Hurricane Rina, Irene, and the Multi-Platform Tropical Cyclone Surface Wind Analysis

Hurricane Rina provides an opportunity to examine the Multi-Platform Tropical Cyclone Surface Wind Analysis (MPTCSWA) from CIRA. This product is intended to provide “estimates” of the 1-minute maximum winds at 10-m elevation. Note that there are lots of limitations with this data set and approach but the summary of the approach provides some interesting points including a land reduction factor. The notes below described the MPTCSWA data and were copied from this link on the RAMMB / CIRA web site.

Currently, the MPTCSWA combines information from five data sources to create a mid-level (near 700 hPa) wind analysis using a variational approach described in Knaff and DeMaria (2006). The resulting mid-level winds are then adjusted to the surface applying a very simple single column approach. Over the ocean an adjustment factor is applied, which is a function of radius from the center ranging from 0.9 to 0.7, and the winds are turned 20 degrees toward low pressure. Over land, the oceanic winds are reduced by an additional 20% and turned an additional 20 degrees toward low pressure.

The five datasets currently used are the ASCAT scatterometer, which is adjusted upward to 700 hPa in the same manner as the surface winds are adjusted downward, feature track winds in the mid-levels from the operational satellite centers, 2-d flight-level winds estimated from infrared imagery (see Mueller et al 2006 ) and 2-d winds created from Advanced Microwave Sounding Unit (AMSU)- derived height fields and solving the non-linear balance equations as described in Bessho et al (2006). Past analyses also made use of the QuickSCAT scatterometer (i.e., prior to November 2009), but this satellite is no longer producing observations of surface vector winds.

Some verification from the 2007 season suggests that analysis tends to have a high and large aerial bias – verification results.

Archived imagery for Hurricane Irene is available at this link. An example image from Irene as it moved across eastern North Carolina is shown below. This wind analysis is more limited in complexity than others such as the HRD Surface Wind Analysis for Irene, and the MPTCSWA analyzed winds that were too strong over inland locations in central and eastern North Carolina. The wind analysis along the immediate coast was much more similar between the two methods, once again pointing to issues with wind reduction techniques over land, well inland for the beach front.

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2 Responses to Hurricane Rina, Irene, and the Multi-Platform Tropical Cyclone Surface Wind Analysis

  1. bptyner says:

    Thanks for the post, JB. I think this shows once again how assimilating different sets of data can provide different wind verifications. As you point out, this is most noticeable for Irene in areas further inland. I will try and take a look at some other storms to see if this trend holds. Because HWIND analyses do incorporate surface observations, I would think they probably have more accuracy in handling some of these inland locations, where the differences in the two plots is evident. As the plots suggest, land reduction factors clearly need some modification, especially when deriving surface wind speeds for areas far inland from fight-level winds

  2. Pingback: Some Observations and Forecasts of Wind and Wind Gusts Associated with Isaac as it Made its Second Landfall | CIMMSE

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