Showing papers by "Quanan Zheng published in 1997"

Centroid Motion of the Western Pacific Warm Pool during Three Recent El Niño–Southern Oscillation Events

Abstract: The centroid motion of the Western Pacific warm pool for 1982–83, 1986–87 and 1991–93 El Nino–Southern Oscillation events was investigated by analyzing satellite multichannel sea surface temperature and satellite pathfinder sea surface temperature data in conjunction with wind data from The Florida State University. The authors found that the direction of motion of the warm pool’s center changes shortly before the onset of a new El Nino event and that this change was quite different during the 1991–93 El Nino than during the 1982–83 and 1986–87 El Nino events. The possible cause of these changes and differences may be the El Nino–related wind pattern shifts in the western equatorial Pacific Ocean before and during the events, and the seasonal phase-lock of the El Nino events.

Seasonal and interannual variability of atmospheric convergence zones in the tropical Pacific observed with ERS-1 scatterometer

Abstract: Monthly images of atmospheric convergence zones in the tropical Pacific were produced with 1992–1994 ERS-1 scatterometer wind vectors. From the images, the position, width, and intensity of the convergence zones can be determined. Latitude-time sections of ocean surface wind divergence show that the summer position of the ITCZ in the eastern Pacific during the observed period exceeded the normal position northward by 3°–6° latitude, and the annual cycle in the western Pacific for 1994 was quite weak, implying a persistently unusual case.

Digital orthorectification of space shuttle coastal ocean photographs

Abstract: Causes of geometric distortion in space shuttle imagery of targets on the Earth's surface are analysed. A mathematical model formulating the geometric distortion caused by the incidence angle and the local azimuth angle are derived, and the corresponding image processing scheme for orthorectification is developed. The method is used for rectifying two sequential space shuttle photographs of continental shelf waters off the coast of south-west Africa taken by the space shuttle Atlantis during mission STS-36 in March 1990. The results indicate that mismatches between coastline images in unrectified photographs and a standard map have been almost eliminated in the rectified photographs, and the two photographs also match each other very well. Application of the spatial Fourier transform to oceanic internal wave packet signals at a selected test site yields directional wavenumber spectra, from which components of the wave field, the dominant wavelength, and propagation directions are determined. Comp...

The effects of water temperature on radar scattering from the water surface : An X-band laboratory study

Abstract: The surface tension is a restoring force, the viscosity is a dissipative resistance for microwave scattering gravity-capillary waves on the ocean surface. Both the surface tension and viscosity are water temperature dependent: therefore, it is reasonable to expect the surface wave spectral density in the centimeter range to be temperature dependent. Bragg scatter is wave intensity dependent; therefore, the radar cross section of the ocean surface should also be temperature dependent. In order to verify this inference, a laboratory experiment for X-band backscattering from a rough water surface with varied water temperature was conducted in the absence of wind. Our data show a monotonic increase of the radar cross section with the water temperature. Based on our data, a semi-analytic model is proposed to relate the water surface temperature and the Normalized Radar Cross Section (NRCS) of the water surface as follows: Formula. Math. The semi-analytical model can be used to improve the scatterometer wind algorithm as well as SAR image interpretation, in general.

Dynamic Analysis of Ocean Internal Waves Using Space Shuttle Data

Abstract: : Long-term goals of the project are to develop suitable techniques for extracting quantitative data and information on ocean internal waves from space shuttle photographs and SIR-C images, to determine statistical features of the wave packet structures, and to analyze the generation, propagation, and collision of the waves, as well as the effects of boundary conditions.

Solitary coastal lee waves observed from space

Abstract: Alternating dark-bright patterns along the coast on Landsat MSS and the ERS-1 SAR images were recognized to be the image of a coastal lee wave Such waves are called coastal lee waves because they occur along the lee side of the coast The first case was noted in the offshore area of the Delaware Bay in the middle Atlantic Bight shown as a wave- like cloud pattern on MSS images taken in December 14, 1975 The second case was detected by the ERS-1 SAR shown on the image of the Taiwan Strait taken on December 8, 1994 The average wavelength is 2 km, ranging from 03 km to 42 km The crest lines with length from 20 km to more than 100 km are generally parallel to the coastline The horizontal distribution range is a band 20 km wide, 20-100 km offshore The vertical extent of the disturbance reaches from the ocean surface to the top of cumulus The waves manifest solitary characteristics The seasonal land-breeze circulation is being proposed as a major generation mechanism for the observed lee waves