| RAMMB CIRA 4th Quarter Report |
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July August September 2008 |
Tropical Cyclone Current Product Development
The Tropical Cyclone Formation Probability (TCFP) product has been running in pre-operational mode since July 2008. Promotion to operational status has been delayed due to a freeze instated on all sateps machines in July. The TCFP product has run smoothly in pre-operational mode since July and is currently being quality controlled and monitored by the ESPC help desk. All documentation has been finalized and turned in. Promotion to operational status should occur very shortly after the system freeze is lifted, which is estimated to occur at the end of September. (A. Schumacher, M. DeMaria, J. Knaff)
Figure 1: The TCFP product for the Western N. Pacific domain prior to (left) and after (right) the formation of WP192008 Typhoon Jangmi.
In an effort to improve the tropical cyclone formation probability guidance product, large-scale vertical motion will be added as an additional screening parameter, and its affect on the skill of the forecast measured. The large scale vertical motion field will come from a Q-vector form of the omega equation valid over the entire sphere, which will use the GFS model fields as input. The computation of the Q-vectors has been completed. The next step will be to solve the omega equation over the entire sphere using a vertical normal mode and a spherical harmonic transform. (J. Dostalek)
Progress continues on the operational transition and continued development of the Mult-platfom Tropical Cyclone Surface Wind Analysis (MTC-SWA). This quarter most of the progress has been in two key areas 1) preparation for transition to operations and 2) expansion of uses and customer base. To prepare for the operational transition of the product to the National Satellite Operations Facility (NSOF) a Critical Design Review (CDR) was presented and a sizing requirement submitted. These steps are designed to improve planning encouraging interactions between all parties involved. Several potential logistic problems were solved by the CDR.
Another preparation for operational transition to NSOF was the local development of a dedicated MTC-SWA web page. The currently experimental product creates satellite based surface wind analyses for global tropical cyclones, including areas under investigation according to the Tropical Prediction Center, Central Pacific Hurricane Center, and the Joint Typhoon Warning Center. Archival of this product continues on the RAMMB TC web page/database. The web page can be found at http://rammb.cira.colostate.edu/products/mtc_swa/.
In the last quarter we have also been trying to build the potential customer base for this project. In this endeavor we have made these resulting surface wind analyses available as a text file. One private company, World Winds Inc. has been using our wind fields as a nudging influence to their nowcasting tools. Those tools provide off-shore wind information to XM satellite subscribers. Another potential use is to provide simple information as to how to rotate the microwave input to the Ensemble Tropical Rainfall Potential (TRaP) product that is undergoing development. Our solution was to calculate the vortex Rossby wave propogation speeds (n=2,k=2) given the azimuthal mean wind field. An example is shown below (Figure 2) for Hurricane Gustav 1 September at 06 UTC. (J. Knaff)
Figure 2: Radial profile of azimuthally averaged radial (Ur) and tangential (Vt) winds from the MTC-SWA and the radial (U_band) and tangential (V_band) propogation speeds of vortex Rossby waves with radial and azimuthal wavenumbers equal to 2.
A new AMSU-based real-time experimental tropical cyclone product is being created. The product makes use of the wind fields derived as part of the CIRA/RAMMB AMSU tropical cyclone intensity and structure algorithm run at NCEP (i.e., by solving the non-linear balance equation). Using these wind fields that are created on standard pressure levels for every tropical cyclone viewing opportunity, two estimates of the vertical wind shear and two estimates of mass-weighted deep-layer mean steering flow are created. Often the latest estimates of these quantities are available before the GFS analyses become available in operations, and therefore may be useful for nowcasting subtle changes in the TC environment. An annotated example of the product is shown below (Figure 3) for Hurricane Bertha (2008). In that figure notice: 1) that the maximum intensity corresponds to the storm dramatically slowing down in an already low vertical shear environment, 2) the deep and shallow layer mean steering captures the near stationary nature of the storm on the 12-13 July, 3) at the point of recurvature the steering directions are nearly exactly 180 degrees, and 4) other intensity maxima associated with this long-lived tropical cyclone occurred during periods when the vertical shear is decreasing. Plots like the one below will be generated in a real-time manner and then displayed and archived on the RAMMB tropical cyclone web page (http://rammb.cira.colostate.edu/products/tc_realtime/index.asp). For further information on these vertical shear estimates, see Zehr et al. (2008); http://ams.confex.com/ams/pdfpapers/137917.pdf. (J. Knaff, R. Zehr, K. Micke)
Figure 3: AMSU-based estimates of vertical wind shear and mean steering flow for Hurricane Bertha that has been annotated to show key events in Bertha’s history. Shown are 200-850 hPa vertical wind shear speed and direction (top panel), 500-850 hPa vertical wind shear speed and direction (second panel), 200-850 hPa mass-weighted mean wind speed and direction (third panel), 500-850 hPa mass-weighted mean wind speed and direction (bottom panel), All calculations are based on averages of AMSU-based wind fields within 600 km of the tropical cyclone center.
New NOAA-16 AMSU temperature retrieval coefficients were provided by M. Goldberg, C. Barnet, and Z. Chen (SMCD) to account for the intermittent failure of channel 4, which began in March. The coefficients allow for temperature retrievals over tropical cyclones and provide the basis for tropical cyclone intensity and structure estimates. Currently the NOAA-16 –based tropical cyclone intensity and structure estimates have been adversely impacted by the channel 4 failure, resulting in a dramatic decrease in the number of TC fixes from NOAA-16 as well as a noticeable decrease in accuracy of the fixes that do occur. The new coefficients have been tested both at CIRA and TPC. The new coefficients also required small changes in the operational code run at NCEP. The new coefficients and software were provided to NCEP Central Operations for implementation on the NCEP supercomputer and were implemented on 16 September following Hurricane Ike. This has already resulted in a noticeable increase in the number of fixes. (J. Knaff)