The Impact of Idealized Terrain on Upstream Tropical Cyclone Track

Tropical cyclones (TCs) encountering the terrain of Taiwan usually experience prominent track deflection, resulting in uncertainty in TC track forecasts. The underlying mechanisms of TC deflection are examined to better understand the pattern of TC tracks under various flow regimes. In this study, idealized experiments are carried out utilizing the Advanced Research version of the Weather Research and Forecasting (WRF) Model. This study investigates the motion of a TC that is deflected southward while moving westward toward an idealized terrain similar to Taiwan. An analysis of both the flow asymmetries and the potential vorticity tendency (PVT) demonstrates that horizontal advection contributes to the southward movement of the TC. The track deflection is examined in two separate time periods, with different mechanisms leading to the southward movement. Changes in the background flow induced by the terrain first cause the large-scale steering current to push the TC southward while the TC is still far from the terrain. As the TC approaches the idealized topography, the role of the inner-core dynamics becomes important, and the TC terrain-induced channeling effect results in further southward deflection. Asymmetries in the midlevel flow also develop during this period, in part associated with the effect of vertical momentum transport. The combination of the large-scale environmental flow, the low-level channeling effect, and asymmetries in the midlevel flow all contribute to the southward deflection of the TC track.

Design of a 2 GHz Linear-in-dB Variable-Gain Amplifier with 80-dB Gain Range

A broadband linear-in-dB variable-gain amplifier (VGA) circuit is implemented in 0.18 μm SiGe BiCMOS process. The VGA comprises two cascaded variable-gain core, in which a hybrid current-steering current gain cell is inserted in the Cherry-Hooper amplifier to maintain a broad bandwidth while covering a wide gain range. Postlayout simulation results confirm that the proposed circuit achieves a 2 GHz 3-dB bandwidth with wide linear-in-dB gain tuning range from −19 dB up to 61 dB. The amplifier offers a competitive gain bandwidth product of 2805 GHz at the maximum gain for a 110-GHz ftBiCMOS technology. The amplifier core consumes 31 mW from a 3.3 V supply and occupies active area of 280 μm by 140 μm.

Simulation of Movement of Oil Slicks in the Strait of Georgia Using Simple Atmosphere and Ocean Dynamics

ABSTRACT Hydrodynamical techniques were used to investigate the movement of oil slicks in the Strait of Georgia by assuming that the oil moves with the current and not with the wind. The divergence of the isobaths near Alden Bank probably makes the current branch while that southeast of Pt. Roberts narrows and intensifies the current. The effect of mutual interaction among several slicks both with and without a steering current such as a tidal or wind-generated current is found to be important in determining their trajectories. For oils with large viscosities, an oscillatory tidal current could give rise to an unstable situation in which the oil spreads in the form of long lines radiating out from the spill similar to the spokes in a bicycle wheel. Stratification of the water causes the oil plume to bifurcate and due to this phenomena, even if one branch of the plume carrying the oil goes away from the coast, the second branch carries oil to the coast.

Verification of JNWP-Unit Hurricane and Typhoon Forecasts for 19591

During the 1959 season for tropical storms in the Northern Hemisphere, Joint Numerical Weather Prediction (JNWP) Unit computed operationally one or more forecast tracks for 11 hurricanes and tropical storms and 11 typhoons. The 500-mb barotropic forecast flow with the tropical vortex eliminated from the initial 500-mb analysis was employed as the steering current in obtaining these forecasts. A summary of 1959 forecasts and a table of verification of JNWP hurricane forecasts for the years 1956 through 1959 are presented. The improvement and deterioration in forecasts from one year to the next are discussed in terms of sample size, operational changes, and analysis and forecasting techniques specifically designed for forecasting trajectories of tropical cyclones.

Further Studies of the Movement and Formation of Hurricanes and Their Forecasting

At first the relation between the motion of tropical storms and the speed of the steering current is investigated quantitatively. This necessitates definition of the steering current along all space axes and time. The result is that the zonal component of motion of storms on the average equals the zonal component of the steering current. There is some scatter about the linear regression line. The following parts deal with formation of tropical storms. Earlier work on the relation between motion of the long wave train in the westerlies and development of hurricanes is extended and it is shown that progression of the long waves very frequently precedes deepening. A synoptic example shows the three-dimensional structure of the atmosphere and its changes with time.