American Meteorological Society Demo

a morphed microwave product onto geostationary infrared imagery. Animation of this combination creates a simultaneous view of precipitation and cloud distribution, and is similar to an overlay of radar onto geostationary imagery. The microwave imagery used in MIMIC-IR is the polarization-corrected temperature (PCT), which is slightly different from the brightness temperature used in MIMIC-TC. The PCT is computed from a weighted difference between the vertical and horizontal polarizations of the 85–92-GHz frequency, which isolates the signal of precipitation from the surface background (Spencer et al. 1989). (In the MIMIC-TC product, the horizontal polarization brightness temperature is preferred over the PCT because the horizontal polarization shows important textures that indicate the storm’s circulation.) The morphing algorithm itself is exactly the same as that of MIMIC-TC described above. The infrared imagery for MIMIC-IR is taken from the nearest of four possible geostationary satellites TABLE 2. Geostationary satellites used in MIMIC-IR. scheme does not account for this divergent radial motion. In this case the end user must mentally picture the PCT-resolved convection moving in tandem with the infrared-resolved cloud advection. Using this guideline, the visualization of developing cyclones (before a center of rotation is established) can be substantially improved compared to the MIMIC-TC depiction. An example of MIMIC-IR for an earlier sequence of Hurricane Wilma (2005) illustrates the main features of this product (Fig. 6). Here the IR imagery clearly shows that the bands farther than about 2.5° (275 km) from the storm center are moving away from the storm. However, inside this radius the convective activity is obscured in the IR by the cirrus cloud cap, and here the PCT reveals the structure of the inner bands, the eyewall, and a secondary eyewall after about 1200 UTC 21 October. In fact, the PCT reveals that the eyewall is consistently ~50 km in diameter for almost 2 days, while the clouds obscure this fact in the IR for most of this time. CONCLUDING REMARKS. This article introduces a new viSatellite Nadir longitude Basin sualization tool that makes use of morphing techniques to create GOES-East 75°W North Atlantic time-continuous animations of irGOES-West 135°W West Pacific, central Pacific regular satellite images. Specifically, MTSAT 140°E East Pacific, central Pacific the MIMIC-TC tool inputs passive Indoex 63°E Indian Ocean microwave imagery from multiple LEO satellite overpasses of a target (Table 2). The temporal frequency of these satellites’ tropical cyclone and displays a smoothly transitioned images is normally between 15 and 60 min, although movie of the key structure trends. The MIMIC-TC each experiences an occasional data blackout display is especially efficient at visualizing the evo(either because of an eclipse period or because of lution of banding structures, secondary eyewall technical issues), which causes longer gaps in the formation, and eyewall replacement cycles, all of data availability. The infrared image shown in the which are important to the organization and intensity MIMIC-IR product is the one closest in time to the analysis. A derivative of this tool, MIMIC-IR, overlays display time (either before or after). In contrast to the the microwave signatures onto clouds as depicted morphed microwave product, the infrared imagery is in coincident geostationary satellite IR imagery, always displayed in its original position at the image yielding a multispectral visualization of tropical time stamp and is not “nudged” with time to follow cyclone behavior. the TC track. This allows the observer to use the Many areas still require improvement in order to infrared image as a reliable validation for the position more fully optimize the MIMIC algorithms. First, the of matching TC features, as long as the infrared image depiction of features “fading” from one position to is updated rapidly (<30-min intervals). the next (rather than moving continuously) as well as In MIMIC-IR, PCT and infrared are two unique “pulsing” artifacts should be reduced by introducing “layers” of imagery. The PCT layer is semitransparent more realistic motion. Second, the advection functo permit a direct comparison with the underlying tion should be parameterized to match the state (i.e., infrared image. For example, often an outer spiral current size and intensity) of the tropical cyclone. band will move rapidly away from the storm center, This would require regular input information from but the morphed PCT pattern will not follow the true tropical analysis centers. Third, a possibility exists motion apparent in the clouds because the advective to make use of atmospheric modeling methods to AUGUST 2007 1196 |

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