Do Frontal Cyclones Change Size? Observed Widths of North Pacific Lows

Abstract

Wavelet transforms in the longitudinal and latitudinal directions are applied to sea level pressure data for 12 extratropical cyclones. Each low is tracked over time from a stage of small amplitude to a stage of large amplitude. The wavelet transform provides a quantitative, localized estimate of the size of the low pressure. Separate one-dimensional transforms are taken in the longitudinal and latitudinal directions; these are averaged to reduce scale variations created as circular asymmetries rotate around a low center. On average, the size of the lows increases such that the diameter doubles over a 4-day period. These results pass a standard ?f test? with greater than 99% confidence. Some implications for theoretical studies are included.