Vic Klemas

Temperature and size variabilities of the Western Pacific Warm Pool

Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, EI Ni�o—Southern Oscillation events, volcanic activities, and global warming.

Theoretical expression for an ocean internal soliton synthetic aperture radar image and determination of the soliton characteristic half width

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.

Statistical and dynamical analysis of internal waves on the continental shelf of the Middle Atlantic Bight from space shuttle photographs

By interpreting two space shuttle photographs taken with a Linhof camera on June 8, 1991, a total of 34 internal soliton packets on the continental shelf of the Middle Atlantic Bight are recognized. The internal soliton field has a three-level structure: packet groups with average wavelength of 17.5 km, packets with average wavelength of 7.9 km, and solitons with average wavelength of 0.6 km. Using the finite-depth theory we derive that the maximum amplitude of solitons is 5.6 m, the phase speed is 0.42 m/s, and the period is 23.8 min. The frequency distribution of solitons is triple-peaked at 1.9 × 10−4 Hz, 3.0 × 10−4, and 6.9 × 10−4 Hz. Substituting statistical results of number of solitons in a packet into the fission law, we find that the upper and the lower edges of the shelf break are the primary and the secondary generation sources of internal solitons, respectively. This reveals that the sharp change in the bottom topography is a key condition for the soliton fission or disintegration. Calculations show that the group period of solitons is 12.5 hours coinciding with that of local semidiurnal tides. This fact confirms that the tides are a dominant generation force for internal solitons on the continental shelf.

Coastal lee waves on ERS-1 SAR images

Alternative dark-bright patterns on ERS-1 synthetic aperture radar (SAR) images of the west side of the Taiwan Strait taken on December 8, 1994, were recognized to be the sea surface signature of a coastal lee wave. Such waves are called coastal lee waves because they occur along the lee side of the coast. The coastal lee waves appeared in the form of a wave packet distributed within an offshore band 20–40 km wide. The first packet, which occurred in the northern portion of the observed area, contained six waves with variable wavelengths (defined as the spatial separation between two waves) from 1.7 to 2.7 km. The second packet, in the middle, contained 10 waves with a relatively uniform wavelength of 4.2 km. The third packet, in the southern portion, contained 17 waves with an average wavelength of 2.0 km. The crest lengths were from 20 to 80 km. Local meteorologic parameters observed simultaneously at Fuzhou, China, close to the imaged area, showed an offshore wind of 1.5–3.5 m/s and a land surface air temperature of 19°C, which was 4°C lower than the sea surface temperature (SST). Thus the lower atmospheric boundary conditions at imaging time were very favorable both for generating the land breeze circulation and small wind waves on the sea surface, which are in the Bragg-scattering wavelength band of the C band ERS-1 SAR. A physical model of a three-layer atmosphere was developed in order to explain how the land breeze circulation can generate the coastal lee waves. The results showed that the vertical velocity disturbance caused by the wind convergence at the land breeze frontal zone is of vital importance for the generation of coastal lee waves, and the model gave very good estimates of the processes observed. The SAR imaging mechanisms of the waves were analyzed in detail. The differences between coastal lee waves and ocean internal waves, which appear as similar alternative dark-bright patterns on SAR images, were also discussed.

Nonlinear evolution of ocean internal solitons propagating along an inhomogeneous thermocline

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.

Dynamic interpretation of space shuttle photographs: Deepwater internal waves in the western equatorial Indian Ocean

Visible images of deep-ocean internal waves in the western equatorial Indian Ocean taken by the space shuttle Atlantis during mission STS 44 in 1991 are interpreted and analyzed. The internal waves occurred in the form of a multisoliton packet in which there are about a dozen solitons. The average wavelength of the solitons is 1.8±0.5 km, ranging from 1.1 to 2.6 km. The crest lines are mostly straight and reach as long as 100 km. The distance between two adjacent packets is about 66 km. Using the deepwater soliton theory, we derived that the mean amplitude of the solitons is 25 m, the nonlinear phase speed is 1.7 m/s, and the average period is 18 min. The internal semidiurnal tides are the principal generating mechanism. The oblique collision of two multisoliton packets shown on photograph STS 44-93-103 is examined. The results show that the deep-ocean internal waves obey the general properties of soliton collision. The leading solitons and a few followers exhibit some properties of inelastic collision characterized by a phase shift, and the rest of the solitons exhibit properties of elastic collision under resonance conditions.

Digital orthorectification of space shuttle coastal ocean photographs

Abstract Causes of geometric distortion in space shuttle imagery of targets on the Earths 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...

Remote sensing for the identification of coastal plumes: case studies of Delaware Bay

Two Delaware coastal plume events are studied using various remote sensing data. Satellite images obtained from the Advanced Very High Resolution Radiometer (AVHRR), the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) are processed and enhanced to identify coastal plumes from Delaware Bay. Both visible band and infrared sensors give similar results in terms of the plume boundary. The gradient images of both types of sensors show the twin‐front structure near Cape Henlopen, which is also captured in a Synthetic Aperture Radar (SAR) image. Six consecutive SST images are used to track plume variability due to tidal forcing and the features of the plume front are found to be different between ebb and flood tides. Five consecutive SST images taken during a pronounced upwelling‐favourable wind event show the plume widened and separated offshore, while cooler water upwelled onshore of the separated plume.

A solitary wave packet in the atmosphere observed from space

A group of parallel cloud lines was identified in seven successive space shuttle photographs taken over the Pakistani offshore zone in the northern Arabian Sea on April 29, 1993. There are a total of 19 lines aligned with the length of the leading line longer than 250 km and an average separation distance (wavelength) of 1 km. We suggest that the lines are generated by an atmospheric solitary wave packet characterized by decreases in amplitudes and wavelengths from the front to the rear. These features are comparable with the dnoidal soliton solution to the Korteweg-de Vries (KdV) equation. The land breeze and katabatic flow are proposed as a possible generation mechanism.

Derivation of Delaware Bay tidal parameters from space shuttle photography

The tide-related parameters of the Delaware Bay are derived from space shuttle time-series photographs. The water areas in the bay are measured from interpretation maps of the photographs with a CALCOMP 9100 digitizer and ERDAS Image Processing System. The corresponding tidal levels are calculated using the exposure time annotated on the photographs. From these data, an approximate function relating the water area to the tidal level at a reference point is determined. Based on the function, the water areas of the Delaware Bay at mean high water (MHW) and mean low water (MLW), below 0 m, and for the tidal zone are inferred. With MHW and MLW areas and the mean tidal range, the authors calculate the tidal influx of the Delaware Bay, which is 2.76 x 1O[sup 9] m[sup 3]. Furthermore, the velocity of flood tide at the bay mouth is determined using the tidal flux and an integral of the velocity distribution function at the cross section between Cape Henlopen and Cape May. The result is 132 cm/s, which compares well with the data on tidal current charts.