SOME FEATURES OF AN INVERTED V- TYPE EASTERLY WAVE OVER INDIAN SEAS

Abstract. The formation of a river of smoke crossing southern Africa is investigated during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) campaign in September 2017. A complementary set of global and mesoscale numerical simulations as well as ground-based, airborne and space-borne observations of the dynamics, thermodynamics and composition of the atmosphere are used to characterize the river of smoke in terms of timing and vertical extent of the biomass burning aerosol (BBA) layer. The study area was under the synoptic influence of a coastal low rooted in a tropical easterly wave, a high-pressure system over the continent and westerly waves in mid-latitudes, one of which had an embedded cut-off low (CoL). The coastal low interacted with the second of two approaching westerly waves and ultimately formed a mid-level temperate tropical trough (TTT). The TTT created the fast moving air mass transported to the southwestern Indian Ocean as a river of smoke. The CoL, which developed and intensified in the upper levels associated with the first (easternmost) westerly wave, remained stationary above northern Namibia prior to the formation of the TTT and was responsible for the thickening of the BBA layer. This shows that the evolution of the river of smoke is very much tied to the evolution of the TTT while its vertical extent is related to the presence of the CoL. The mechanisms by which the CoL, observed over Namibia in the entrance region of the river of smoke, influences the vertical structure of the BBA layer is mainly associated with the ascending motion above the BBA layer. In the presence of the CoL, the top of the BBA layer over northern Namibia reaches altitudes above 8 km. This is much higher than the average height of the top of the BBA layer over the regions where the smoke comes from (Angola, Zambia, Zimbabwe, Mozambique) which is 5 to 6 km. The results suggest that the interaction between the TTTs and the CoLs which form during the winter may have a role in promoting the transport of BBA from fire-prone regions in the tropical band to the temperate mid-latitudes and southwestern Indian Ocean.

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Intra-seasonal oscfffations of radio refractive index during southwest monsoon over India

MAUSAM ◽

10.54302/mausam.v44i3.3862 ◽

2022 ◽

Vol 44 (3) ◽

pp. 271-276

Author(s):

H. N. SRIVASTAVA ◽

K. C. SINHARAY ◽

R. K. MUKHOPADHYAY

Keyword(s):

Refractive Index ◽

Monsoon Season ◽

Temporal Variations ◽

Southwest Monsoon ◽

The Individual ◽

Southwest Monsoon Season ◽

Seasonal Oscillations ◽

Refractive Index Data ◽

Indian Seas ◽

Variance Explained

The study deals with the spatial and temporal variations of intra-seasonal oscillations in radio refractive index during southwest monsoon season over India and islands over Indian seas. Average daily radio refractive index data from 1 June to 30 September and that of the individual years for the period 1969-1986 were subjected to harmonic analysis to investigate the contributions of various periodicities in monsoon radio refractive index. The inter-annual variability of various intra-seasonal oscillations have been studied for each 5° latitudinal strip from 50 oN to 30° N with the help of variance explained by various frequency modes for different years. Variance explained by 30-60 day and 10-20 day modes were studied in relation to monsoon performance. The northward and eastward propagation of30.60 day mod~ was noticed. The 10.20 day mode and seasonal mode dominate at latitudinal belts 5°N.10oN and 25°N-30°N respectively. Between 10°N and 25°N, both 30-60 day and 10-20 day modes occur.

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Improvement in Track and Intensity Prediction of Indian Seas Tropical Cyclones with Vortex Assimilation

Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change ◽

10.1007/978-94-007-7720-0_18 ◽

2014 ◽

pp. 219-229

Author(s):

Sujata Pattanayak ◽

U. C. Mohanty ◽

S. G. Gopalakrishnan

Keyword(s):

Tropical Cyclones ◽

Intensity Prediction ◽

Indian Seas

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EVENTS IN THE EAST INDIES, 1778–1781. — SUFFREN SAILS FROM BREST FOR INDIA, 1781. — HIS BRILLIANT NAVAL CAMPAIGN IN THE INDIAN SEAS, 1782, 1783

The Influence of Sea Power upon History, 1660–1783 ◽

10.1017/cbo9780511783289.014 ◽

2011 ◽

pp. 419-467

Author(s):

A. T. Mahan

Keyword(s):

East Indies ◽

Indian Seas

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An Analysis of West African Dynamics Using a Linearized GCM*

Journal of the Atmospheric Sciences ◽

10.1175/2007jas2194.1 ◽

2008 ◽

Vol 65 (4) ◽

pp. 1182-1203 ◽

Cited By ~ 19

Author(s):

S. E. Nicholson ◽

A. I. Barcilon ◽

M. Challa

Keyword(s):

Interannual Variability ◽

Spherical Model ◽

Planetary Scale ◽

Wave Disturbances ◽

Easterly Wave ◽

Key Factor ◽

Wave Development ◽

Basic States ◽

Vertical Development ◽

The Waves

Abstract This study utilizes a linear, primitive equation spherical model to study the development and propagation of easterly wave disturbances over West Africa. Perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time. The perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the Sahel and two dry years. The model simulations show consistent contrasts in wave activity between the wet and dry years. The waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere. The waves tend to extend throughout the troposphere to the level of the tropical easterly jet (TEJ) in the wet years, but not in the dry years. The upper-tropospheric shear, which is stronger in wet years, appears to be a key factor in wave development. This shear is dependent on the intensity of the TEJ, suggesting that the TEJ is an important factor in interannual variability in the Sahel. When the overall shear is weak, vertical development is suppressed. Another contrast is that in the dry years the growth rates show a single maximum around 3000–4000 km, but in the wet years there is a second, around 6000–7000 km. This suggests that both synoptic-scale and planetary-scale waves are active in the rainy season of some wet years. Imposing considerations of potential vorticity, the generation of planetary-scale waves implies a strong link between the surface and the TEJ in wet years. Such a link is absent in the dry years. This is likely a major factor in the interannual variability of rainfall in the Sahel.

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Hurricane Juan (2003). Part I: A Diagnostic and Compositing Life Cycle Study

Monthly Weather Review ◽

10.1175/mwr3142.1 ◽

2006 ◽

Vol 134 (7) ◽

pp. 1725-1747 ◽

Cited By ~ 10

Author(s):

Ron McTaggart-Cowan ◽

Eyad H. Atallah ◽

John R. Gyakum ◽

Lance F. Bosart

Keyword(s):

Life Cycle ◽

East Coast ◽

Leading Edge ◽

High Amplitude ◽

Complex Life Cycle ◽

Low Latitude ◽

Initial Development ◽

Easterly Wave ◽

Case Diagnosis

Abstract A detailed analysis of the complex life cycle of Hurricane Juan (in 2003) is undertaken to elucidate the structures and forcings that prevailed over the period leading up to the hurricane’s landfall in Halifax, Nova Scotia, Canada. Despite the presence of easterly wave precursors, Hurricane Juan’s initial development is shown to occur in a baroclinic environment beneath a low-latitude potential vorticity streamer. This feature interacts with a lower-level shear line as the incipient vortex begins to effectively focus ascent and convection. The system undergoes a slow tropical transition over a period of several days as the deep-layer shear over the developing storm decreases. The hurricane is repeatedly perturbed by subsynoptic-scale waves traveling along the leading edge of a large upstream trough. However, Hurricane Juan maintains its tropical structure despite its relatively high formation latitude (28°N) and its northward trajectory. The unusual persistence of the storm’s tropical nature as it propagates northward is of primary interest in this study. In particular, the role of persistent ridging along the east coast of North America is investigated both in high-resolution analyses for Hurricane Juan and in a compositing framework. Dynamic tropopause, quasigeostrophic, and modified Eady model diagnostics are used to elucidate the interactions between Hurricane Juan and this amplified midlatitude flow. Given the strength and persistence of the anomalous ridge–trough couplet both in the case diagnosis and in the composite fields, the study concludes that the presence of prestorm, high-amplitude ridging along the east coast likely reinforced by diabatic ridging downshear of the storm itself produces an environment both dynamically and thermodynamically conducive to the high-latitude landfall of hurricanes still in the tropical phase.

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