Weather recursive · not sovereign

Hurricane

A vortex whose own winds pull the heat out of the ocean that keeps those winds going.

A hurricane is a loop between wind and sea. The wind speeds evaporation from the ocean surface; the water vapor rises and condenses in the eyewall, releasing heat; the heat lowers the pressure at the center, and the lower pressure drives the wind harder. The storm’s own winds fetch its fuel. The ocean sets a ceiling on how strong the loop can get, called the potential intensity. Wind shear and dry air bleed it. Take away the warm ocean, at landfall, and the loop starves.

One Storm, Seen From Above

1,500 km across · ocean to the right, coast to the left

maximum wind—

strength—

inner-core moisture m (0 to 1)—

potential intensity now (m/s)—

position—

storm age—

intensifying

Intensity follows Emanuel’s two-equation model (2017); the map is drawing. Two simplifications: the cooling a storm stirs up in the ocean beneath itself is left out, and the track is a straight line you trigger. Spiral bands, the eye (gold ring, shown from hurricane strength) and the spin, drawn 40 times slower than true, are derived from wind and moisture, not simulated. The wind is the model’s maximum circular wind, so the category shown is approximate: official categories use 1-minute sustained wind, which includes the storm’s motion. Time is the solver’s clock, 3 model hours for each real second.

The Loop, in Two Equations

Emanuel (2017), with the ocean-cooling term switched off

dV/dt = ½(C_D/h)[ b V_p² m³ − (1 − c m³) V² ]
dm/dt = ½(C_D/h)[ (1 − m) V − 2.2 S m ]
V wind · m inner-core moisture · V_p potential intensity · S shear
C_D = 1.2×10⁻³, h = 1400 m, b = 0.57, c = 0.43

The loop is written into the second equation. The term (1 − m) V says the wind itself moistens the core: the faster the wind, the faster the sea gives up water. The term m³ in the first equation says that moisture drives the wind. Shear, 2.2 S m, dries the core out. Potential intensity V_p is the ceiling the ocean’s warmth and the air above it allow; over the warmest tropical oceans it can exceed 80 m/s, and over cool water it falls sharply. The model sets it to zero over land, as Emanuel’s does.

Why It Reads as Recursive

an authored reading, not a measurement

The storm releases its own driving energy: its winds fetch the heat that powers them. That is the test on the Weather page, and it places the hurricane with the thunderstorm, not with the attractlets. Press Steer it ashore and the loop starves.

This is the card where “not sovereign” is least secure. A mature hurricane comes back from dry air on its own, and it builds its own eyewall out of raw, moist inflow. Whether that eyewall is a self-made, identity-bearing boundary in the sense of Condition 3 of the sovereignty test is an open question, left open here along with base versus coordination.

This panel is not the storm. The program is an attractlet model under § 7.4, as on the Lorenz page.

The Shape of the Basin

measured on this model, from its default seed

The basin is the set of tropical disturbances that, over warm enough ocean and in weak wind shear, spin up into a warm-core vortex. In this model, starting from its seed (15 m/s wind, core moisture 0.7), that means a potential intensity of about 50 m/s or more and shear of 6 m/s or less. At shear of 7 m/s the same seed never reaches hurricane strength.

Inside the basin, the storm comes back. Press Inject dry air on a mature storm at the default settings: the core moisture halves, the wind falls from about 52 to 35 m/s, and within about three days the storm is back near its ceiling.

Outside it, the storm does not. Press Steer it ashore: at landfall the potential intensity drops to zero, and the wind halves in about 17 hours.

Emanuel, K. (2017). A fast intensity simulator for tropical cyclone risk analysis. Natural Hazards, 88(2), 779–796. doi:10.1007/s11069-017-2890-7

← Back to Weather