scholarly journals Examining Tropical Cyclone–Kelvin Wave Interactions Using Adjoint Diagnostics

2016 ◽  
Vol 144 (11) ◽  
pp. 4421-4439 ◽  
Author(s):  
Carolyn A. Reynolds ◽  
James D. Doyle ◽  
Xiaodong Hong
Keyword(s):  
Tropical Cyclone ◽  
Indian Ocean ◽  
Static Stability ◽  
Kelvin Wave ◽  
Initial State ◽  
Wave Interactions ◽  
Low Level ◽  
Westerly Wind Burst ◽  
The Indian Ocean ◽  
Far Eastern

Abstract The initial-state sensitivity and interactions between a tropical cyclone and atmospheric equatorial Kelvin waves associated with the Madden–Julian oscillation (MJO) during the DYNAMO field campaign are explored using adjoint-based tools from the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). The development of Tropical Cyclone 5 (TC05) coincided with the passage of an equatorial Kelvin wave (KW) and westerly wind burst associated with an MJO that developed in the Indian Ocean in late November 2011. COAMPS 18-h adjoint sensitivities of low-level kinetic energy to changes in initial state winds, temperature, and water vapor are analyzed for both TC05 and the KW to document when the evolution of each system is sensitive to the other. Time series of sensitivity patterns confirm that TC05 and the KW low-level westerlies are sensitive to each other when the KW is to the southwest and south of TC05. While TC05 is not sensitive to the KW after this, the KW low-level westerlies remain sensitive to TC05 until it enters the far eastern Indian Ocean. Vertical profiles of both TC05 and KW sensitivity indicate lower-tropospheric maxima in temperature, wind, and moisture, with KW sensitivity typically 20% smaller than TC05 sensitivity. The magnitude of the sensitivity for both systems is greatest just prior to, and during, their closest proximity. A case study examination reveals that adjoint-based optimal perturbations grow and expand quickly through a dynamic response to decreased static stability. The evolution of moist-only and dry-only initial perturbations illustrates that the moist component is primarily responsible for the initial rapid growth, but that subsequent growth rates are similar.

scholarly journals The Role of Topographically Induced Vortices in Tropical Cyclone Formation over the Indian Ocean

2016 ◽  
Vol 144 (12) ◽  
pp. 4827-4847 ◽  
Author(s):  
Caitlin M. Fine ◽  
Richard H. Johnson ◽  
Paul E. Ciesielski ◽  
Richard K. Taft
Keyword(s):  
Tropical Cyclone ◽  
Indian Ocean ◽  
Madden Julian Oscillation ◽  
Low Level ◽  
Topographic Features ◽  
Westerly Flow ◽  
The Indian Ocean ◽  
Environmental Stratification ◽  
Terrain Features

Abstract The role of Sumatra and adjacent topographic features in tropical cyclone (TC) formation over the Indian Ocean (IO) is investigated. Sumatra, as well as the Malay Peninsula and Java, have mountainous terrain that partially blocks low-level flow under typical environmental stratification. For easterly low-level flow, these terrain features often produce lee vortices, some of which subsequently shed and move westward from the northern and southern tips of Sumatra and thence downstream over the IO. Since Sumatra straddles the equator, extending in a northwest–southeast direction from approximately 6°N to 6°S, the lee vortices, while counter-rotating, are both cyclonic. Hence, they can serve as initial disturbances that eventually contribute to TC formation over the IO. In addition, low-level, equatorial westerly flow impinging on Sumatra is also typically blocked and diverges, at times contributing to cyclonic circulations over the IO, primarily near the southern end of the island. Data from two recent tropical campaigns, the 2008–10 Year of Tropical Convection (YOTC) and the 2011 Dynamics of the Madden–Julian Oscillation (DYNAMO), are used to study these phenomena. These datasets reveal the frequent occurrence of shed and nonshed terrain-induced cyclonic circulations over the IO, the majority of which occur during boreal fall and winter. During the 2.5 yr of the two campaigns, 13 wake vortices (13% of the shed circulations identified) were tracked and observed to subsequently develop into TCs over the northern and southern IO, accounting for 25% of the total TCs forming in the IO during that period.

The Portuguese build an empire.

2021 ◽  
pp. 222-234
Author(s):  
James F. Hancock
Keyword(s):  
Sixteenth Century ◽  
Indian Ocean ◽  
European Countries ◽  
Total Weight ◽  
Open Market ◽  
Fair Game ◽  
The Indian Ocean ◽  
Protection Racket ◽  
Alternative Routes ◽  
Far Eastern

Abstract Albuquerque's victory in Malacca gave Portugal a major foothold in the Far Eastern pepper trade, but the Portuguese were never able to fully dominate it. The chapter summarizes the struggles of Portugal's building of its empire. It also discusses the cartaz system, where the Portuguese claimed suzerainty over the Indian Ocean and no one else was allowed to sail unless they purchased a safe conduct pass. The cartaz obliged Asian ships to call at a Portuguese-controlled port and pay customs duties before proceeding on their voyage. Ships without this document were considered fair game and their goods could be confiscated. It was, pure and simple, a protection racket. The cartaz system, plus customs duties and outright piracy, provided most of the funds defraying the costs of the Portuguese navy and its garrisons. The chapter also outlines the importance of Indian cotton in the Spice Trade and the routes of spices into Europe. Further, the chapter provides highlights of the Portuguese profits on spices. Portuguese imports of pepper held strong over most the sixteenth century. The total weight of the spice cargoes averaged 40,000 to 50,000 quintals (1 quintal = 130 pounds or 59 kilograms) annually in the first half of the century and 60,000 to 70,000 quintals later on. Records have been left of one cargo in 1518 that totalled almost 5 million pounds (2.27 million kilograms), of which 4.7 million pounds (2.13 million kilograms) was pepper, 12,000 pounds (5443 kilograms) cloves, 3000 pounds (1360 kilograms) cinnamon and 2000 pounds (907 kilograms) mace (Krondl, 2007). Most of the pepper and other spices were purchased in Malabar on the open market. Portuguese profits on the pepper trade could run as high as 500%. Lastly, the chapter briefly discusses how other European countries looked for alternative routes to the spices.

Remote influences on the Indian monsoon Low-Level Jet intraseasonal variations

2020 ◽  
Author(s):  
Takeshi Izumo ◽  
Maratt Satheesan Swathi ◽  
Matthieu Lengaigne ◽  
Jérôme Vialard ◽  
Dr Ramesh Kumar
Keyword(s):  
Indian Ocean ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Large Scale ◽  
Indian Monsoon ◽  
Westerly Wind ◽  
Low Level ◽  
Intraseasonal Variations ◽  
The Indian Ocean ◽  
Low Level Jet

<p>A strong Low-Level Jet (LLJ), also known as the Findlater jet, develops over the Arabian Sea during the Indian summer monsoon. This jet is an essential source of moisture for monsoonal rainfall over the densely-populated Indian subcontinent and is a key contributor to the Indian Ocean oceanic productivity by sustaining the western Arabian Sea upwelling systems. The LLJ intensity fluctuates intraseasonally within the ~20- to 90-day band, in relation with the northward-propagating active and break phases of the Indian summer monsoon. Our observational analyses reveal that these large-scale regional convective perturbations  only explain about half of the intraseasonal LLJ variance, the other half being unrelated to large-scale convective perturbations over the Indian Ocean. We show that convective fluctuations in two regions outside the Indian Ocean can remotely force a LLJ intensification, four days later. Enhanced atmosphericdeep convection over the northwestern tropical Pacific yields westerly wind anomalies that propagate westward to the Arabian Sea as baroclinic atmospheric Rossby Waves. Suppressed convection over the eastern Pacific / North American monsoon region yields westerly wind anomalies that propagate eastward to the Indian Ocean as dry baroclinic equatorial Kelvin waves. Those largely independent remote influences jointly explain ~40% of the intraseasonal LLJ variance that is not related to convective perturbations over the Indian Ocean (i.e. ~20% of the total), with the northwestern Pacific contributing twice as much as the eastern Pacific. Taking into account these two remote influences should thus enhance the ability to predict the LLJ.</p><p> </p><p>Related reference: Swathi M.S, Takeshi Izumo, Matthieu Lengaigne, Jérôme Vialard and M.R. Ramesh Kumar:Remote influences on the Indian monsoon Low-Level Jet intraseasonal variations, accepted in Climate Dynamics.</p>

scholarly journals The Impact of Indian Ocean Mean-State Biases in Climate Models on the Representation of the East African Short Rains

2018 ◽  
Vol 31 (16) ◽  
pp. 6611-6631 ◽  
Author(s):  
Linda Hirons ◽  
Andrew Turner
Keyword(s):  
Indian Ocean ◽  
Wind Stress ◽  
Equatorial Indian Ocean ◽  
East African ◽  
Easterly Wind ◽  
Low Level ◽  
The Indian Ocean ◽  
Short Rains ◽  
The Impact ◽  
Mean State

The role of the Indian Ocean dipole (IOD) in controlling interannual variability in the East African short rains, from October to December, is examined in state-of-the-art models and in detail in one particular climate model. In observations, a wet short-rainy season is associated with the positive phase of the IOD and anomalous easterly low-level flow across the equatorial Indian Ocean. A model’s ability to capture the teleconnection to the positive IOD is closely related to its representation of the mean state. During the short-rains season, the observed low-level wind in the equatorial Indian Ocean is westerly. However, half of the models analyzed exhibit mean-state easterlies across the entire basin. Specifically, those models that exhibit mean-state low-level equatorial easterlies in the Indian Ocean, rather than the observed westerlies, are unable to capture the latitudinal structure of moisture advection into East Africa during a positive IOD. Furthermore, the associated anomalous easterly surface wind stress causes upwelling in the eastern Indian Ocean. This upwelling draws up cool subsurface waters, enhancing the zonal sea surface temperature gradient between west and east and strengthening the positive IOD pattern, further amplifying the easterly wind stress. This positive Bjerknes coupled feedback is stronger in easterly mean-state models, resulting in a wetter East African short-rain precipitation bias in those models.

An MJO Simulated by the NICAM at 14- and 7-km Resolutions

2009 ◽  
Vol 137 (10) ◽  
pp. 3254-3268 ◽  
Author(s):  
Ping Liu ◽  
Masaki Satoh ◽  
Bin Wang ◽  
Hironori Fudeyasu ◽  
Tomoe Nasuno ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Atmospheric Model ◽  
Easterly Wind ◽  
Low Level ◽  
Central Indian Ocean ◽  
Simulated Event ◽  
The Indian Ocean ◽  
Substantial Bias ◽  
The Tropics

Abstract This study discloses detailed Madden–Julian oscillation (MJO) characteristics in the two 30-day integrations of the global cloud-system-resolving Nonhydrostatic Icosahedral Atmospheric Model (NICAM) using the all-season real-time multivariate MJO index of Wheeler and Hendon. The model anomaly is derived by excluding the observed climatology because the simulation is sufficiently realistic. Results show that the MJO has a realistic evolution in amplitude pattern, geographical locations, eastward propagation, and baroclinic- and westward-tilted structures. In the central Indian Ocean, convection develops with the low-level easterly wind anomaly then matures where the low-level easterly and westerly anomalies meet. Anomalous moisture tilts slightly with height. In contrast, over the western Pacific, the convection grows with a low-level westerly anomaly. Moisture fluctuations, leading convection in eastward propagation, tilt clearly westward with height. The frictional moisture convergence mechanism operates to maintain the MJO. Such success can be attributed to the explicit representation of the interactions between convection and large-scale circulations. The simulated event, however, grows faster in phases 2 and 3, and peaks with 30% higher amplitude than that observed, although the 7-km version shows slight improvement. The fast-growth phases are induced by the fast-growing low-level convergence in the Indian Ocean and the strongly biased ITCZ in the west Pacific when the model undergoes a spinup. The simulated OLR has a substantial bias in the tropics. Possible solutions to the deficiencies are discussed.

scholarly journals Using Indicators of ENSO, IOD, and SAM to Improve Lead Time and Accuracy of Tropical Cyclone Outlooks for Australia

2020 ◽  
Vol 59 (11) ◽  
pp. 1901-1917
Author(s):  
Andrew D. Magee ◽  
Anthony S. Kiem
Keyword(s):  
Tropical Cyclone ◽  
Indian Ocean ◽  
Lead Time ◽  
Southern Oscillation ◽  
Pearson Correlation ◽  
Southern Annular Mode ◽  
Sea Surface ◽  
Selection Algorithm ◽  
Statistical Framework ◽  
The Indian Ocean

AbstractCatastrophic impacts associated with tropical cyclone (TC) activity mean that the accurate and timely provision of TC outlooks are important to people, places, and numerous sectors in Australia and beyond. In this study, we apply a Poisson regression statistical framework to predict TC counts in the Australian region (AR; 5°–40°S, 90°–160°E) and its four subregions. We test 10 unique covariate models, each using different representations of the influence of El Niño–Southern Oscillation (ENSO), Indian Ocean dipole (IOD), and southern annular mode (SAM) and use an automated covariate selection algorithm to select the optimum combination of predictors. The performance of preseason TC count outlooks generated between April and October for the AR TC season (November–April) and in-season TC count outlooks generated between November and January for the remaining AR TC season are tested. Results demonstrate that skillful TC count outlooks can be generated in April (i.e., 7 months prior to the start of the AR TC season), with Pearson correlation coefficient values between r = 0.59 and 0.78 and covariates explaining between 35% and 60% of the variance in TC counts. The dependence of models on indices representing Indian Ocean sea surface temperature highlights the importance of the Indian Ocean for TC occurrence in this region. Importantly, generating rolling monthly preseason and in-season outlooks for the AR TC season enables the continuous refinement of expected TC counts in a given season.

The port of Al Baleed (southern Oman), the trade in franckincense and its coveted treasures

2020 ◽  
Author(s):  
Alexia Pavan
Keyword(s):  
International Trade ◽  
Indian Ocean ◽  
Bronze Age ◽  
Geographical Location ◽  
Dragon’S Blood ◽  
General Overview ◽  
The Indian Ocean ◽  
Strategic Position ◽  
Far Eastern ◽  
The Bronze Age

Medieval times as Zafar. Placed in a strategic position for its geographical location, climate, availability of water and abundance of fodder, its long history dates back to the Bronze Age. The settlement reached its peak in Mediaeval times when it was a (a hub?) of international trade along the Indian Ocean. Many commodities were exported from the region or passed through the port. Among them a number of regional products such as: myrrh, dragon’s blood, aloe and madder, the most important being, however, frankincense and Arabian horses. Frankincense trade in Mediaeval times is barely studied despite its importance and great incomes generated by this trade during the period. The paper will present a general overview of the site of Al Baleed and its importance in the trade of frankincense, mainly in relation with the Far-eastern market with an overview of the coveted treasures from the region of Dhofar.

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