JONSWAP spectrum

The JONSWAP spectrum is a fetch-limited wave energy spectrum from the 1973 Joint North Sea Wave Project, formed by multiplying a Pierson-Moskowitz base by a peak-enhancement factor. It is written S(omega) = alpha g squared omega-to-the-minus-5 times exp of minus 1.25 times (omega_p over omega) to the fourth, all multiplied by gamma raised to the exponent r, where r = exp of minus (omega minus omega_p) squared over (2 sigma squared omega_p squared). The peak-enhancement factor gamma has a mean value of 3.3 (range about 1 to 7), and sigma is 0.07 for omega at or below omega_p and 0.09 above it. With gamma = 1 it reduces to Pierson-Moskowitz. It sharpens the peak for growing, fetch-limited seas.