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- Author or Editor: Andrew K. Laing x
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Abstract
Wind data from the European Remote-Sensing Satellite (ERS-1) scatterometer are used to depict wind fields in coastal waters around New Zealand. They include mesoscale detail not resolved by present operational models nor from general ships' data due to the low density of observations. These wind data reveal regions of local wind intensification (low-level jet) associated with the ends of orographic barriers. New Zealand has steep and high orography, which frequently induces orographic lee troughs. The jets are particularly evident streaming over coastal waters beyond the ends of these lee troughs. Using a year of scatterometer data, these jets are identified and characterized. Some necessary conditions for their occurrence are established, namely, the general direction of the flow in relation to orographic features, the threshold stability of the airstream, and the degree of orographic blocking. The formation of these jets requires the Brunt-Väisälä frequency for the lower atmosphere, up to a height commensurate with the height of the orography, to be greater than 0.010–0.012 s−1 depending on the location and the Froude number to be lower than 0.7. The general flow conditions determine the position and direction of the jet. Further. when blocking is strong, the features are more intense. However, the authors are unable to predict the length and breadth from the synoptic situation. Given the limited sampling imposed by the coverage of the ERS-1 scatterometer, it has also not been possible to address conditions for sufficiency.
Abstract
Wind data from the European Remote-Sensing Satellite (ERS-1) scatterometer are used to depict wind fields in coastal waters around New Zealand. They include mesoscale detail not resolved by present operational models nor from general ships' data due to the low density of observations. These wind data reveal regions of local wind intensification (low-level jet) associated with the ends of orographic barriers. New Zealand has steep and high orography, which frequently induces orographic lee troughs. The jets are particularly evident streaming over coastal waters beyond the ends of these lee troughs. Using a year of scatterometer data, these jets are identified and characterized. Some necessary conditions for their occurrence are established, namely, the general direction of the flow in relation to orographic features, the threshold stability of the airstream, and the degree of orographic blocking. The formation of these jets requires the Brunt-Väisälä frequency for the lower atmosphere, up to a height commensurate with the height of the orography, to be greater than 0.010–0.012 s−1 depending on the location and the Froude number to be lower than 0.7. The general flow conditions determine the position and direction of the jet. Further. when blocking is strong, the features are more intense. However, the authors are unable to predict the length and breadth from the synoptic situation. Given the limited sampling imposed by the coverage of the ERS-1 scatterometer, it has also not been possible to address conditions for sufficiency.
Abstract
The mean dynamic height of the ocean surface is estimated along a subsatellite track of TOPEX/Poseidon crossing the East Auckland Current system northeast of New Zealand. Repeated hydrographic surveys along the track, together with surface elevation anomalies deduced from TOPEX altimeter data, enable four independent estimates of the mean dynamic height. From these estimates a more stable mean is calculated in which the uncertainty is estimated as less than 5 cm. The result can be applied as a reference profile for calibrating a long series of TOPEX passes so that cross-track geostrophic currents can be calculated. The scatter in the individual estimates indicates sufficient sampling variability to caution against using single hydrographic surveys as a basis for calibrating the satellite data.
Abstract
The mean dynamic height of the ocean surface is estimated along a subsatellite track of TOPEX/Poseidon crossing the East Auckland Current system northeast of New Zealand. Repeated hydrographic surveys along the track, together with surface elevation anomalies deduced from TOPEX altimeter data, enable four independent estimates of the mean dynamic height. From these estimates a more stable mean is calculated in which the uncertainty is estimated as less than 5 cm. The result can be applied as a reference profile for calibrating a long series of TOPEX passes so that cross-track geostrophic currents can be calculated. The scatter in the individual estimates indicates sufficient sampling variability to caution against using single hydrographic surveys as a basis for calibrating the satellite data.
Abstract
Mesoscale lows are observed off the central west coast, South Island, New Zealand. These features are evidenced in pressure dips measured at a buoy moored about 50 km off the west coast. They do not appear in measurements from coastal stations. Wind data at the buoy show complex variations sometimes consistent with the passage of cyclonic vortices in the flow. Further, wind data from satellite scatterometers often indicate high spatial variability near the buoy at the time of these pressure dips, and satellite imagery depicts cloud movements consistent with small-scale cyclonic circulations near the coast. These features are often observed in the cool air after the passage of a trough or front.
Abstract
Mesoscale lows are observed off the central west coast, South Island, New Zealand. These features are evidenced in pressure dips measured at a buoy moored about 50 km off the west coast. They do not appear in measurements from coastal stations. Wind data at the buoy show complex variations sometimes consistent with the passage of cyclonic vortices in the flow. Further, wind data from satellite scatterometers often indicate high spatial variability near the buoy at the time of these pressure dips, and satellite imagery depicts cloud movements consistent with small-scale cyclonic circulations near the coast. These features are often observed in the cool air after the passage of a trough or front.
