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- Author or Editor: Mark Lander x
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Abstract
El Niño-Southern Oscillation (ENSO)-related variations in the observed character (e.g., annual storm totals, preferred genesis region, etc.) of the tropical cyclone activity in the western North Pacific are sought. With respect to annual storm totals, no ENSO signal is found; with respect to genesis region, a strong relationship is found between ENSO indices and the zonal displacement of the annual mean genesis locations. ENSO indices during the first half of the calendar year were found to be weakly predictive of the number and genesis locations of tropical cyclones occurring from July through December.
Abstract
El Niño-Southern Oscillation (ENSO)-related variations in the observed character (e.g., annual storm totals, preferred genesis region, etc.) of the tropical cyclone activity in the western North Pacific are sought. With respect to annual storm totals, no ENSO signal is found; with respect to genesis region, a strong relationship is found between ENSO indices and the zonal displacement of the annual mean genesis locations. ENSO indices during the first half of the calendar year were found to be weakly predictive of the number and genesis locations of tropical cyclones occurring from July through December.
Abstract
The evolution of the pattern of the deep convective cloud is presented for three selected cases of tropical cyclone twins symmetrical with respect to the equator. In each case, the pattern evolution is similar and can be separated into four distinct stages.
Abstract
The evolution of the pattern of the deep convective cloud is presented for three selected cases of tropical cyclone twins symmetrical with respect to the equator. In each case, the pattern evolution is similar and can be separated into four distinct stages.
Abstract
This paper describes the character and evolution of the low-level wind, sea level pressure, and satellite-observed cloudiness over the western North Pacific (WNP) during August 1991 when the low-level monsoon circulation there became organized as a monsoon gyre. The specific configuration of the monsoon circulation, which herein is called a monsoon gyre, is an episodic event—occurring roughly once per year, for two or three weeks during July, August, or September. As a monsoon gyre, the low-level circulation of the WNP becomes organized as a large cyclonic vortex associated with a nearly circular 2500-km-wide depression in the contours of the sea level pressure. A cyclonically curved band of deep convective clouds rims the southern through eastern periphery of this large vortex. Once this pattern is established, it becomes a prolific generator of mesoscale vortices that emerge from the downstream end of the major peripheral cloud band. These mesoscale vortices form the seed disturbances for midget or small-sized tropical cyclones. The large area encompassed by the outermost closed isobar of the monsoon gyre of August 1991 (the centroid of which moved slowly westward along 20°N) was the site of genesis for two tropical depressions, two tropical storms, and two typhoons during its 20-day westward journey. Initially, small tropical cyclones formed in the peripheral circulation of the gyre and later, the gyre itself evolved into a very large tropical cyclone; this is suggestive of two distinct modes of tropical cyclogenesis: one mode operates to produce small tropical cyclones in the eastern periphery of the gyre, and the other mode operates to accelerate the winds of the monsoon gyre until it becomes a giant tropical cyclone.
Abstract
This paper describes the character and evolution of the low-level wind, sea level pressure, and satellite-observed cloudiness over the western North Pacific (WNP) during August 1991 when the low-level monsoon circulation there became organized as a monsoon gyre. The specific configuration of the monsoon circulation, which herein is called a monsoon gyre, is an episodic event—occurring roughly once per year, for two or three weeks during July, August, or September. As a monsoon gyre, the low-level circulation of the WNP becomes organized as a large cyclonic vortex associated with a nearly circular 2500-km-wide depression in the contours of the sea level pressure. A cyclonically curved band of deep convective clouds rims the southern through eastern periphery of this large vortex. Once this pattern is established, it becomes a prolific generator of mesoscale vortices that emerge from the downstream end of the major peripheral cloud band. These mesoscale vortices form the seed disturbances for midget or small-sized tropical cyclones. The large area encompassed by the outermost closed isobar of the monsoon gyre of August 1991 (the centroid of which moved slowly westward along 20°N) was the site of genesis for two tropical depressions, two tropical storms, and two typhoons during its 20-day westward journey. Initially, small tropical cyclones formed in the peripheral circulation of the gyre and later, the gyre itself evolved into a very large tropical cyclone; this is suggestive of two distinct modes of tropical cyclogenesis: one mode operates to produce small tropical cyclones in the eastern periphery of the gyre, and the other mode operates to accelerate the winds of the monsoon gyre until it becomes a giant tropical cyclone.
Abstract
In its simplest description, the large-scale low-level circulation of summer over the western North Pacific Ocean can be described in terms of low-latitude southwesterlies, a monsoon trough, and a subtropical ridge. When the axis of the monsoon trough is in its normal orientation (NW-SE), tropical cyclones tend to move northwestward on tracks close to those expected from climatology. As an episodic event, the axis of the monsoon trough extends farther north and east than normal and acquires a reverse (SW-NE) orientation. When the monsoon trough becomes reverse oriented, tropical cyclones within it tend to exhibit north-oriented motion and other specific unusual motions such as eastward motion at low latitude and binary interactions with other tropical cyclones along the trough axis. Approximately 80% of the tropical cyclones that are associated with a reverse-oriented monsoon trough move on north-oriented tracks. A tropical cyclone track type, defined herein as the “S”-shaped track, is primarily associated with reverse orientation of the monsoon trough: 23 of 35 cases (66%) of S motion during the period 1978–94 occurred in association with a well-defined reverse-oriented monsoon trough.
Abstract
In its simplest description, the large-scale low-level circulation of summer over the western North Pacific Ocean can be described in terms of low-latitude southwesterlies, a monsoon trough, and a subtropical ridge. When the axis of the monsoon trough is in its normal orientation (NW-SE), tropical cyclones tend to move northwestward on tracks close to those expected from climatology. As an episodic event, the axis of the monsoon trough extends farther north and east than normal and acquires a reverse (SW-NE) orientation. When the monsoon trough becomes reverse oriented, tropical cyclones within it tend to exhibit north-oriented motion and other specific unusual motions such as eastward motion at low latitude and binary interactions with other tropical cyclones along the trough axis. Approximately 80% of the tropical cyclones that are associated with a reverse-oriented monsoon trough move on north-oriented tracks. A tropical cyclone track type, defined herein as the “S”-shaped track, is primarily associated with reverse orientation of the monsoon trough: 23 of 35 cases (66%) of S motion during the period 1978–94 occurred in association with a well-defined reverse-oriented monsoon trough.
Abstract
During 1995, there was a near-record number of named tropical cyclones in the North Atlantic basin. This unusual event fueled speculation that it marked a tangible signal of global climate change, or that it marked a return to a period of higher tropical cyclone activity in the Atlantic, such as that which has been documented to have occurred during the decades of the 1940s through the 1960s. Less publicized, the tropical cyclone activity in other basins during 1995 was almost everywhere below normal. The concept of global and basin “prolific” years and “meager” years is introduced. During the past 30 years, the Atlantic has had two prolific years: 1969 and 1995. Although the annual number of tropical cyclones in each of the other basins is uncorrelated with the annual number of tropical cyclones in the Atlantic, the two Atlantic prolific years of 1969 and 1995 were meager years in some of the other major basins, and below normal years in all of them. In the time series of the annual number of tropical cyclones in all basins except the Atlantic, 1969 and 1995 rank lowest and third lowest, respectively. The known relationships of the annual number of tropical cyclones in the Atlantic with ENSO and with the quasi-biennial ossilation are insufficient to explain the unusual global distribution of tropical cyclones during 1995.
Abstract
During 1995, there was a near-record number of named tropical cyclones in the North Atlantic basin. This unusual event fueled speculation that it marked a tangible signal of global climate change, or that it marked a return to a period of higher tropical cyclone activity in the Atlantic, such as that which has been documented to have occurred during the decades of the 1940s through the 1960s. Less publicized, the tropical cyclone activity in other basins during 1995 was almost everywhere below normal. The concept of global and basin “prolific” years and “meager” years is introduced. During the past 30 years, the Atlantic has had two prolific years: 1969 and 1995. Although the annual number of tropical cyclones in each of the other basins is uncorrelated with the annual number of tropical cyclones in the Atlantic, the two Atlantic prolific years of 1969 and 1995 were meager years in some of the other major basins, and below normal years in all of them. In the time series of the annual number of tropical cyclones in all basins except the Atlantic, 1969 and 1995 rank lowest and third lowest, respectively. The known relationships of the annual number of tropical cyclones in the Atlantic with ENSO and with the quasi-biennial ossilation are insufficient to explain the unusual global distribution of tropical cyclones during 1995.
Abstract
This paper is designed to be an annual summary of the Eastern Hemisphere tropical cyclones of 1995. The tropical cyclone statistics presented are those of the Joint Typhoon Warning Center, Guam. The text focuses primarily upon the tropical cyclones that occurred in the western North Pacific during 1995; however, since the area of responsibility of the Joint Typhoon Warning Center covers the entire Eastern Hemisphere, brief summaries of the tropical cyclone activity within the north Indian Ocean, south Indian Ocean, and the southwest Pacific are also presented. Overall, 1995 was a relatively quiet year in the Eastern Hemisphere: the 22 tropical cyclones of the Southern Hemisphere were only one shy of the record low of 21, and for the first time since 1988 the number of tropical storms and typhoons in the western North Pacific was below normal. In the western North Pacific, there was a marked shift to the west of the preferred region for the genesis and development of tropical cyclones. This is consistent with the end of persistent large-scale circulation anomalies characteristic of the warm phase of the El Niño–Southern Oscillation (ENSO) and the onset (during 1995) of weak ENSO cold-phase anomalies (i.e., La Niña conditions).
Abstract
This paper is designed to be an annual summary of the Eastern Hemisphere tropical cyclones of 1995. The tropical cyclone statistics presented are those of the Joint Typhoon Warning Center, Guam. The text focuses primarily upon the tropical cyclones that occurred in the western North Pacific during 1995; however, since the area of responsibility of the Joint Typhoon Warning Center covers the entire Eastern Hemisphere, brief summaries of the tropical cyclone activity within the north Indian Ocean, south Indian Ocean, and the southwest Pacific are also presented. Overall, 1995 was a relatively quiet year in the Eastern Hemisphere: the 22 tropical cyclones of the Southern Hemisphere were only one shy of the record low of 21, and for the first time since 1988 the number of tropical storms and typhoons in the western North Pacific was below normal. In the western North Pacific, there was a marked shift to the west of the preferred region for the genesis and development of tropical cyclones. This is consistent with the end of persistent large-scale circulation anomalies characteristic of the warm phase of the El Niño–Southern Oscillation (ENSO) and the onset (during 1995) of weak ENSO cold-phase anomalies (i.e., La Niña conditions).
