In order to examine gravity wave characteristics over the ocean, we conducted a radiosonde observation campaign to scan the stratosphere meridionally over the middle Pacific with Hakuho-maru research vessel operated by the Ocean Research Institute, University of Tokyo. Seventy vertical profiles of temperature, winds, and humidity were successfully obtained over a wide latitude range of 28¿N to 48¿S with an interval of 1 degree. Gravity wave energy and vertical wavenumber spectra were examined as a function of latitude. Gravity wave energy is maximized in the tropical region where the convection is active and in the middle latitude region where the subtropical westerly jet is situated. The wave energy in the tropical region is greater than the climatology based on operational radiosonde observation over land regions. The gravity wave amplitude does not necessarily increase with altitude, in contradiction to simple vertical propagation. The latitudinal distribution of wave energy rather suggests that gravity waves propagate meridionally toward higher latitudes. An interesting feature is that a wave packet having large horizontal wind and temperature amplitudes is observed continuously over 7 days in the latitudinal region extending 26 degrees. Results of hodograph analysis indicate that the wave packet is due to an inertia-gravity wave with horizontal and vertical wavelengths of about 1800 km and 4--5km, respectively. This inertia-gravity wave is likely generated in association with vigorous convection in the Intertropical Convergence Zone (ITCZ) in the Northern Hemisphere and propagated southward interhemispherically. The results in this study show that there are strong nonstationary gravity wave sources over the ocean. The importance of meridionally propagating gravity waves is discussed.