scholarly journals A Physically Based Climatology of the Occurrence and Intensification of Australian East Coast Lows

2019 ◽  
Vol 32 (10) ◽  
pp. 2823-2841 ◽  
Author(s):  
Leone Cavicchia ◽  
Acacia Pepler ◽  
Andrew Dowdy ◽  
Kevin Walsh
Keyword(s):  
East Coast ◽  
Thermal Structure ◽  
Dominant Role ◽  
Formation Mechanisms ◽  
Limited Area ◽  
Rapid Intensification ◽  
Physically Based ◽  
The Tropics ◽  
Coastal Damage ◽  
Underlying Processes

Abstract The subtropical part of the eastern Australian seaboard experiences intense cyclonic activity. The severe damage caused by the intense storms in the region, known as east coast lows (ECLs), has motivated a number of recent studies. Cyclones in this region appear to be driven by a combination of different (barotropic and baroclinic) formation mechanisms, consistent with the view emerging in the last decades that cyclones span a continuous spectrum of dynamical structures, with the barotropically driven tropical cyclone and the baroclinically driven extratropical cyclone being only the extremes of such a spectrum. In this work we revisit the climatology of cyclone occurrence in the subtropical east coast of Australia as seen in a global reanalysis, systematically applying classification criteria based on the cyclone vertical structure and thermal core. Moreover, we investigate the underlying processes driving the cyclone rapid intensification by means of an atmospheric limited-area energetics analysis. We show that ECLs have different spatial patterns according to the cyclone thermal structure, with the fraction of hybrid cyclones being larger toward the tropics and closer to the coast. Moreover, we find that explosively deepening cyclones in this region are driven by a different combination of processes with respect to the global case, with barotropic processes in the surrounding environment having a more dominant role in the energetics of cyclone rapid intensification. The findings of this work contribute to understanding the physical processes underlying the formation and intensification of Australian east coast lows and the associated coastal damage and risk.

scholarly journals Energetics and Dynamics of Subtropical Australian East Coast Cyclones: Two Contrasting Cases

2018 ◽  
Vol 146 (5) ◽  
pp. 1511-1525 ◽  
Author(s):  
Leone Cavicchia ◽  
Andrew Dowdy ◽  
Kevin Walsh
Keyword(s):  
Phase Space ◽  
East Coast ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Limited Area ◽  
Physically Based ◽  
Occurrence Times ◽  
Broad Classification ◽  
Coast Region

Abstract The subtropical east coast region of Australia is characterized by the frequent occurrence of low pressure systems, known as east coast lows (ECLs). The more intense ECLs can cause severe damage and disruptions to this region. While the term “east coast low” refers to a broad classification of events, it has been argued that different ECLs can have substantial differences in their nature, being dominated by baroclinic and barotropic processes in different degrees. Here we reexamine two well-known historical ECL case studies under this perspective: the Duck storm of March 2001 and the Pasha Bulker storm of June 2007. Exploiting the cyclone phase space analysis to study the storms’ full three-dimensional structure, we show that one storm has features similar to a typical extratropical frontal cyclone, while the other has hybrid tropical–extratropical characteristics. Furthermore, we examine the energetics of the atmosphere in a limited area including both systems for the ECL occurrence times, and show that the two cyclones are associated with different signatures in the energy conversion terms. We argue that the systematic use of the phase space and energetics diagnostics can form the basis for a physically based classification of ECLs, which is important to advance the understanding of ECL risk in a changing climate.

scholarly journals NASA’s Hurricane and Severe Storm Sentinel (HS3) Investigation

2016 ◽  
Vol 97 (11) ◽  
pp. 2085-2102 ◽  
Author(s):  
Scott A. Braun ◽  
Paul A. Newman ◽  
Gerald M. Heymsfield
Keyword(s):  
East Coast ◽  
Inner Core ◽  
The United States ◽  
Intensity Change ◽  
Western Coast ◽  
Rapid Intensification ◽  
Physical Processes ◽  
Severe Storm ◽  
Saharan Air Layer ◽  
Global Hawk

Abstract The National Aeronautics and Space Administration’s (NASA) Hurricane and Severe Storm Sentinel (HS3) investigation was a multiyear field campaign designed to improve understanding of the physical processes that control hurricane formation and intensity change, specifically the relative roles of environmental and inner-core processes. Funded as part of NASA’s Earth Venture program, HS3 conducted 5-week campaigns during the hurricane seasons of 2012–14 using the NASA Global Hawk aircraft, along with a second Global Hawk in 2013 and a WB-57f aircraft in 2014. Flying from a base at Wallops Island, Virginia, the Global Hawk could be on station over storms for up to 18 h off the East Coast of the United States and up to about 6 h off the western coast of Africa. Over the 3 years, HS3 flew 21 missions over nine named storms, along with flights over two nondeveloping systems and several Saharan air layer (SAL) outbreaks. This article summarizes the HS3 experiment, the missions flown, and some preliminary findings related to the rapid intensification and outflow structure of Hurricane Edouard (2014) and the interaction of Hurricane Nadine (2012) with the SAL.

scholarly journals The distribution of sea-salt aerosol in the global troposphere

2019 ◽  
Vol 19 (6) ◽  
pp. 4093-4104 ◽  
Author(s):  
Daniel M. Murphy ◽  
Karl D. Froyd ◽  
Huisheng Bian ◽  
Charles A. Brock ◽  
Jack E. Dibb ◽  
...  
Keyword(s):  
Dominant Role ◽  
Open Water ◽  
Sea Salt ◽  
Transport Models ◽  
Upper Troposphere ◽  
Sea Salt Aerosol ◽  
Pack Ice ◽  
Wide Range ◽  
Wet Scavenging ◽  
The Tropics

Abstract. We present the first data on the concentration of sea-salt aerosol throughout most of the depth of the troposphere and over a wide range of latitudes, which were obtained during the Atmospheric Tomography (ATom) mission. Sea-salt concentrations in the upper troposphere are very small, usually less than 10 ng per standard m3 (about 10 parts per trillion by mass) and often less than 1 ng m−3. This puts stringent limits on the contribution of sea-salt aerosol to halogen and nitric acid chemistry in the upper troposphere. Within broad regions the concentration of sea-salt aerosol is roughly proportional to water vapor, supporting a dominant role for wet scavenging in removing sea-salt aerosol from the atmosphere. Concentrations of sea-salt aerosol in the winter upper troposphere are not as low as in the summer and the tropics. This is mostly a consequence of less wet scavenging in the drier, colder winter atmosphere. There is also a source of sea-salt aerosol over pack ice that is distinct from that over open water. With a well-studied and widely distributed source, sea-salt aerosol provides an excellent test of wet scavenging and vertical transport of aerosols in chemical transport models.

scholarly journals Estimating the Ice Crystal Enhancement Factor in the Tropics

2011 ◽  
Vol 68 (7) ◽  
pp. 1424-1434 ◽  
Author(s):  
Xiping Zeng ◽  
Wei-Kuo Tao ◽  
Toshihisa Matsui ◽  
Shaocheng Xie ◽  
Stephen Lang ◽  
...  
Keyword(s):  
Ice Crystal ◽  
Middle Latitudes ◽  
Ice Nuclei ◽  
Significant Difference ◽  
Physically Based ◽  
Cloud Resolving Model ◽  
The Difference ◽  
The Tropics ◽  
Cloud Condition

Abstract The ice crystal enhancement (IE) factor, defined as the ratio of the ice crystal to ice nuclei (IN) number concentrations for any particular cloud condition, is needed to quantify the contribution of changes in IN to global warming. However, the ensemble characteristics of IE are still unclear. In this paper, a representation of the IE factor is incorporated into a three-ice-category microphysical scheme for use in long-term cloud-resolving model (CRM) simulations. Model results are compared with remote sensing observations, which suggest that, absent a physically based consideration of how IE comes about, the IE factor in tropical clouds is about 103 times larger than that in midlatitudinal ones. This significant difference in IE between the tropics and middle latitudes is consistent with the observation of stronger entrainment and detrainment in the tropics. In addition, the difference also suggests that cloud microphysical parameterizations depend on spatial resolution (or subgrid turbulence parameterizations within CRMs).

Simuliidae of the Buganda, Eastern and Western Provinces of Uganda

1937 ◽  
Vol 28 (2) ◽  
pp. 289-309 ◽  
Author(s):  
E. G. Gibbins
Keyword(s):  
Southern Hemisphere ◽  
East Coast ◽  
Northern Province ◽  
African Continent ◽  
River Nile ◽  
High Mountains ◽  
The West ◽  
Number Of Species ◽  
The Tropics

Five years ago, when a study was commenced of the Simuliid fauna of Uganda, 24 species were known from the whole of Africa. To-day, Uganda can claim more than that number within its own boundaries. In fact 30 species are known to occur in the country. And yet it is probable that many more species remain to be discovered, particularly as the investigation has not included the Northern Province, which will undoubtedly prove to be one of the richest in Simulium, since within its confines are the River Nile and its many subsidiary tributaries. Quite a number of species found in Uganda occur in other parts of the African continent. Some extend their distribution over to the west and also to the east coast, while other species do not confine their range to the tropics and are found as far afield as the Transvaal and Natal in the Southern Hemisphere. Early observations (1934) indicated a specialised Simuliid fauna on each of the high mountains in Uganda, and while this may still be true in the case of some species, subsequent investigations have shown that several have a wider distribution.

scholarly journals Primary and secondary aerosols in Beijing in winter: sources, variations and processes

2016 ◽  
Vol 16 (13) ◽  
pp. 8309-8329 ◽  
Author(s):  
Yele Sun ◽  
Wei Du ◽  
Pingqing Fu ◽  
Qingqing Wang ◽  
Jie Li ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Biomass Burning ◽  
Coal Combustion ◽  
Dominant Role ◽  
Liquid Water Content ◽  
Oxidation States ◽  
Gas Chromatography Mass Spectrometry ◽  
Formation Mechanisms ◽  
Aerosol Composition ◽  
Secondary Aerosols

Abstract. Winter has the worst air pollution of the year in the megacity of Beijing. Despite extensive winter studies in recent years, our knowledge of the sources, formation mechanisms and evolution of aerosol particles is not complete. Here we have a comprehensive characterization of the sources, variations and processes of submicron aerosols that were measured by an Aerodyne high-resolution aerosol mass spectrometer from 17 December 2013 to 17 January 2014 along with offline filter analysis by gas chromatography/mass spectrometry. Our results suggest that submicron aerosols composition was generally similar across the winter of different years and was mainly composed of organics (60 %), sulfate (15 %) and nitrate (11 %). Positive matrix factorization of high- and unit-mass resolution spectra identified four primary organic aerosol (POA) factors from traffic, cooking, biomass burning (BBOA) and coal combustion (CCOA) emissions as well as two secondary OA (SOA) factors. POA dominated OA, on average accounting for 56 %, with CCOA being the largest contributor (20 %). Both CCOA and BBOA showed distinct polycyclic aromatic hydrocarbons (PAHs) spectral signatures, indicating that PAHs in winter were mainly from coal combustion (66 %) and biomass burning emissions (18 %). BBOA was highly correlated with levoglucosan, a tracer compound for biomass burning (r2 = 0.93), and made a considerable contribution to OA in winter (9 %). An aqueous-phase-processed SOA (aq-OOA) that was strongly correlated with particle liquid water content, sulfate and S-containing ions (e.g. CH2SO2+) was identified. On average aq-OOA contributed 12 % to the total OA and played a dominant role in increasing oxidation degrees of OA at high RH levels (> 50 %). Our results illustrate that aqueous-phase processing can enhance SOA production and oxidation states of OA as well in winter. Further episode analyses highlighted the significant impacts of meteorological parameters on aerosol composition, size distributions, oxidation states of OA and evolutionary processes of secondary aerosols.

scholarly journals The Effect of the Ocean Eddy on Tropical Cyclone Intensity

2007 ◽  
Vol 64 (10) ◽  
pp. 3562-3578 ◽  
Author(s):  
Chun-Chieh Wu ◽  
Chia-Ying Lee ◽  
I-I. Lin
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Mixed Layer ◽  
Thermal Structure ◽  
Critical Role ◽  
Strong Mixing ◽  
Rapid Intensification ◽  
Tropical Cyclone Intensity ◽  
Cyclone Intensity ◽  
The Impact

Abstract The rapid intensification of Hurricane Katrina followed by the devastation of the U.S. Gulf States highlights the critical role played by an upper-oceanic thermal structure (such as the ocean eddy or Loop Current) in affecting the development of tropical cyclones. In this paper, the impact of the ocean eddy on tropical cyclone intensity is investigated using a simple hurricane–ocean coupled model. Numerical experiments with different oceanic thermal structures are designed to elucidate the responses of tropical cyclones to the ocean eddy and the effects of tropical cyclones on the ocean. This simple model shows that rapid intensification occurs as a storm encounters the ocean eddy because of enhanced heat flux. While strong winds usually cause strong mixing in the mixed layer and thus cool down the sea surface, negative feedback to the storm intensity of this kind is limited by the presence of a warm ocean eddy, which provides an insulating effect against the storm-induced mixing and cooling. Two eddy factors, FEDDY-S and FEDDY-T, are defined to evaluate the effect of the eddy on tropical cyclone intensity. The efficiency of the eddy feedback effect depends on both the oceanic structure and other environmental parameters, including properties of the tropical cyclone. Analysis of the functionality of FEDDY-T shows that the mixed layer depth associated with either the large-scale ocean or the eddy is the most important factor in determining the magnitude of eddy feedback effects. Next to them are the storm’s translation speed and the ambient relative humidity.

scholarly journals Formation Mechanisms of the Pacific–North American Teleconnection with and without Its Canonical Tropical Convection Pattern

2017 ◽  
Vol 30 (9) ◽  
pp. 3139-3155 ◽  
Author(s):  
Ying Dai ◽  
Steven B. Feldstein ◽  
Benkui Tan ◽  
Sukyoung Lee
Keyword(s):  
North American ◽  
Wave Train ◽  
Dominant Role ◽  
Teleconnection Pattern ◽  
Wave Activity ◽  
Tropical Convection ◽  
Formation Mechanisms ◽  
Convection Pattern ◽  
Pacific North American ◽  
The Pacific

The mechanisms that drive the Pacific–North American (PNA) teleconnection pattern with and without its canonical tropical convection pattern are investigated with daily ERA-Interim and NOAA OLR data (the former pattern is referred to as the convective PNA, and the latter pattern is referred to as the nonconvective PNA). Both the convective and nonconvective positive PNA are found to be preceded by wave activity fluxes associated with a Eurasian wave train. These wave activity fluxes enter the central subtropical Pacific, a location that is favorable for barotropic wave amplification, just prior to the rapid growth of the PNA. The wave activity fluxes are stronger for the positive nonconvective PNA, suggesting that barotropic amplification plays a greater role in its development. The negative convective PNA is also preceded by a Eurasian wave train, whereas the negative nonconvective PNA grows from the North Pacific contribution to a circumglobal teleconnection pattern. Driving by high-frequency eddy vorticity fluxes is largest for the negative convective PNA, indicating that a positive feedback may be playing a more dominant role in its development. The lifetimes of convective PNA events are found to be longer than those of nonconvective PNA events, with the former (latter) persisting for about three (two) weeks. Furthermore, the frequency of the positive (negative) convective PNA is about 40% (60%) greater than that of the positive (negative) nonconvective PNA.

scholarly journals Analysis of landslide triggering conditions in the Sarno area using a physically based model

2014 ◽  
Vol 18 (8) ◽  
pp. 3225-3237 ◽  
Author(s):  
G. Capparelli ◽  
P. Versace
Keyword(s):  
Dominant Role ◽  
Technical Literature ◽  
Subsurface Hydrology ◽  
Physically Based Model ◽  
Physically Based ◽  
Prone Area ◽  
Triggering Conditions ◽  
Slope Instabilities ◽  
Analytical Approaches

Abstract. Rainfall is recognized as a major precursor of many types of slope movements. The technical literature reports both study cases and models of landslides induced by rainfall. Subsurface hydrology has a dominant role since changes in the soil water content significantly affect the soil shear strength. The analytical approaches used are very different, ranging from statistical models to distributed and complete models. The latter take several components into account, including specific site conditions, mechanical, hydraulic and physical soil properties, local seepage conditions, and the contribution of these to soil strength. This paper reports a study using a complete model, named SUSHI (Saturated Unsaturated Simulation for Hillslope Instability), to simulate the role of subsurface hydrology in rain-induced landslides, on a case of great interest both in terms of its complexity and its severity. The landslide-prone area in question is located in Campania (southern Italy), where disastrous mudflows occurred in May 1998. The region has long been affected by rainfall-induced slope instabilities, which often involve large areas and affect many people. The application allows a better understanding of the role of rainfall infiltration and suction changes in the triggering mechanism of the phenomena. These changes must be carefully considered when assessing hazard levels and planning mitigation interventions regarding slope stability.

scholarly journals Examining Trends in Satellite-Detected Tropical Overshooting Tops as a Potential Predictor of Tropical Cyclone Rapid Intensification

2012 ◽  
Vol 51 (11) ◽  
pp. 1917-1930 ◽  
Author(s):  
Sarah A. Monette ◽  
Christopher S. Velden ◽  
Kyle S. Griffin ◽  
Christopher M. Rozoff
Keyword(s):  
North Atlantic ◽  
Detection Algorithm ◽  
Severe Weather ◽  
Forecast Skill ◽  
Rapid Intensification ◽  
Tropical Oceans ◽  
Independent Test ◽  
Cursory Examination ◽  
The Tropics ◽  
Initial Exploration

AbstractA geostationary satellite–derived cloud product that is based on a tropical-overshooting-top (TOT) detection algorithm is described for applications over tropical oceans. TOTs are identified using a modified version of a midlatitude overshooting-top detection algorithm developed for severe-weather applications. The algorithm is applied to identify TOT activity associated with Atlantic Ocean tropical cyclones (TCs). The detected TOTs can serve as a proxy for “hot towers,” which represent intense convection with possible links to TC rapid intensification (RI). The purpose of this study is to describe the adaptation of the midlatitude overshooting-top detection algorithm to the tropics and to provide an initial exploration of possible correlations between TOT trends in developing TCs and subsequent RI. This is followed by a cursory examination of the TOT parameter’s potential as a predictor of RI both on its own and in multiparameter RI forecast schemes. RI forecast skill potential is investigated by examining empirical thresholds of TOT activity and trends within prescribed radii of a large sample of developing North Atlantic TC centers. An independent test on Atlantic TCs in 2006–07 reveals that an empirically based TOT scheme has potential as a predictor for RI occurring in the subsequent 24 h, especially for RI maximum wind thresholds of 25 and 30 kt (24 h)−1 (1 kt ≈ 0.5 m s−1). As expected, the stand-alone TOT-based RI scheme is comparatively less accurate than existing objective multiparameter RI prediction methods. A preliminary experiment that adds TOT-based predictors to an objective logistic regression-based scheme is shown to improve slightly the forecast skill of RI, however.

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