Global Perspective of the Quasi-Biweekly Oscillation*

2009 ◽  
Vol 22 (6) ◽  
pp. 1340-1359 ◽  
Author(s):  
Kazuyoshi Kikuchi ◽  
Bin Wang
Keyword(s):  
Central America ◽  
Rossby Wave ◽  
Austral Summer ◽  
Global Perspective ◽  
Asia Pacific ◽  
Boreal Summer ◽  
Mean Flow ◽  
Wave Trains ◽  
Mean Climate ◽  
Long Term Observation

Abstract The quasi-biweekly oscillation (QBW: here defined as a 12–20-day oscillation) is one of the major systems that affect tropical and subtropical weather and seasonal mean climate. However, knowledge is limited concerning its temporal and spatial structures and dynamics, particularly in a global perspective. To advance understanding of the QBW, its life cycle is documented using a tracking method and extended EOF analysis. Both methods yield consistent results. The analyses reveal a wide variety of QBW activity in terms of initiation, movement, development, and dissipation. The convective anomalies associated with the QBW are predominant in the latitude bands between 10° and 30° in both hemispheres. The QBW modes tend to occur regionally and be associated with monsoons. Three boreal summer modes are identified in the Asia–Pacific, Central America, and subtropical South Pacific regions. Five austral summer modes are identified in the Australia–southwest Pacific, South Africa–Indian Ocean, South America–Atlantic, subtropical North Pacific, and North Atlantic–North Africa regions. The QBW modes are classified into two categories: westward- and eastward-propagating modes. The westward mode is found in the Asia–Pacific and Central America regions during boreal summer; it originates in the tropics and dissipates in the subtropics. The behavior of the westward-propagating mode can be understood in terms of equatorial Rossby waves in the presence of monsoon mean flow and convective coupling. The eastward-propagating mode, on the other hand, connects with upstream extratropical Rossby wave trains and propagates primarily eastward and equatorward. Barotropic Rossby wave trains play an essential role in controlling initiation, development, and propagation of the eastward QBW mode in the subtropics. The results therefore suggest that not only tropical but also extratropical dynamics are required for fully understanding the behavior of the QBW systems worldwide. The new conceptual picture of QBW obtained here based on long-term observation provides valuable information on the behavior of QBW systems in a global perspective, which is important for a thorough understanding of tropical variability on a time scale between day-to-day weather and the Madden–Julian oscillation.

scholarly journals On the Drivers of Temperature Extremes on the Antarctic Peninsula During Austral Summer

2021 ◽  
Author(s):  
Sai Wang ◽  
Minghu Ding ◽  
Ge Liu ◽  
Ting Wei ◽  
Wenqian Zhang ◽  
...  
Keyword(s):  
Air Temperature ◽  
Antarctic Peninsula ◽  
Rossby Wave ◽  
Austral Summer ◽  
Polar Front ◽  
Temperature Extremes ◽  
Cold Events ◽  
Wave Trains ◽  
The Antarctic ◽  
Polar Front Jet

Abstract On the basis of surface air temperature (SAT) observations from the Great Wall Station located on the Antarctic Peninsula (AP) and ERA-Interim reanalysis data, the present manuscript investigates the role of atmospheric flow at intraseasonal and synoptic time scales in driving the temperature extremes over the AP during austral summer. Both warm and cold events can persist for multiple days and were maintained mainly by the advection of seasonal air temperature by intraseasonal winds. Synoptic winds can influence the temperature change around the peak time through their advection of seasonal temperature, thus determining the time of peak temperature anomalies. The generation of intraseasonal winds was closely associated with Rossby wave trains propagating along the polar front jet over the Atlantic sector of the Southern Ocean before the warm and cold events. The synoptic height anomalies before the warm events were also manifested as Rossby wave trains propagating along the polar front jet. However, synoptic Rossby wave trains were almost absent when the cold events occurred. Further analysis indicates that the weakened background flow during the cold events may have hindered the eastward travel of synoptic eddies. This study provides an important guidance for subseasonal to seasonal prediction on the AP.

Utility of Hovmöller diagrams to diagnose Rossby wave trains

2011 ◽  
Author(s):  
Ilona Glatt ◽  
Andreas Dörnbrack ◽  
Sarah Jones ◽  
Julia Keller ◽  
O. Martius ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Wave Trains

scholarly journals Bay of Bengal‐East Asia‐Pacific Teleconnection in Boreal Summer

2019 ◽  
Vol 124 (8) ◽  
pp. 4395-4412 ◽  
Author(s):  
Ruowen Yang ◽  
Shu Gui ◽  
Jie Cao
Keyword(s):  
East Asia ◽  
Bay Of Bengal ◽  
Asia Pacific ◽  
Boreal Summer

scholarly journals Tropical Cyclogenesis in the Western North Pacific as Revealed by the 2008–09 YOTC Data*

2013 ◽  
Vol 28 (4) ◽  
pp. 1038-1056 ◽  
Author(s):  
Yamei Xu ◽  
Tim Li ◽  
Melinda Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Energy Dispersion ◽  
Reanalysis Dataset ◽  
Initial Development ◽  
Wave Trains

Abstract The Year of Tropical Convection (YOTC) high-resolution global reanalysis dataset was analyzed to reveal precursor synoptic-scale disturbances related to tropical cyclone (TC) genesis in the western North Pacific (WNP) during the 2008–09 typhoon seasons. A time filtering is applied to the data to isolate synoptic (3–10 day), quasi-biweekly (10–20 day), and intraseasonal (20–90 day) time-scale components. The results show that four types of precursor synoptic disturbances associated with TC genesis can be identified in the YOTC data. They are 1) Rossby wave trains associated with preexisting TC energy dispersion (TCED) (24%), 2) synoptic wave trains (SWTs) unrelated to TCED (32%), 3) easterly waves (EWs) (16%), and 4) a combination of either TCED-EW or SWT-EW (24%). The percentage of identifiable genesis events is higher than has been found in previous analyses. Most of the genesis events occurred when atmospheric quasi-biweekly and intraseasonal oscillations are in an active phase, suggesting a large-scale control of low-frequency oscillations on TC formation in the WNP. For genesis events associated with SWT and EW, maximum vorticity was confined in the lower troposphere. During the formation of Jangmi (2008), maximum Rossby wave energy dispersion appeared in the middle troposphere. This differs from other TCED cases in which energy dispersion is strongest at low level. As a result, the midlevel vortex from Rossby wave energy dispersion grew faster during the initial development stage of Jangmi.

scholarly journals Global carbonyl sulfide (OCS) measured by MIPAS/Envisat during 2002–2012

2016 ◽  
Author(s):  
Norbert Glatthor ◽  
Michael Höpfner ◽  
Adrian Leyser ◽  
Gabriele P. Stiller ◽  
Thomas von Clarmann ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Michelson Interferometer ◽  
Austral Summer ◽  
Emission Spectra ◽  
Set Covering ◽  
Boreal Summer ◽  
Systematic Bias ◽  
High Latitudes ◽  
Data Set ◽  
The Tropics

Abstract. We present a global OCS data set covering the period June 2002 to April 2012, derived from FTIR limb emission spectra measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the ENVISAT satellite. The vertical resolution is 4–5 km in the height region 6–15 km and 15 km at 40 km altitude. The total estimated error amounts to 40–50 pptv between 10 and 20 km and to 120 pptv at 40 km altitude. MIPAS OCS data show no systematic bias with respect to balloon observations, with deviations mostly below ±50 pptv. However, they are systematically higher than the OCS volume mixing ratios of the ACE-FTS instrument on SCISAT, with maximum deviations of up to 100 pptv in the altitude region 13–16 km. The data set of MIPAS OCS exhibits only moderate interannual variations and low interhemispheric differences. Average concentrations at 10 km altitude range from 480 pptv at high latitudes to 500–510 pptv in the tropics and at northern mid-latitudes. Seasonal variations at 10 km altitude amount up to 35 pptv in the northern and up to 15 pptv in the southern hemisphere. Northern hemispheric OCS abundances at 10 km altitude peak in June in the tropics and around October at high latitudes, while the respective southern hemispheric maxima were observed in July and in November. Global OCS distributions at 250 hPa (~ 10–11 km) show enhanced values at low latitudes, peaking during boreal summer above the western Pacific and the Indian Ocean, which indicates oceanic release. Further, a region of depleted OCS amounts extending from Brazil to central and southern Africa was detected at this altitude, which is most pronounced in austral summer. This depletion is related to seasonally varying vegetative uptake by the tropical forests. Typical signatures of biomass burning like the southern hemispheric biomass burning plume are not visible in MIPAS data, indicating that this process is only a minor source of tropospheric OCS. At the 150 hPa level (~ 13–14 km) enhanced amounts of OCS were also observed inside the Asian Monsoon Anticyclone, but this enhancement is not especially outstanding as compared to other low latitude regions at the same altitude. At the 80 hPa level (~ 17–18 km) equatorward transport of mid-latitude air masses containing lower OCS amounts around the summertime anticyclones was observed. A significant trend could not be detected in tropospheric MIPAS OCS amounts, which points to globally balanced sources and sinks.

Digital Libraries Overview and Globalization

2009 ◽  
pp. 562-573
Author(s):  
Soh Whee Kheng Grace
Keyword(s):  
Digital Library ◽  
Digital Libraries ◽  
Global Perspective ◽  
First Century ◽  
Asia Pacific ◽  
Pacific Region ◽  
The World ◽  
Library Development ◽  
National Libraries ◽  
Collaborative Efforts

Library digitization on a global basis is essential in the twenty-first century. The digital library development initiatives in most countries depend substantially on their national libraries. This chapter focuses on an overview of how national libraries of 14 countries in the Asia-Pacific region are involved in digital library initiatives. Most libraries participate in the collaborative efforts to build digital libraries with support from their government. Some focus on digitization and preservation activities, while others concentrate on digitization standards. Requirements for digital library implementation from a global perspective are essential. With the understanding of the current situation in Asia Pacific, we can understand the readiness of national libraries aiming for globalization in this part of the world, and action can be taken to achieve the aim. The globalization of digital libraries is what the world should be heading towards as we enter the next century.

scholarly journals The Structure of Baroclinic Modes in the Presence of Baroclinic Mean Flow

2020 ◽  
Vol 50 (1) ◽  
pp. 239-253
Author(s):  
K. H. Brink ◽  
J. Pedlosky
Keyword(s):  
Rossby Wave ◽  
Potential Vorticity ◽  
Vertical Structure ◽  
Horizontal Gradient ◽  
Mean Flow ◽  
Stable Mode ◽  
Oceanic Current ◽  
Unstable Solutions ◽  
Rossby Wave Propagation ◽  
Baroclinic Modes

AbstractThis contribution seeks to understand the vertical structure of linearized quasigeostrophic baroclinic modes when they are modified by the presence of a baroclinic mean flow and associated potential vorticity gradients. It is found that even modest, O(0.05 m s−1), mean flows can give rise to very substantial changes in modal structures, often in the sense of increased surface intensification. The extent to which stable modes are modified depends strongly on the direction of Rossby wave propagation. Further, baroclinically unstable solutions can appear, and a meaningful inviscid critical-layer solution can occur at the transition to instability when the horizontal gradient of potential vorticity changes sign at some depth within the water column. In addition, the gravest, n = 0, vertical stable mode is no longer strictly barotropic, but rather it can carry density variability at frequencies much higher than those possible for baroclinic (higher) Rossby wave modes. This finding appears to be consistent with oceanic current-meter observations that suggest temperature variability propagation even when the frequency is too high for traditional baroclinic Rossby waves to exist.

scholarly journals Relation Between the Interannual Variability in the Stratospheric Rossby Wave Forcing and Zonal Mean Fields Suggesting an Interhemispheric Link in the Stratosphere

2019 ◽  
Author(s):  
Yuki Matsushita ◽  
Daiki Kado ◽  
Masashi Kohma ◽  
Kaoru Sato
Keyword(s):  
Interannual Variability ◽  
Rossby Wave ◽  
Reanalysis Data ◽  
Mean Flow ◽  
Flux Divergence ◽  
Wave Forcing ◽  
Mean Fields ◽  
Meridional Cross Section ◽  
The Cross ◽  
Modern Era

Abstract. Focusing on the interannual variabilities in the zonal mean fields and Rossby wave forcing in austral winter, an interhemispheric coupling in the stratosphere is examined using reanalysis data: the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). In the present study, the Eliassen-Palm (EP) flux divergence averaged over the latitude and height regions of 50°–30° S and 0.3–1 hPa, respectively, are used as a proxy of the Rossby wave forcing, where the absolute value of the EP flux divergence is maximized in the winter in the Southern Hemisphere (SH). The interannual variabilities in the zonal mean temperature and zonal wind are significantly correlated with the SH Rossby wave forcing in the stratosphere in both the SH and Northern Hemisphere (NH). The interannual variability in the strength of the poleward residual mean flow in the SH stratosphere is also correlated with the strength of the wave forcing. This correlation is significant even around the equator at an altitude of 40 km and at NH low latitudes of 20–40 km. The temperature anomaly is consistent with this residual mean flow anomaly. The relationship between the cross-equatorial flow and the zonal mean absolute angular momentum gradient (My) is examined in the meridional cross section. The My around the equator at the altitude of 40 km is small when the wave forcing is strong, which provides a pathway for the cross-equatorial residual mean flow. These results indicate that an interhemispheric coupling is present in the stratosphere through the meridional circulation modulated by the Rossby wave forcing.

Sign in / Sign up

Export Citation Format

Share Document