American Meteorological Society Demo

clone into the dry zone, or because of lower-intensity stratiform precipitation, both of which are detected in the radar but not as prominently in microwave imagery. K at r i na’s i n ner a nd outer eyewalls are well defined in the MIMIC-TC animation, which shows that Katrina’s outer eyewall has a nearly continuous ring of convection (with some breaks in the ring to the south) during landfall on the Mississippi River delta (~0600 UTC). As the FIG. 4. Comparison of (left) MIMIC-TC product with (right) NEXRAD 0.5° storm center moved across elevation radar reflectivity composited from four sites (right) for Hurricane Louisiana and up along the Katrina from 2000 UTC 28 August to 2100 UTC 29 August. Time resoluLouisiana–Mississippi bortion of MIMIC-TC is 15 min; time resolution of radar composite is 7.5 min. der, the convection weakRadar is spatially composited according to the nearest station (marked with ens on the southwestern a magenta cross) to each pixel. The MIMIC-TC product is created from 10 side of the outer eye, but the microwave satellite passes. Labels are as follows: (upper-left label) NHC-renorthern half remains well ported maximum sustained winds ("Vmax"); (upper-right label) the temporal separation from the microwave overpass nearest in time (either before or defined until about 1600 after); (magenta perimeter) radar composite domain; (magenta "+") radar UTC as the storm tracked station positions. across Louisiana and into Mississippi. Likewise, the occurs away from the areas of ice scattering. Also, inner eyewall begins as a closed ring of convection the north-northwestern inner band exhibits a good before landfall, but convection weakens on the southexample of pulsing (discussed in the previous section) west side such that the inner eyewall takes a crescent between 0600 and 1300 UTC. shape around 1000 UTC. Subsequently, the eastern The MIMIC-TC and radar animations for eyewall shows increased convective intensity during Hurricane Katrina (Fig. 4) show another recent case landfall on the Mississippi coast at 1400 UTC before of a major tropical cyclone at landfall. Both products becoming disorganized farther inland. In contrast, capture the arrival of a northern outer band around the coincident radar animation shows intermittent 0000 UTC 29 August 2005, subsequently weakening banding of precipitation around the outer eyewall, from west to east. A second band brings a succes- and it is apparent only after several hours of radar sion of small convective cells (~20 km each in size) animation that this area produces an overall secondto southern Louisiana around 0400 UTC and to the ary maximum of precipitation. Thus, the existence Mississippi coast around 0600 UTC. Many of the and timing of the outer eyewall at landfall is less individual cells in that band are tracked in the radar certain in the radar than in MIMIC-TC. The inner animation, and we note that they have lifetimes of eyewall is well defined in the radar because of its about 2 h, just as with the parameterized depiction continuous localized maximum in precipitation, of the MIMIC-TC product. A large dry slot is appar- and the timing of the southwest weakening during ent in the western sector in both animations starting landfall in Louisiana and the relative strength on around 0900 UTC, but it is larger and grows more the eastern side during landfall in Mississippi are in continuously in MIMIC-TC than in the radar, and agreement with the trends in MIMIC-TC. by 1600 UTC the radar shows precipitation over Lake A more complete representation of an eyewall rePonchartrain (30.2°N, 90.2°W) but MIMIC-TC shows placement cycle (ERC; Fortner 1958; Willoughby et al. no activity. This is either because of advection and 1982) is captured in the MIMIC-TC animation of Hurdispersion of precipitation at lower levels in the cy- ricane Ivan (2004; supplemental animation 4 online 1194 | AUGUST 2007

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