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MIMIC-IR (Morphed Integrated Microwave Imagery at CIMSS, with Infrared) |
The IR imagery is not morphed. The IR animation is composed of a series of geostationary satellite images nearest in time to the display time. Sometimes the IR animation appears "jerky" because it does not always update as frequently as the PCT product.
The PCT morphing algorithm needs to define a center of rotation in the PCT images, and so the algorithm's center moves directly between PCT-defined center locations. However, the IR captures additional displacement of the eye, either because of vertical wind shear, errors in parallax correction, or image navigation error. The eye in the IR also undergoes more complicated motion through two mechanisms - trichoidal oscillation and short-lived departures from the interpolated path over short (approx. 1-12 hour) time periods.
For the foreseeable future, the MIMIC-IR product will require more interpretation from the end-user (that's you!) to be at its most effective. When the PCT eye position and the IR eye position do not exactly match, the end-user must mentally adjust the layer that is out of place. For example, if the eye in the PCT layer is fixed in the center while the eye in the IR revolves within a small space around the center, the end-user should picture the PCT eyewall revolving with the IR eye.
During occasional "blackout periods" in IR temporal coverage (often lasting several hours), then the "nearest image" used by the algorithm remains the nearest image for several hours. The display in the MIMIC-IR algorithm will always keep the IR imagery true to its navigation, so the lat/lon positions in the image are always the same as long as the image is shown. However, as the frame of reference moves along, the IR image will drift away as it sticks to its original position.
It would seem that moving the IR image along with the frame of reference would fix this problem. However, if the IR image were adjustable in this way, then it would cease to be a good spatial reality-check for the PCT product, which is its most important role.
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The morphing algorithm moves microwave signatures of convective cells within a frame of reference that follows the path of the storm center. This is an effective advection scheme in some cases but not in others. The most common problem with this scheme is that some convective cells are fairly stationary (shown in the IR layer), but the algorithm advects the PCT signal away from the true position. (In practice, this appears as the PCT signal advecting through the IR cell, as it moves toward the IR cell before the time of the nearest PCT image and away from the IR cell after the time of the nearest PCT image.) |
MIMIC and MIMIC-IR have a simple parallax correction algorithm. The position of the microwave imagery is shifted on the assumption that the observed structures are uniformly 10 km high. This creates an overcorrection for low-lying features, particularly coastlines, but minimizes the position error on the eyewall, which is the most important feature.
The position of the infrared imagery is shifted on the assumption that the observed structures are uniformly 16 km high, for the same reasons.
Abbreviation for "infrared". In the MIMIC-IR imagery, geostationary
longwave infrared channels (~10.7 um) are used.
"Polarization Corrected Temperature". This derived quantity has been shown to vary inversely with precipitation. More information is provided in a tutorial from the Naval Research Laboratory Monterey Marine Meteorology Division.
Abbreviation for "brightness temperature", normally presented in
units of degrees Kelvin.
In tropical cyclones, this is the phenomenon of a small vortex
revolving inside a larger vortex. If the motion of the eye has
trichoidal oscillation, then in high temporal resolution imagery it
appears to be rolling inside a larger circle. (A quirky by very
effective comparison is to the motion of a pencil in a Spirograph.)