Showing papers by "Quanan Zheng published in 2001"
TL;DR: The upwelling along the Java-Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate as discussed by the authors, which migrates westward and toward the equator during the southeast monsoon (June to October).
Abstract: Upwelling along the Java-Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate The upwelling center with low sea surface temperature migrates westward and toward the equator during the southeast monsoon (June to October) The migration path depends on the seasonal evolution of alongshore winds and latitudinal changes in the Coriolis parameter Upwelling is eventually terminated due to the reversal of winds associated with the onset of the northwest monsoon and impingement of Indian Ocean equatorial Kelvin waves Significant interannual variability of the Java-Sumatra upwelling is linked to ENSO through the Indonesian throughflow (ITF) and by anomalous easterly wind During El Nino episodes, the Java-Sumatra upwelling extends in both time (into November) and space (closer to the equator) During El Nino (La Nina), the ITF carries colder (warmer) water shallowing (deepening) thermocline depth and enhancing (reducing) upwelling strength
334 citations
TL;DR: In this article, the authors derived a theoretical model of a radar image for a Korteweg-de Vries type ocean internal soliton and validated the model using ocean internal wave signals taken from ERS-1 SAR and RADARSAT SAR images.
Abstract: This paper deals with the development of techniques for satellite synthetic aperture radar (SAR) ocean image interpretation. We derived a theoretical model of a radar image for a Korteweg-de Vries type ocean internal soliton and validated the model using ocean internal wave signals taken from ERS-1 SAR and RADARSAT SAR images. The results indicate that the model perfectly simulates ocean internal soliton signatures with double-sign variations of radar backscatter. On the basis of the model, we developed the curve fitting method and the peak-to-peak method for determining the internal soliton characteristic half widths, which then were used to calculate the internal soliton amplitudes. The test results indicate that ocean internal soliton amplitudes derived by the two methods agree with in situ data acquired on the Portuguese Continental Shelf and in the South China Sea with reasonable accuracy. The role that wind fields play in ocean radar remote sensing was also analyzed. Finally, the modulation ratio of ocean internal waves on radar images was quantitatively estimated.
128 citations
TL;DR: In this paper, Tappert et al. analyzed the evolution of ocean internal solitary waves passing over a seamount in the Gulf of Aden and found that a surprisingly sharp recess of an internal solitary wave packet, imaged by the space shuttle Discovery, is a signature of spatial phase delay caused by thermocline shoaling over the seamount.
Abstract: Measurements of the upper ocean thermal structure show that on the continental shelves the thermocline depth may shoal or deepen generally depending on the bottom topography. Thermocline shoaling and deepening cause changes in the phase speeds of internal waves as described by linear wave theories. On the other hand, the ocean area where internal waves have variable phase speeds may be treated as a dynamically inhomogeneous medium. In this case, theories of nonlinear dispersive wave propagation in inhomogeneous media developed by Tappert and Zabusky [1971] may stand. We used these theories to analyze the evolution of ocean internal solitary waves passing over a seamount in the Gulf of Aden. The results indicate that a surprisingly sharp recess of an internal solitary wave packet, imaged by the space shuttle Discovery, is a signature of spatial phase delay caused by thermocline shoaling over the seamount. Soliton fission due to thermocline shoaling was also observed in the imagery. The observed number of transmitted solitons over the seamount agrees with theoretical predictions. Relative soliton amplitudes measured from the imagery also agree qualitatively with predictions.
35 citations
TL;DR: In this article, the authors observed oil slicks along a ship wake in the northern Arabian Sea and determined that turbulent diffusion and wind drag were the dominant forcing for the oil slick spreading.
21 citations
TL;DR: In this article, the authors examined a group of wave-like cloud patterns that occurred along the coast of Texas on a National Oceanic and Atmospheric Administration satellite advanced very high resolution radiometer IR images taken on January 22, 1999.
Abstract: We examine a group of wave-like cloud patterns that occurred along the coast of Texas on a National Oceanic and Atmospheric Administration satellite advanced very high resolution radiometer IR images taken on January 22, 1999. These wave-like cloud patterns were interpreted to be signatures of a coastal lee wave packet on the basis of simultaneous field observations and theories developed by Zheng et al. [1998a]. The wave packet contains 13 waves with crest lines generally parallel to the coastline. The lengths of leading wave crest lines are longer than 500 km. The average wavelength is 9.5 km, ranging from 6.2 to 14.7 km. The width of the horizontal distribution band of the wave packet is as wide as 113 km. This case represents the most energetic coastal lee wave packet that has ever been reported.
20 citations
TL;DR: In this paper, the vector empirical orthogonal function (VEOF) method was used to analyze ocean surface winds derived from NSCAT, QuikSCAT and ERS-1/2 scatterometer observations during a period from January 1992 to April 2000.
Abstract: Ocean surface winds derived from NSCAT, QuikSCAT and ERS-1/2 scatterometer observations during a period from January 1992 to April 2000 were analyzed using the vector empirical orthogonal function (VEOF) method. With the boreal winter and summer oscillation, the first VEOF is dominated by the Indian and East Asian monsoons and also shows an annual cycle of the trade winds. The second VEOF represents the boreal autumn and spring oscillation, and reveals a transition state between winter and summer. The third VEOF indicates the wind variability associated with El Nino Southern Oscillation (ENSO) events, because the temporal mode has a high correlation coefficient of 0.8 with the Southern Oscillation Index (SOI). Furthermore, the third mode reveals the teleconnection of the Indian monsoon and wind variability over high latitude oceans, such as the Aleutian Low system, with ENSO events.
13 citations
TL;DR: In this paper, the vector empirical orthogonal function (VEOF) method was used to process the wind data set and extract principal modes of the wind fields, which can lead to better understanding of ENSO events.
Abstract: The variation of the Walker circulation is closely related to the onset of El Nino-Southern Oscillation (ENSO) events [Kousky, 1984], so observing the Walker circulation can lead to better understanding of ENSO events. Wind data from the NASA Scatterometer (NSCAT), Quick Scatterometer (QuikSCAT), and European Remote Sensing Satellite-1/2 (ERS-1/2) were merged into one data set in a 1°×1° grid covering a period from January 1992 to December 2000. The study region was confined to the tropical oceans between 20°S and 20°N. The vector empirical orthogonal function (VEOF) method [Hardy and Walton, 1978] was used to process the wind data set and extract principal modes of the wind fields.
5 citations
TL;DR: In this article, a global database on internal waves has been developed at the center with support from ONR and NASA, and is accessible on the Internet The database includes visible and radar imagery, including digitally orthorectified images were used for dynamic and statistical analysis of internal waves.
Abstract: Space shuttle photographs and satellite radar (SAR) images provide an excellent view of high‐contrast ocean features such as internal waves, fronts, eddies, oil slicks, and cloud patterns which contain the signatures of atmospheric processes Since ocean internal waves generate local currents which modulate surface wavelets and slicks, we have been able to detect packets of internal waves in space shuttle photographs and radar imagery of the Atlantic, Pacific, and Indian Oceans A global database on internal waves has been developed at our center with support from ONR and NASA, and is accessible on the Internet The database includes visible and radar imagery To test the database, digitally orthorectified images were used for dynamic and statistical analysis of internal waves In the deep ocean we found the wavelength distribution to be Gaussian while in the coastal ocean it is Rayleigh Results have also been applied to non‐linear evolution studies of ocean internal waves, atmospheric solitary
3 citations
30 Sep 2001
TL;DR: In this article, the authors developed a global database of ocean internal waves observed primarily from spacecraft, which can be used for various purposes including understanding the statistical properties of internal waves and upper ocean dynamics in any ocean area of interest.
Abstract: : Our long-term goal is to develop a global database of ocean internal waves observed primarily from spacecraft. This database will be publicly accessible and can be used for various purposes including understanding the statistical properties of internal waves and upper ocean dynamics in any ocean area of interest.