to get the same dates for each set of data. Note: If the dates don't align exactly, make sure there is overlap with the dates of the storm.

  7. Once you've downloaded the three kmz files of NOAA data, open Google Earth. Open the kmz file containing the track you plotted from Lab 4A of Katrina's HURDAT data points. Make sure the layer is turned on.
    NOAA Data layers
  8. Open the three kmz files you downloaded of NOAA data in Google Earth. The three layers will overlap, so turn off two data layers so you can read one at a time and the corresponding data color key.
  9. Compare each data image to the track of Katrina. Use the slider at the top left to move between data images and see how the ocean data changed during the storm. When your mouse hovers over the time slider, the the Time Options tool will appear in the upper right of the box.
    Click to open the dialog box, and change the time display to UTC, this will match the time entries in HURDAT. The time coordinates of your data path will now match the time coordinates of the NOAA data, and you can better consider the mapped data.  

Interpreting the Data Images

Each data image shows land in gray. Various colors over the waters of the Gulf of Mexico indicate heat content of the water. Examine the color scale to the right of each image to interpret what the colors mean.

Sea Surface Temperature

Satellite-based sensors record the amount of radiation emitted in different wavelengths over our whole planet every day. Scientists apply mathematical algorithms to these data to produce images that show the temperature of water surfaces. The indicated temperatures are regularly checked against measurements recorded by ships and buoys.

Sea Height Anomaly or Sea Surface Height Departure

As the temperature of water increases, it experiences an increase in volume. At the molecular level, the faster motion associated with higher temperatures means that individual molecules push each other further apart, resulting in a larger volume. Though this increase in volume can't be seen in small amounts of water, warm areas of the ocean exhibit a "swelling" that can be detected by satellite instruments. Similarly, colder water decreases in volume and may result in an area that is lower than average sea level. Altimetry sensors on satellites collect data that show areas where sea level is higher or lower than average. Areas where the ocean surface is above or below mean sea level show up as sea height anomalies in these images; areas that are higher than average represent areas of warm water, areas with lower than average sea levels indicate cold water.

Tropical Cyclone Heat Potential

The Tropical Cyclone Heat Potential (TCHP) is an estimate of the amount of heat energy that is available to power tropical cyclones. The Atlantic Oceanographic and Meteorological Laboratory (AOML) has defined TCHP as the integrated vertical temperature from the sea surface to the depth of the 26°C isotherm. The 26°C isotherm (iso = same; therm = temperature) is at some depth below the surface for all areas where the surface temperature is 26°C or above. The deeper the depth to this isotherm, the higher the heat energy that is available to transfer to the surface. This essentially means that higher sea surface temperatures and deeper depths of the 26°C isotherm indicate that more heat energy is available to power storms.

Analyzing the images

  1. As Hurricane Katrina moved over the Gulf of Mexico, did it take the stored heat energy from the ocean? Compare the downloaded information of TCHP against the storm track to check if there was heat potential to be utilized by the storm.
  2. Use the Ruler tool from the Google Earth toolbar, then click over the starting point and again at the end point across any ocean feature in the different data layers image. The popup ruler box will read out the measurement. Make sure to change the units to kilometers

Stop and Think

3. On the Sea Height Anomaly image, what are the dimensions (length and width) of the area that is over 25 cm above mean sea level during the time Katrina passed over that part of the ocean?

4. Describe any patterns you see between the storm's track or its intensity and what's happening in the ocean water it's passing through.

5. Looking at Katrina's path, describe how the Tropical Cyclone Heat Potential data supports the idea that heat energy in the upper ocean is available to power tropical storms.

What's the Tropical Cyclone Heat Potential for Today?

You can access the same types of heat energy images you just explored for other locations and dates. You may want to examine data for other storms that have occurred since January 1, 2005, or just check current conditions.

  1. Visit the NOAA View Data Exploration Tool again.
  2. Focus the map into the Gulf of Mexico, and find the dataset for TCHP. Scroll through the date bar on the left panel to see how the most recent images compare with August of 2005.
  3. Look at the current Global TCHP image to see what locations have the highest TCHP.

Checking In

  • Where on Earth is the Tropical Cyclone Heat Potential highest today?
  • Describe today's conditions in the Gulf of Mexico with respect to heat energy.

Stop and Think

6. Skim through his NASA news article to see how the information you've explored in this lab was presented to the public. Write a brief summary to describe why this heat energy research is important to people.