Dynamics of an Interhemispheric Teleconnection across the Critical Latitude through a Southerly Duct during Boreal Winter*

2015 ◽  
Vol 28 (19) ◽  
pp. 7437-7456 ◽  
Author(s):  
Sen Zhao ◽  
Jianping Li ◽  
Yanjie Li
Keyword(s):  
Indian Ocean ◽  
South Asia ◽  
Southern Africa ◽  
Western Indian Ocean ◽  
Wave Theory ◽  
Stationary Wave ◽  
Boreal Winter ◽  
Stationary Waves ◽  
The North ◽  
Critical Latitude

Abstract In this study, an interhemispheric teleconnection pattern across the critical latitude from southern Africa through South Asia to the North Pacific was revealed in boreal winter monthly averaged 250-hPa streamfunction fields obtained from both the 40-yr ECMWF Re-Analysis (ERA-40) and the NCEP–NCAR reanalysis data from 1957/58 to 2001/02. Classical Rossby wave theory for zonally varying flow in which the effects of the basic-state meridional wind are ignored predicts that stationary Rossby waves cannot propagate across easterlies. To elucidate the underlying mechanisms responsible for this interhemispheric teleconnection, the theoretical basis for stationary wave propagation across the critical latitude is considered, taking into account meridional ambient flow. The theoretical results suggest that the southerly flow over East Africa, the western Indian Ocean, and South Asia creates a path for the northward propagation of stationary waves across the critical latitude. Stationary wavenumber and group velocity analysis, ray tracing, and simple model experiments applied to nearly realistic boreal winter mean flows confirm that disturbances excited in southern Africa and the western Indian Ocean can propagate across the critical latitude to South Asia through the southerly duct and then continue downstream along the North African–Asian subtropical jet.

Interhemispheric Propagation of Stationary Rossby Waves in a Horizontally Nonuniform Background Flow

2015 ◽  
Vol 72 (8) ◽  
pp. 3233-3256 ◽  
Author(s):  
Yanjie Li ◽  
Jianping Li ◽  
Fei Fei Jin ◽  
Sen Zhao
Keyword(s):  
Rossby Wave ◽  
Large Scale ◽  
Critical Role ◽  
Wave Theory ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Stationary Waves ◽  
Asian Monsoon Region ◽  
The North ◽  
Wave Ray

Abstract Significant interhemispheric teleconnections are identified that span the tropical easterlies in the boreal summer 300-hPa streamfunction, such as the North Africa–Antarctic (NAA) and the North Pacific–South America (NPSA) patterns. These patterns are not supported by traditional wave theory, since stationary waves in a basic state without meridional wind would be trapped in the easterlies. To describe the interhemispheric responses more realistically, two-dimensional spherical Rossby wave theory in a horizontally nonuniform basic state is considered. Conditions sufficient for the existence of one propagating wave are obtained, and the meridional group velocity of the wave is shown to have the same direction as the meridional basic wind at the traditional critical latitude. It is concluded that stationary waves with a specific wavelength can propagate across the easterlies from south (north) to north (south) via southerly (northerly) flows. Hence, energy transport by stationary waves on a horizontally nonuniform basic state may produce interhemispheric responses that could pass through the tropical easterly belt. The wave theory and a barotropic model are then applied to idealized and climatological flows. Model results agree well with the theory. In boreal winter and summer, cross-equatorial flows steer stationary waves propagating from one hemisphere to the other across the tropical easterlies, especially over the Australian–Asian monsoon region. It seems that the large-scale monsoonal background flows play a critical role in the interhemispheric teleconnection. Additionally, the wave ray trajectory and model results suggest that the NAA pattern may result from Rossby wave energy dispersion.

scholarly journals Madagascar corals reveal a multidecadal signature of rainfall and river runoff since 1708

2013 ◽  
Vol 9 (2) ◽  
pp. 641-656 ◽  
Author(s):  
C. A. Grove ◽  
J. Zinke ◽  
F. Peeters ◽  
W. Park ◽  
T. Scheufen ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
River Runoff ◽  
Decadal Variability ◽  
Rainfall Variability ◽  
Western Indian Ocean ◽  
Phase Changes ◽  
Monsoon Circulation ◽  
Eastern Australia ◽  
Instrumental Records

Abstract. Pacific Ocean sea surface temperatures (SST) influence rainfall variability on multidecadal and interdecadal timescales in concert with the Pacific Decadal Oscillation (PDO) and Interdecadal Pacific Oscillation (IPO). Rainfall variations in locations such as Australia and North America are therefore linked to phase changes in the PDO. Furthermore, studies have suggested teleconnections exist between the western Indian Ocean and Pacific Decadal Variability (PDV), similar to those observed on interannual timescales related to the El Niño Southern Oscillation (ENSO). However, as instrumental records of rainfall are too short and sparse to confidently assess multidecadal climatic teleconnections, here we present four coral climate archives from Madagascar spanning up to the past 300 yr (1708–2008) to assess such decadal variability. Using spectral luminescence scanning to reconstruct past changes in river runoff, we identify significant multidecadal and interdecadal frequencies in the coral records, which before 1900 are coherent with Asian-based PDO reconstructions. This multidecadal relationship with the Asian-based PDO reconstructions points to an unidentified teleconnection mechanism that affects Madagascar rainfall/runoff, most likely triggered by multidecadal changes in North Pacific SST, influencing the Asian Monsoon circulation. In the 20th century we decouple human deforestation effects from rainfall-induced soil erosion by pairing luminescence with coral geochemistry. Positive PDO phases are associated with increased Indian Ocean temperatures and runoff/rainfall in eastern Madagascar, while precipitation in southern Africa and eastern Australia declines. Consequently, the negative PDO phase that started in 1998 may contribute to reduced rainfall over eastern Madagascar and increased precipitation in southern Africa and eastern Australia. We conclude that multidecadal rainfall variability in Madagascar and the western Indian Ocean needs to be taken into account when considering water resource management under a future warming climate.

Cryptic lineages of little free-tailed bats,Chaerephon pumilus(Chiroptera: Molossidae) from southern Africa and the western Indian Ocean islands

2009 ◽  
Vol 44 (1) ◽  
pp. 55-70
Author(s):  
Peter John Taylor ◽  
Jennifer Lamb ◽  
Devendran Reddy ◽  
Theshnie Naidoo ◽  
Fanja Ratrimomanarivo ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
Western Indian Ocean ◽  
Ocean Islands

Why Does Western Indian Ocean Circulation Connectivity Matter?

2021 ◽  
Author(s):  
Stephen Kelly ◽  
Ekaterina Popova ◽  
Zoe Jacobs
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Western Indian Ocean ◽  
Ocean Model ◽  
Marine Conservation ◽  
Surface Currents ◽  
Resource Exploitation ◽  
Larval Stages ◽  
The North ◽  
Particle Tracking Method

<p>Marine circulation connectivity describes the pathways and timescales over which spatially separated parts of the ocean are connected by oceanic currents. In the Western Indian Ocean (WIO), these pathways and associated timescales are characterised by pronounced seasonal and interannual variability, including monsoon-driven reversal of surface currents in the northern part of the basin.</p><p>Understanding the connectivity timescales in the WIO – and their variability – is important for a multitude of reasons. Ecological connectivity between coral reefs is necessary to maintain their biodiversity, understanding downstream connectivity from marine resource exploitation sites is important to understand which areas are likely to be affected, and circulation connectivity is a key concern when designing marine conservation measures. For example, establishing an effective network of marine protected areas (MPAs) requires that they are connected on ecologically relevant timescales (e.g. the duration of species’ pelagic larval stages), but gaps in the existing MPA network mean that decisions need to be undertaken about which areas to prioritise for future protection. Therefore, knowledge of the advective pathways connecting the WIO over these timescales is essential for effective management of the region.</p><p>Here, a Lagrangian particle tracking method is used in conjunction with a 1/12° resolution ocean model to elucidate the advective pathways mediated by major surface currents in the WIO. Model experiments are performed with virtual particles released into several major WIO currents and tracked for 100 days, and the resulting trajectories are analysed. Significant variability was found, with advective pathways and timescales sensitive to both season and year of release. The main differences are associated with the different monsoon regimes driving changes in connectivity timescales, and reversing direction of advective pathways in the north of the WIO. In addition to this seasonal variability, interannual changes are explored. Case studies of anomalous connectivity pathways / timescales are presented and discussed in the context of extremes in forcing and larger scale variability, including the Indian Ocean Dipole.  </p>

scholarly journals Climatology of the Mascarene High and Its Influence on Weather and Climate over Southern Africa

Climate ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 86 ◽  
Author(s):  
Nkosinathi G. Xulu ◽  
Hector Chikoore ◽  
Mary-Jane M. Bopape ◽  
Nthaduleni S. Nethengwe
Keyword(s):  
Indian Ocean ◽  
Southern Africa ◽  
Lower Troposphere ◽  
Western Indian Ocean ◽  
Vital Role ◽  
Tropical Cyclone Genesis ◽  
Trade Winds ◽  
Mascarene High ◽  
Weather And Climate ◽  
Cyclone Genesis

Globally, subtropical circulation in the lower troposphere is characterized by anticyclones over the oceans. Subtropical anticyclones locate over subtropical belts, modulating weather and climate patterns in those regions. The Mascarene High is an anticyclone located over the Southern Indian Ocean and has a vital role in weather and climate variability over Southern Africa. The warm Western Indian Ocean is a major source of moisture for the subcontinent also permitting tropical cyclone genesis. In this study, we review the dynamics of the Mascarene High, its interactions with the ocean, and its impact on weather and climate over Southern Africa. We also review studies on the evolution of subtropical anticyclones in a future warmer climate. The links between SST modes over the Indian Ocean and the strengthening and weakening of the Mascarene High have been demonstrated. One important aspect is atmospheric blocking due to the Mascarene High, which leads to anomalous rainfall and temperature events over the subcontinent. Blocking leads to landfall of tropical cyclones and slow propagation of cut-off lows resulting in severe weather and flooding over the subcontinent. Understanding how expansion of the Mascarene High due to warming will alter trade winds and storm tracks and change the mean climate of Southern Africa is crucial.

scholarly journals Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part III: Meridional Displacement of Westerly Jet Anomalies during Two Phases of NAO

2007 ◽  
Vol 64 (9) ◽  
pp. 3232-3248 ◽  
Author(s):  
Dehai Luo ◽  
Tingting Gong ◽  
Yina Diao
Keyword(s):  
Theoretical Model ◽  
Storm Track ◽  
Low Frequency ◽  
Stationary Wave ◽  
Negative Phase ◽  
Stationary Waves ◽  
The North ◽  
Westerly Jet ◽  
Two Phases ◽  
The North Atlantic Oscillation

Abstract In this paper, the north–south variability of westerly jet anomalies during the two phases of the North Atlantic Oscillation (NAO) is examined in a theoretical model. It is found that the north–south variability of the zonal mean westerly anomaly results from the interaction between the eddy-driven anomalous stationary waves with a dipole meridional structure (NAO anomalies) and topographically induced climatological stationary waves with a monopole structure, which is dependent upon the phase of the NAO. The westerly jet anomaly tends to shift northward during the positive NAO phase but southward during the negative phase. Synoptic-scale eddies tend to maintain westerly jet anomalies through the excitation of NAO anomalies, but the climatological stationary wave and its position relative to the eddy-driven anomalous stationary wave appear to dominate the north–south shift of westerly jet anomalies. On the other hand, it is shown that when the climatological stationary wave ridge is located downstream of the eddy-driven anomalous stationary wave, the storm track modulated by the NAO pattern splits into two branches for the negative phase, in which the northern branch is generally stronger than the southern one. However, the southern one can be dominant as the relative position between anomalous and climatological stationary waves is within a moderate range. The storm track for the positive phase tends to drift northeastward when there is a phase difference between the NAO anomaly and climatological stationary wave ridge downstream. Thus, it appears that the relationship between the NAO jets and storm tracks can be clearly seen from the present theoretical model.

New genera, species and occurrence records of Goniasteridae (Asteroidea; Echinodermata) from the Indian Ocean

Zootaxa ◽  
2018 ◽  
Vol 4539 (1) ◽  
pp. 1 ◽  
Author(s):  
CHRISTOPHER L. MAH
Keyword(s):  
Indian Ocean ◽  
Deep Sea ◽  
Western Indian Ocean ◽  
Gut Contents ◽  
New Genera ◽  
Late 20Th Century ◽  
The North ◽  
Marine Habitats ◽  
The Indian Ocean ◽  
Occurrence Records

Modern goniasterids are the most numerous of living asteroids in terms of described genera and species and they have important ecological roles from shallow to deep-water marine habitats. Recent MNHN expeditions and historical collections in the USNM have resulted in the discovery of 18 new species, three new genera and multiple new occurrence records from the western Indian Ocean region including Madagascar, Glorioso and Mayotte islands, Walters Shoal, South Africa, and Somalia. This report provides the first significant contribution to knowledge of deep-sea Asteroidea from the Indian Ocean since the late 20th Century. Several deep-sea species, previously known from the North Pacific are now reported from the western Indian Ocean. Gut contents from Stellaster and Ogmaster indicate deposit feeding. Feeding modes of this and other deep-sea species are discussed. Comments are made on fossil members of included taxa. A checklist of Indian Ocean Goniasteridae is also included.

First occurrence of the moray eel Gymnothorax prolatus Sasaki & Amaoka, 1991 (Teleostei: Anguilliformes: Muraenidae) from the northern Indian Ocean

2015 ◽  
Vol 8 ◽  
Author(s):  
Anil Mohapatra ◽  
Dipanjan Ray ◽  
David G. Smith
Keyword(s):  
Indian Ocean ◽  
Arabian Sea ◽  
Western Indian Ocean ◽  
Northern Indian Ocean ◽  
The North ◽  
First Occurrence ◽  
The Indian Ocean ◽  
First Time ◽  
North Western ◽  
Moray Eel

Gymnothorax prolatusis recorded for the first time from the Indian Ocean on the basis of four specimens collected in the Bay of Bengal off India and one from the Arabian Sea off Pakistan. These records extend the range of the species from Taiwan to the north-western Indian Ocean.

scholarly journals Central-West Argentina Summer Precipitation Variability and Atmospheric Teleconnections

2012 ◽  
Vol 25 (5) ◽  
pp. 1657-1677 ◽  
Author(s):  
Eduardo A. Agosta ◽  
Rosa H. Compagnucci
Keyword(s):  
Indian Ocean ◽  
Southern Oscillation ◽  
Vertical Motion ◽  
Summer Precipitation ◽  
Western Indian Ocean ◽  
Stationary Wave ◽  
Precipitation Variability ◽  
South Atlantic ◽  
Spectral Variation ◽  
The South

The interannual-to-multidecadal variability of central-west Argentina (CWA) summer (October–March) precipitation and associated tropospheric circulation are studied in the period 1900–2010. Precipitation shows significant quasi cycles with periods of about 2, 4–5, 6–8, and 16–22 yr. The quasi-bidecadal oscillation is significant from the early 1910s until the mid-1970s and is present in pressure time series over the southwestern South Atlantic. According to the lower-frequency spectral variation, a prolonged wet spell is observed from 1973 to the early 2000s. The precipitation variability shows a reversal trend since then. In that wet epoch, the regionally averaged precipitation has been increased about 24%. The lower-frequency spectral variation is attributed to the climate shift of 1976/77. From the early twentieth century until the mid-1970s, the precipitation variability is associated with barotropic quasi-stationary wave (QSW) propagation from the tropical southern Indian Ocean and the South Pacific, generating vertical motion and moisture anomalies at middle-to-subtropical latitudes east of the Andes over southern South America. The QSW propagation could be related to anomalous convection partly induced by tropical anomalous SSTs in the western Indian Ocean (WIO). It could also be linked to another midlatitude source along the storm tracks, to the east of New Zealand. After 1976/77, the precipitation variability is associated with equatorial symmetric circulation anomalies linked to El Niño–Southern Oscillation (ENSO)-like warmer conditions. Positive moisture anomalies are consistently observed at lower latitudes in association with inflation of the western flank of the South Atlantic anticyclone. Outside of this, the precipitation variability is unrelated to ENSO.

scholarly journals QUASI-STATIONARY PLANETARY WAVES IN MID-LATITUDE STRATOSPHERE–MESOSPHERE IN WINTER 2011-2020

2021 ◽  
pp. 307-311
Author(s):  
Chenning Zhang ◽  
Oleksandr Evtushevsky ◽  
Gennadi Milinevsky
Keyword(s):  
Surface Pressure ◽  
Satellite Data ◽  
Geopotential Height ◽  
Stationary Wave ◽  
Planetary Waves ◽  
Stationary Waves ◽  
Aleutian Low ◽  
The North ◽  
Pressure Anomaly ◽  
Icelandic Low

The 10-year climatology (2011–2020) of quasi-stationary planetary waves in the mid-latitude stratosphere and mesosphere (40–50N, up to 90 km) has been analyzed. Longitude–altitude sections of geopotential height and ozone have been obtained using the Aura MLS satellite data. It is found that stationary wave 1 propagates into the mesosphere from the North American High and Icelandic Low, which are adjacent surface pressure anomalies in the structure of stationary wave 2. Unexpectedly, the strongest pressure anomaly in the Aleutian Low region does not contribute to the stationary wave 1 formation in the mesosphere. The vertical phase transformations of stationary waves in geopotential height and ozone show inconsistencies that should be studied separately.

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