« Back

What Happens Inside Clouds and Storms? A Case Study of Hurricane Joaquin


Most cloud observations, including those using the GLOBE Observer app and even many from satellites, focus on the surface of clouds. It’s also useful, however, to be able to look inside clouds, especially storm clouds, to be able to get a picture of what’s going on now, and what might happen next.

As an example, let’s look at Hurricane Joaquin, which was over the Caribbean in late September 2015. First, some ground observations from GLOBE overlaid on satellite surface reflectance data (below). On September 29th, the closest data point to the storm (center of image) is from Ramey School in Puerto Rico, which reported scattered cloud cover and cumulus and cirrus clouds (screen capture and observation details from the GLOBE Science Data Visualization tool).

But how can we look inside the clouds? The CloudSat satellite uses a cloud-profiling radar to get a vertical slice through the cloud. Look at the images below, also from September 29th. The top image shows a natural-color view of the storm acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Aqua satellite. The red line is the south-to-north track that CloudSat took over the storm.

The bottom image is that slice of data. Dark blues represent areas where clouds and raindrops reflected the strongest signal back to the satellite radar. These areas had the heaviest precipitation and the largest water droplets. The blue line in the center of the image is the freezing line; ice particles formed above it, raindrops below it. (For more information, see the Earth Observatory article that was the source of these images.)

Now we’re starting to get a betting picture of what’s going on in the storm, but we can actually do even more. In February of 2014, NASA and the Japan Aerospace Exploration Agency launched the Global Precipitation Measurement mission, which has a special Dual-frequency Precipitation Radar aboard. The DPR is able to detect precipitation rates, whether the precipitation is solid or liquid, as well as the sizes of droplets in a cloud, and gives us a three dimensional view of the storm. (You can see a neat animation of both of the GPM instruments here.) GPM also captured an image of Joaquin on September 29th as the hurricane moved slowly towards the west-southwest about 400 miles east of the Bahamas. Listen to GPM Deputy Project Science for Applications, Dr. Dalia Kirschbaum, (briefly) explain in the video clip below:

(For a longer view of the animation, visit NASA Goddard’s Scientific Visualization Studio, also the source of the next few images and some of the text on this page.)

The DPR instrument gives us a wider swath than CloudSat, to see more of the storm. We can pull out some still images from the animation to look at more detail. Notice the areas of very intense rain with rain rates ranging from around 50 to 132 mm/hr (~2 to 5 inches, shown in shades of red) just to the right of the center of the storm in the image below.

This shows that large amounts of heat are being released into the storm's center, fueling its circulation and providing the means for it to intensify. Associated with the area of intense rain is an area of tall convective towers, which when observed near the storm's core are a strong indication that the storm is about to strengthen. You can see them in the image below as the taller blue areas to the left-center of the image.

The instruments from CloudSat and GPM can give us the inside view of clouds and storms, but only when they pass over a particular area, so we will always still need the broader view of the surface of the clouds, from satellites and from observers on the ground.

Comments
Please log-in to post comments