The use of satellite-derived Total Precipitable Water (TPW) imagery for identifying Saharan Air Layers affecting tropical cyclones

This study uses Special Sensor Microwave/Imager (SSM/I) derived total precipitable water (TPW) imagery to identify Atlantic basin tropical cyclones (TCs) in close proximity to Saharan Air Layers (SALs) and compares this method with the GOES multipectral SAL imaging techniques developed by Dunion and Velden (2004). While TPW products have low temporal resolution, they can provide additional details about SAL and TC structure, such as asymmetries and moisture gradients that aid in interpreting SAL and TC interactions. Preliminary analyses of TPW imagery from this study reveal that many TCs have been in close proximity to SALs during some phase of their life cycle with different outcomes. Some TCs imbedded within or near SALs showed no discernable effect on their development and intensification, while others remained relatively weak or dissipated, perhaps as a result of the interaction with the SAL. TPW imagery, able to resolve moisture levels beneath cirrus clouds, reveals that sometimes the low humidity SAL air surrounding TCs is being entrained in the outer circulation bands without penetrating the TC inner circulation core. In other cases, the dry air spirals close to the center. Comparisons of the SAL and TC structure from TPW and GOES imagery will be discussed and some pertinent case studies will be described.