In addition, the new model can be readily extended to include other pressures such as an electric stress. Raindrop turquoise is a recently recognized and characterized pattern with a saturated coloration resembling raindrops. In contrast to earlier models of raindrop shape for the oblate spheroid response to gravity (Green, Beard) or the perturbation response to the aerodynamic pressure for a sphere (Imai, Savic, Pruppacher and Pitter), the present model provides the appropriate large amplitude response to both the hydrostatic and aerodynamic pressures modified for distortion. Coefficients are provided for computing raindrop shape as a cosine series distortion on a sphere. A close match was found between model shapes and profiles obtained from photos of water drops for diameters up to 5 mm. The model yields the peculiar asymmetric shape of raindrops: a singly curved surface with a flattened base and a maximum curvature just below the major axis. Instead, because of the way they stretch as they fall, they look a lot like a pair of earmuffs, with two drops of water to either side, connected by a thin band of water. The largest raindrops 4.5 millimeters and above don’t resemble drops at all. Model results provide bounds on the axis ratio of raindrops with an uncertainty of about 1% and very good agreement with extensive wind tunnel measurements for moderate to large water drops. At three millimeters, they distort even more as they fall, forming a kidney shape. The shape was closed at the lower pole by adjusting either the pressure drag or the drop weight to achieve an overall force balance. The drop shape was calculated by integration from the upper pole with the initial curvature determined by iteration on the drop volume. In contrast to earlier models of raindrop shape for the oblate spheroid. The equilibrium shape of raindrops has been determined from Laplace's equation using an internal hydrostatic pressure with an external aerodynamic pressure based on measurements for a sphere but adjusted for the effect of distortion. Model results provide bounds on the axis ratio of raindrops with an uncertainty. Introduction usual method of calculating terminal velocities, then, is equivalent to the following indirect procedure.
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