2D.1a
Satellite Applications for Tropical Wave/Tropical Cyclone Tracking (Formerly Paper P1.19)
Jason P. Dunion, NOAA/AOML/HRD and Univ. of Miami, Miami, FL; and C. S. Velden
Recent collaborative efforts between NOAA's Hurricane Research Division (HRD) and the Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS) have resulted in the development of several new satellite-derived products designed for tropical cyclone applications. These products utilize geostationary satellite imagery and satellite winds produced at UW-CIMSS which are made available in real-time.
Low-level (600-925 hPa) cloud-drift winds produced from the 3.9 µm shortwave infrared (SWIR) channel on GOES-8/10 are being developed to compliment with nighttime coverage, the visible winds currently being produced operationally at NOAA/NESDIS. This near-infrared channel provides a cleaner atmospheric window (compared to the operational 11 µm longwave IR channel) for superior low-level cloud detection at night. By enhancing the brightness temperatures in the SWIR images prior to their input into the UW-CIMSS wind algorithms, the flat gradients that are characteristic of this channel can be sharpened. This typically produces a 40-60% improvement in low-level cloud detection over identical non-enhanced SWIR wind runs.
A mid-level shear product is being developed to depict the vertical shear characteristics in the middle to lower troposphere. A typical deep layer shear calculation does not always represent the most effective method for determining potentially negative shearing conditions in the environment of a tropical system. Weak tropical disturbances are often too shallow to be extensively impacted by upper tropospheric winds and the strong easterly low-level wind surges associated with the Saharan Air Layer (SAL) are usually confined to the 500-850 hPa layer. The mid-level shear product calculates vertical shear using the 400-600 hPa layer minus the 700-925 hPa layer and may provide useful information to forecasters monitoring weaker tropical systems as well as tropical cyclones that are in proximity to the SAL.
The Saharan Air Layer (SAL) is often associated with a low-level easterly surge centered at about 700 hPa that originates over the northwest African continent. This westward advancing dust and associated wind surge is detectable using GOES-8 split window satellite imagery. There are several negative effects associated with the SAL outbreaks. First, the emission of longwave IR radiation by the dust silicates that typically concentrate at 700 hPa acts to warm this layer and enhance the tropical inversion, surpressing convective activity. Second, the dust acts as a tracer for the SAL low-level wind surge that can greatly increase the local atmospheric vertical shear. Lastly, the dust also acts as a tracer for dry, stable air associated with the SAL that can surpress local convection, making the environment non-conducive to tropical cyclone formation.
A deep layer mean environmental steering product has been developed for use in the northern hemisphere Atlantic and Pacific basins. These wind analyses depict the environmental flow for selected tropospheric layer-means. Based on previous studies (Atlantic basin), the depth of this layer is correlated with the TC steering layer, and generally increases with increasing TC intensity. These analyses are strongly influenced by high-density, multispectral satellite-derived wind information. This product has applications as a tool for approximating the current and short-term environmental steering flow for tropical cyclones of varying intensities in the Atlantic and Pacific basins.
Session 2D, Tropical Cyclone Motion (Parallel with Sessions 2A, 2B, & 2C)
Monday, 29 April 2002, 2:00 PM-3:15 PM
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