Lab 12: Hurricane Sandy, Claire Mundi

For this blog post I will be revisiting my case study from the first lab: Hurricane Sandy. Hurricane Sandy made landfall over the eastern US on October 29, 2012.

Corrected Reflectances

Figure 1. Corrected reflectance loop of Hurricane Sandy making landfall over the east coast (Terra/MODIS). Loop is daily images from October 25 – 31, 2012.

In the corrected reflectances, a significant cyclone structure is evident. Figure 1 shows the white clouds approaching the eastern coast of the United States. While these RGB true-color images are useful for identifying the presence of a storm, they otherwise do not provide much additional information or insight to the storm characteristics or evolution.

 

Precipitation

Figure 2. Precipitation rate from October 27, 2019 (two days before landfall). This date was selected such that the entire storm falls beneath the approximate 40° latitude cutoff of TRMM. Color scale shown below.

The addition of this layer provides more information about storm intensity. The precipitation rates range up to just over 25 mm/hr. Overall, the storm is strongest near its center and weakens outward. As shown below, the regions with the most intense precipitation also correspond to the regions of highest cloud top heights.

Clouds

Information about the cloud properties can be obtained from satellite data products derived from other wavelength observations. For example, the following set of figures show the cloud effective radius and cloud top height.

Cloud effective radius 

Here it is evident the clouds composing the cyclone are a mix of liquid and ice phase drops. Looking at the cloud effective radius (Figure 2), the clouds are made up of a wide range of drop sizes, with ice particles ranging from 5 to 60 μm and water drops ranging from 4 to 30 μm. Overall, the cyclone appears to be dominated by larger ice particles (between about 40 and 60 μm). Near the eye of the hurricane and outer edge (to the southeast) the water drops are at their largest. Referring back to the precipitation plot above, the regions with the largest effective radii respond to regions of the highest precipitation.

 

Figure 2. Cloud effective radius layer from October 29, 2012, the date of landfall (Suomi NPP/VIIRS). Color scale shown below.

Cloud Top Height

Figure 3. Cloud top height variable from October 29, 2012 (Suomi NPP/VIIRS). Color scale shown below.

 

The cloud top height variable (Figure 3) provides a relatively good match to the radar derived heights found in my first lab (shown in Figures 4 and 5). From the NEXRAD radar data (Figure 5), the observed reflectivity across the transect range from about 4 km up to about 15 km. Likewise, the satellite data in WorldView shows cloud top heights along the same approximate cross-section from about 4 km (in green) to heights exceeding 12 km (shown in the light pink). 

Figure 4. Radar reflectivity from about 12 pm ET on October 29 with the red transect showing where the cross-section shown in Figure 5 was taken.

Figure 5. Cross section of reflectivity values along the transect in Figure 4. As the distance along the transect increases, the latitude increases northward. Colors match the scale shown in Figure 4.

One major difference between these two data sources in the resolution. In the NEXRAD plot, we see the vertical bins extend a few kilometers, especially further from the location of the radar. The WorldView image provides a much more continuous display of data. Therefore, for the radar data, it is difficult to determine the maximum cloud top height within the uncertainty of the radar bin. Additionally, the NEXRAD radar may not be able to resolve smaller cloud droplets as a satellite instrument with a higher frequency would be able to. Being able to detect smaller droplets would alter where the cloud top height is defined.

Geostationary Layers

Unfortunately, this event happened several years ago, so geostationary layers are not available for this case. However, it would be interesting to see if there is any evidence of convection from the Red Visible and Clean Infrared geostationary layers. With these layers, we may have been able to see “lumpy” cloud tops in the visible layer or enhanced-V structures in the infrared.