  We present theoretical wavelength-dependent transit light curves for the
giant planet HD209458b based on a number of state of the art 3D radiative
hydrodynamical models. By varying the kinematic viscosity in the model we
calculate observable signatures associated with the emergence of a
super-rotating circumplanetary jet that strengthens with decreased viscosity.
We obtain excellent agreement between our mid-transit transit spectra and
existing data from Hubble and Spitzer, finding the best fit for intermediate
values of viscosity. We further exploit dynamically driven differences between
eastern and western hemispheres to extract the spectral signal imparted by a
circumplanetary jet. We predict that: (i) the transit depth should decrease as
the jet becomes stronger; (ii) the measured transit times should show timing
offsets of up to 6 seconds at wavelengths with higher opacity, which increases
with jet strength; (iii) wavelength-dependent differences between ingress and
egress spectra increase with jet strength; (iv) the color-dependent transit
shape should vary more strongly with wavelength for stronger jets. These
techniques and trends should be valid for other hot Jupiters as well.
Observations of transit timing offsets may be accessible with current
instrumentation, though the other predictions may require the capabilities JWST
and other future missions. Hydrodynamical models utilized solve the 3D
Navier-Stokes equations together with decoupled thermal and radiative energy
equations and wavelength dependent stellar heating.
