scholarly journals Recurrent Rossby waves during Southeast Australian heatwaves and links to quasi-resonant amplification and atmospheric blocks

2022 ◽  
Author(s):  
S. Mubashshir Ali ◽  
Matthias Röthlisberger ◽  
Tess Parker ◽  
Kai Kornhuber ◽  
Olivia Martius
Keyword(s):  
Rossby Waves ◽  
Weather Conditions ◽  
The South ◽  
Reanalysis Dataset ◽  
South Pacific Ocean ◽  
Weather Events ◽  
Mean Fields ◽  
High Impact Weather ◽  
Upper Level ◽  
The Relationship

Abstract. In the Northern Hemisphere, recurrence of transient Rossby wave packets over periods of days to weeks, termed RRWPs, may repeatedly create similar weather conditions. This recurrence leads to persistent surface anomalies and high-impact weather events. Here, we demonstrate the significance of RRWPs for persistent heatwaves in the Southern Hemisphere (SH). We investigate the relationship between RRWPs, atmospheric blocking, and amplified quasi-stationary Rossby waves with two cases of heatwaves in Southeast Australia (SEA) in 2004 and 2009. This region has seen extraordinary heatwaves in recent years. We also investigate the importance of transient systems such as RRWPs and two other persistent dynamical drivers: atmospheric blocks and quasi-resonant amplification (QRA). We further explore the link between RRWPs, blocks, and QRA in the SH using the ERA-I reanalysis dataset (1979–2018). We find that QRA and RRWPs are strongly associated: 40 % of QRA days feature RRWPs, and QRA events are 13 times more likely to occur with an RRWPs event than without it. Furthermore, days with QRA and RRWPs show high correlations in the composite mean fields of upper-level flows, indicating that both features have a similar hemispheric flow configuration. Blocking frequencies for QRA and RRWP conditions both increase over the south Pacific Ocean but differ substantially over parts of the south Atlantic and Indian Ocean.

scholarly journals Predictability of prototype flash flood events in the Western Mediterranean under uncertainties of the precursor upper-level disturbance

2006 ◽  
Vol 7 ◽  
pp. 55-63 ◽  
Author(s):  
R. Romero ◽  
A. Martín ◽  
V. Homar ◽  
S. Alonso ◽  
C. Ramis
Keyword(s):  
Case Studies ◽  
Flash Flood ◽  
Western Mediterranean ◽  
Flood Events ◽  
Weather Events ◽  
Systematic Exploration ◽  
High Impact Weather ◽  
Low Levels ◽  
Upper Level ◽  
Level Disturbance

Abstract. The HYDROPTIMET case studies 9-10/06/2000 Catalogne, 8-9/09/2002 Cévennes and 24-26/11/2002 Piémont encompass prototype flash-flood situations in the western Mediterranean, attending to the relevant synoptic and mesoscale signatures identified on the meteorological charts. A prominent mid-tropospheric trough or cut-off low can be identified in all events prior and during the period of heavy rains, which clearly served as the precursor agent for the onset of the flash-flood conditions and the cyclogenesis at low levels. Being aware of the uncertainty in the representation of the upper-level disturbance and the necessity to cope with it within the operational context when attempting to issue short to mid-range numerical weather predictions of these high impact weather events, a systematic exploration of the predictability of the three selected case studies, subject to uncertainties in the representation of the upper-level precursor disturbance, is carried out in this paper by means of numerical simulations.

scholarly journals A database of high-impact weather events in Greece: a descriptive impact analysis for the period 2001–2011

2013 ◽  
Vol 13 (3) ◽  
pp. 727-736 ◽  
Author(s):  
K. Papagiannaki ◽  
K. Lagouvardos ◽  
V. Kotroni
Keyword(s):  
Spatial Distribution ◽  
Impact Analysis ◽  
Heat Waves ◽  
Meteorological Data ◽  
Weather Conditions ◽  
Flash Floods ◽  
High Impact ◽  
Temporal And Spatial Distribution ◽  
Weather Events ◽  
High Impact Weather

Abstract. This paper introduces the development of a database of high-impact weather events that occurred in Greece since 2001. The selected events are related to the occurrence of floods, flash floods, hail, snow/frost, tornados, windstorms, heat waves and lightning with adverse consequences (excluding those related to agriculture). The database includes, among others, the geographical distribution of the recorded events, relevant meteorological data, a brief description of the induced impacts and references in the press. This paper further offers an extensive analysis of the temporal and spatial distribution of high-impact weather events for the period 2001–2011, taking into account the intensity of weather conditions and the consequent impact on the society. Analysis of the monthly distribution of high-impact weather events showed that they are more frequent during October and November. More than 80 people lost their lives, half of which due to flash floods. In what concerns the spatial distribution of high-impact weather events, among the 51 prefectures of the country, Attica, Thessaloniki, Elia and Halkidiki were the most frequently affected areas, mainly by flash floods. Significant was also the share of tornados in Elia, of windstorms in Attica, of lightning and hail events in Halkidiki and of snow/frost events in Thessaloniki.

scholarly journals Large-scale circulation changes over South America are impacting synoptic-scale tropical-extratropical interactions and altering rainfall seasonality

2021 ◽  
Author(s):  
Marcia Zilli ◽  
Neil Hart
Keyword(s):  
Global Warming ◽  
South America ◽  
Rainy Season ◽  
Rossby Waves ◽  
Total Precipitation ◽  
Synoptic Scale ◽  
The South ◽  
Subtropical Jet ◽  
Upper Level ◽  
Extratropical Disturbances

<p>During austral summer, persistent tropical-extratropical (TE) cloud bands, such as the South Atlantic Convergence Zone (SACZ) over South America, link tropical humid areas to the subtropics. Changes in circulation due to global warming is already impacting the location and duration of these TE cloud bands, affecting the hydrological regime of the subtropics. In this study, we present an automatic object-based identification of TE cloud bands which we utilize to obtain an event set of TE cloud bands over South America. This approach and our newly-identified sample base are ideal for understanding interactions between the variability and change in the regional mean state and synoptic-scale weather systems. TE cloud bands are responsible for almost 60% of the subtropical precipitation during the South America rainy season (November to March), mostly produced by SACZ events, a TE cloud band persisting for four or more days. Their location and persistence are modulated by the propagation of synoptic-scale extratropical disturbances interacting with intraseasonal variability in the basic state upper-level zonal wind. The persistent SACZ events (i.e., lasting four or more days) are supported by upper-level westerly anomalies over the subtropics caused by an anomalous trough in the subtropical jet which favours the propagation extratropical disturbances deeper into the tropics. Conversely, transient events occur when the Bolivian High is displaced/expanded southeastward, resulting in upper-level easterly winds occurring over subtropical latitudes and blocking the equatorward propagation of Rossby waves.</p><p>In recent decades, changes in circulation due to global warming has affected the basic-state circulation, resulting in different impacts in transient and persistent TE events throughout the rainy season. Over South America, the number of days with TE events has decreased during the rainy season peak but increased during onset and cessation months, resulting in the displacement of accumulated precipitation into early and late summer. These results are obtained by comparing two periods: 1979-1996 and 1997-2018, excluding ENSO years. These synoptic-scale changes are related to changes in the position of the subtropical jet and its trough, impacting on the propagation of RW towards South America. In the beginning (November) and end (February) of the rainy season, the westerlies have become stronger over subtropical South America, favouring the development of more persistent events and resulting in an increase in the total precipitation during TE events. During the peak of the rainy season (December and January), changes in upper-level circulation have reduced the conditions necessary to the development of TE events, affecting the total precipitation during these months. We show that anomalous subtropical convection from the cloud bands is a source of Rossby waves that interact with the basic flow, resulting in downwind enhancement or damping of the extratropical disturbances. Therefore, these contemporary changes over South America are likely to have implications for changes Rossby Wave spectra in the Southern Hemisphere, especially downstream from the SACZ.</p>

scholarly journals Mesoscale Aspects of the Rapid Intensification of a Tornadic Convective Line across Central Florida: 22–23 February 1998

2007 ◽  
Vol 22 (2) ◽  
pp. 223-243 ◽  
Author(s):  
Alicia C. Wasula ◽  
Lance F. Bosart ◽  
Russell Schneider ◽  
Steven J. Weiss ◽  
Robert H. Johns ◽  
...  
Keyword(s):  
Rapid Development ◽  
Vertical Wind Shear ◽  
Surface Flow ◽  
The South ◽  
Southeast United States ◽  
Central Florida ◽  
Low Level ◽  
Surface Front ◽  
Upper Level ◽  
The Relationship

Abstract The 22–23 February 1998 central Florida tornado outbreak was one of the deadliest and costliest in Florida’s history; a number of long-track tornadoes moved across the Florida peninsula after 0000 UTC 23 February 1998. In the 12–24 h prior to 0000 UTC 23 February, a vigorous upper-level synoptic system was tracking across the southeast United States, and a north–south-oriented convective band located ahead of the cold front was moving eastward across the Gulf of Mexico. Strong vertical wind shear was present in the lowest 1 km, due to a ∼25 m s−1 low-level jet at 925 hPa and south-southeasterly surface flow over the Florida peninsula. Further, CAPE values across the central Florida peninsula exceeded 2500 J kg−1. Upon making landfall on the Florida peninsula, the convective band rapidly intensified and developed into a line of tornadic supercells. This paper examines the relationship between a diabatically induced front across the central Florida peninsula and the rapid development of tornadic supercells in the convective band after 0000 UTC 23 February. Results suggest that persistent strong frontogenesis helped to maintain the front and enhanced ascent in the warm, moist unstable air to the south of the east–west-oriented front on the Florida peninsula, thus allowing the updrafts to rapidly intensify as they made landfall. Further, surface observations from three key locations along the surface front suggest that a mesolow moved eastward along the front just prior to the time when supercells developed. It is hypothesized that the eastward-moving mesolow may have caused the winds in the warm air to the south of the surface front to back to southeasterly and create a favorable low-level wind profile in which supercells could rapidly develop.

Tourism Development in the South Pacific: The Cases of Nauru and Tuvalu

2019 ◽  
Vol 39 (1) ◽  
Author(s):  
Nick Towner ◽  
Semisi Taumoepeau
Keyword(s):  
Swot Analysis ◽  
Tourism Development ◽  
Geographic Location ◽  
South Pacific ◽  
The South ◽  
South Pacific Ocean ◽  
Economic Survival ◽  
Processing Centre ◽  
Remote Island ◽  
The Impact

Abstract Tuvalu and Nauru are isolated developing island nations located in the South Pacific Ocean. In contrast to the established larger Pacific destinations such as Fiji and Tahiti, the tourism industries on both Tuvalu and Nauru are in their infancy. Tourism development in these remote island nations faces a myriad of challenges which include a lack of infrastructure, environmental susceptibility, economic vulnerability, difficulties with access and considerable distances from major tourist markets. This paper reviews tourism on Tuvalu and Nauru and evaluates their current situation regarding potential tourism development through workshops with relevant stakeholders, surveys and subsequent SWOT analysis. The results of the paper outlined a large number of challenges faced by Tuvalu and Nauru due to their geographic location but also highlighted that both Islands possess fascinating and unique features that have the potential to attract niche tourism markets. A key finding of this paper is that the tourism stimulus or potential attraction can also be the chief threat to the islands’ economic survival hence the two edges of the sword. Further research is required to assess the effect of the withdrawal of the Refugee Processing Centre on Nauru’s economy and to evaluate the impact of climate change on Tuvalu’s society and potential adaption strategies.

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