Modern Climatology

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  01 Southern Hemisphere Tropical Cyclone Climatology

  Yuriy Kuleshov

  Southern Hemisphere Tropical Cyclone Climatology:

  Each year, around 80 tropical cyclones (TCs) form around the world, with about one-third of them in the Southern Hemisphere (SH) (Gray, 1979). Tropical cyclones within the South Indian Ocean (SIO) and the South Pacific Ocean (SPO) are frequent and intense, and they dramatically affect maritime navigation and the lives of communities in coastal areas. Australia and the island nations are affected each year by TCs. In extreme cases they can have devastating consequences on life, property and the economic well-being of the communities directly affected and the country as a whole, as in the case of one of Australia’s most notorious TCs, Tracy, which devastated Darwin, the capital of the Northern Territory, on 25 December 1974 (Australian Government, 1977).

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  02 Indian Monsoon Depression: Climatology and Variability

  Jin-Ho Yoon and Wan-Ru Huang

  The monsoon climate is traditionally characterized by large amount of seasonal rainfall and reversal of wind direction (e.g., Krishnamurti 1979). Most importantly this rainfall is the major source of fresh water to various human activities such as agriculture. The Indian subcontinent resides at the core of the Southeast Asian summer monsoon system with the monsoon trough extended from northern India across Indochina to the Western Tropical Pacific (WTP). Large fraction of annual rainfall occurs during the summer monsoon season, i.e., June – August1, with two distinct maxima. One is located over the Bay of Bengal with rainfall extending northwestward into eastern and central India, and the other along the west coast of India where the lower level moist wind meets the Western Ghat Mountains (Saha and Bavardeckar 1976). The rest of the Indian subcontinent receives relatively less rainfall.

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  03 Characteristics of the Quasi-16 Day Wave in the Mesosphere and Lower Thermosphere (MLT): A Review Over an Equatorial Station Thumba (8.50N, 76.50E)

  Siddarth Shankar Das

  To understand the climate variability and weather prediction in the Earth’s atmosphere, measurements of winds, temperature and wave activities are very crucial. The Earth’s atmosphere is believed to act as a source and sink for the waves of a broader spectrum with periods from few seconds to years. Generally, the Earth’s atmosphere is stably stratified except the planetary boundary layer and thus makes a reasonable assumption for the presence of atmospheric waves. A barotropic atmosphere in a resting basic state is able to support these spectra of waves. These waves move diagonally upward or downward and horizontally. The mean zonal circulation is mainly driven by these atmospheric waves, which are believed to be generated in the troposphere and propagates horizontally and vertically in to the middle and upper atmosphere. These waves transport energy and momentum from one region to another without the transport of material medium thereby impinging the signature of the source region on to the sink region. The waves propagating in Earth's atmosphere are expected to be both anisotropic and dispersive. The anisotropic characteristics of these waves mean that the properties of the waves are not uniform in all the directions. The propagating waves can be characterized by the amplitude and phase, which depends on time and space. When the wave frequency depends on the wavelength (2/K) then the wave is dispersive. For such waves the group velocity is different from the phase velocity. A better understanding of the vertical coupling by these wave activities will provide a deeper insight into the processes that control the dynamics and energetics of the whole atmosphere.

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  04 Thunderstorm and Lightning Climatology of Australia

  Yuriy Kuleshov

  Thunderstorms are spectacular but hazardous weather phenomena and the associated lightning and wind gusts can be very hazardous to people, buildings, and industry and utility assets. The thunderstorm hazards in Australia are in most respects similar to those in other countries, but some are worthy of special comment. In some instances, the effects of lightning initiated bushfires are so extreme that they are classified as natural disasters. The wildfires started by lightning are known locally in Australia as bushfire and grass fires, and these can cause extensive damage and loss of life. The ignition is caused by the lightning current in ground flashes, and firing is associated with low moisture contents of (potential) fine fuels such as duff in trees and dense grass, and the occurrence of multiple stroke currents and continuing current. During dry periods, lightning initiated grass fires are a major problem in inland areas, as are lightning initiated bushfires in remote forest areas. Once ignited, grass fires spread quickly, whereas in bushfires, ignition often starts as a small localised fire in or near the crown of the tree, and it may take a few hours for the fire to spread to other trees and to become an uncontrollable wildfire. Given the potential hazards associated with lightning, knowledge about spatial and temporal distributions of thunderstorm and lightning activity is of great importance for developing comprehensive protective measures.

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  05 The South American Monsoon System: Climatology and Variability

  Viviane B.S. Silva and Vernon E. Kousky

  A typical Monsoon System is characterized by a reversal in the low-level wind direction between summer and winter seasons, and distinct wet (summer) and dry (winter) periods. The changes in low-level atmospheric circulation are related to changes in the thermal contrast between oceans and continents. During summer, the air over continents is warmer and more convectively unstable than air over adjacent oceanic regions. Consequently, lower pressure occurs over land and higher pressure occurs over nearby oceanic areas. This pressure pattern causes low-level moist air to converge onto the land, resulting in precipitation, especially during the late afternoon and evening hours. During winter the temperature contrasts and low-level atmospheric circulation are reversed, resulting in dry conditions over continents.

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  06 Climatology of the U.S. Inter-Mountain West

  Shih-Yu (Simon) Wang and Robert R. Gillies

  The Inter-Mountain West (IMW) of North America is a region that lies between the Rocky Mountains to the east and the Cascades and Sierra Nevada to the west (Fig. 1). The climate of the IMW is generally semi-arid but this varies by location and elevation. An estimated 50- 80% of the IMW’s streams and rivers are fed by mountain snowpack (Marks and Winstral 2001), while the majority of the streams and rivers flow into desert sinks or closed-basin lakes such as the Great Salt Lake (Fig. 1). These streams and rivers create some agriculturally productive areas in the otherwise dry basins and mountain valleys. In particular, the Colorado River supplies water to the population-booming southwestern states and cities. Climate in the Colorado River Basin has been a subject of intense research due to its projected drying trend (Barnett and Pierce 2008). Change in winter precipitation regime (i.e. ratio between rainfall and snowfall) is also a subject of interest not only because its role in water resource but also its impact on recreational (ski) industry in the IMW.

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  07 Climatology of the Northern-Central Adriatic Sea

  Aniello Russo, Sandro Carniel, Mauro Sclavo, and Maja Krzelj

  It is well know that the ocean processes exert a great influence on global climate as well as affect the local climate of coastal areas (Russo et al., 2002). Within the Mediterranean region (see Fig. 1a), the presence of the Adriatic Sea influences the atmospheric properties of the surrounding regions over long and short time-scales, and has obviously a relevant influence on human activities and ecosystems (Boldrin et al., 2009).

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  08 Spatial and Temporal Variability of Sea Surface Temperature in the Yellow Sea and East China Sea over the Past 141 Years

  Daji Huang, Xiaobo Ni, Qisheng Tang, Xiaohua Zhu, and Dongfeng Xu

  The Yellow Sea and East China Sea (YES) are marginal seas in the northwest Pacific. There is in fact a smaller sea, the Bohai Sea, to the north of the Yellow Sea. For most discussions in the chapter, we shall treat the Bohai Sea as part of the Yellow Sea. The YES is one of the mostly intensively utilized sea in the world, for example, heavy fishery and marine aquaculture. The use of the YES is closely related to its climate variability, though it is not well-know because until now there has been a lack of adequate observational data. To know the climatology of sea surface temperature (SST, all the acronyms used in the chapter are listed in Table 1) in the YES and their relationship with regional and global climate have both scientific and social importance.

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  09 Paleotempestology: Reconstructing Atlantic Tropical Cyclone Tracks in the Pre-HURDAT Era

  Jill S.M. Coleman and Steven A. LaVoie

  The study of past tropical cyclone activity by means of geological proxies and/or historical documentary records is known as paleotempestology. This scientific discipline has become prominent over the course of the last decade partially in response to the recent increase in tropical cyclone count and intensity in the North Atlantic basin witnessed since 1995. The field has also developed due to the socioeconomic impacts of tropical cyclones particularly along vulnerable coastal regions. During the twenty-five years prior to the start of the most recent increase in hurricane activity, major (Category 3, 4, or 5) hurricanes were less frequent than in previous decades. Yet, property losses from the hurricanes that did make landfall in the United States increased during this period due to development in damage prone areas (NOAA Paleoclimatology Program, 2000). Many researchers hence stress the importance of identifying historical tropical cyclones to understand long term trends in tropical cyclone climatology and to determine the influence of anthropogenic global warming on tropical cyclone activity and intensity. The North Atlantic Hurricane Database (HURDAT) has been one of the authoritative sources for examining North Atlantic tropical cyclone activity trends since 1850. However, some of the deadliest known hurricanes and potentially most active seasons in the North Atlantic basin occurred prior to the beginning of the HURDAT record (Table 1), including the Great Hurricane of 1780 that killed an estimated 22,000 people and was one of eight known tropical cyclones during that season. This chapter will provide a brief overview of some paleotempestology techniques and illustrate a methodology for identifying and reconstructing historical North Atlantic tropical cyclone tracks in the pre-HURDAT era employing a Geographic Information System (GIS) and utilizing readily accessible archival data.

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  10 Cenozoic Climatic Record for Monsoonal Rainfall over the Indian Region

  Mohan Kuppusamy and Prosenjit Ghosh

  Atmospheric carbon dioxide level is one of the major drivers responsible for the global temperature change (Lacis et al., 2010). The role of carbon dioxide as an important greenhouse gas, and its contribution towards regulation of global surface temperature has been recognized for over a century (Arrhenius, 1896; Chamberlin, 1899; Royer, 2006). The ice core records along with other proxy based records provides an evidence signifying a strong coupling between CO2 and global temperature for at least the last ~65 m.y. (million years) (Petit et al., 1999; Siegenthaler et al., 2005, Zachos et al., 2001). The intensification of convective hydrological cycle inducing heavy rainfall during high pCO2 condition is both simulated and estimated from General Circulation Models (GCM) and geochemical analyses of fossil record respectively (Kutzbach & Gallimore, 1989). The evidences of intensification of monsoon, which refer to the rainfall due to seasonal reversal of the wind direction along the shore of the Indian Ocean especially in the Arabian Sea and surrounding regions, are preserved in the sedimentary records from continental and oceanic region (Fig.1). The other factor which affected the regional hydrological cycle apart from the concentration of CO2 in the atmosphere is tectonic rise of Himalayan mountain. Proxy record based on parameters like stomata index, alkenones and boron isotopes clearly suggested high concentration of CO2 in the atmosphere (~400 ppm) during Miocene time. The estimated concentration of CO2 observed in the atmosphere was rather similar to the concentration of CO2 in the atmosphere measured in the recent years at Mauna Loa (Thoning et al., 1989). The effect of such high CO2 concentration is seen to have significantly modulated and altered the pattern of rainfall distribution, intensity and its spatial variability. Record from sedimentary archives from the continental and marine sites over the Indian region yielded evidence of warmer, wetter and higher temperature seasonal climate for the Miocene period. A similarity of signature both from continental region and the marine archives support the argument for the change in hydrological condition during last 20 m.y. The marine records are only a few but the largely scattered along the continental margin and central Indian Ocean. A more recent study of such sedimentary sequences lying on the western and eastern India provided glimpses of spatial variability of regional climate. The chapter will narrate the long term variation in Miocene monsoonal rainfall and its spatial pattern using large set of available observations from the palaeo record.

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  11 Climate Change: Is It More Predictable Than We Think?

  Rafail V. Abramov

  The global climate systemties togethermany physical variables, such as flow velocity, density, pressure, temperature, to name a few. The core equations of the climate system are the primitive evolution equations of the atmosphere and ocean (Lions et al., 1992a;b; 1993a;b; 1995; Majda, 2003), which directly involve the flow velocity (or, alternatively, streamfunction and vorticity), density and pressure. To incorporate the effects of other relevant physical processes which supply the energy to or draw it from the motion of the flow, the primitive equations are coupled to other physical processes through temperature, water vapor, ocean surface pressure, and other variables. The coupling terms often preserve energy balance, that is, at any moment, the sum of energy transfer rates between all coupled processes is zero. The main difficulty in the study of the behavior of primitive equations lies in the nonlinearity of the dynamics of velocity or streamfunction-vorticity in the advection term. The nonlinearity of the primitive equations is also the main source of chaos and lack of predictability for long times in the weather and climate prediction. As has first been recognized by Lorenz (1963), even a simple three-variable nonlinear dynamical system (the so-called Lorenz attractor), based on the idealized convection cell with cooling at the top and heating at the bottom, exhibits extreme sensitivity to initial conditions. Nowadays, the Lorenz attractor is considered a canonical textbook example of chaos in a nonlinear dynamical system, with many illustrations depicting two nearly identical initial conditions evolving into two unrelated trajectories after a short period of time. In more complex dynamical systems with advection terms, nonlinear chaos develops in much more sophisticated fashion, making long-term forecasts difficult and uncertain.

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  12 On the Relationship Between Boundary Layer Convergence and Cloud-to-Ground Lightning

  Michael L. Gauthier

  It is generally accepted that significant electrification, and subsequent lightning generation, in clouds is attained via non-inductive charging (NIC) when sufficient numbers of ice crystals collide with graupel particles in the presence of supercooled liquid water [e.g. Saunders et al., 1991; Jayaratne et al., 1983; Takahashi, 1978]. As these particle scale interactions are driven by vertical motions it can be argued that, under appropriate thermodynamical and microphysical conditions, any process that enhances updraft strength should also enhance the storms ability to generate lightning. Constrained by mass continuity, updrafts leading to deep moist convection are necessarily associated with sub-cloud horizontal mass convergence. Given that the Earth’s surface is impermeable with respect to the wind, it is clear that horizontal convergence of boundary layer winds should result in compensating upward vertical motions with greater convergence over a given area resulting in greater vertical motions, possibly capable of initiating and/or intensifying convection. All else being equal (i.e., sufficient moisture and instability requisite for the development of deep moist convection), enhancements in boundary layer convergence (BLC) should deepen the planetary boundary layer (PBL), thereby enhancing the instability, with the end result being an increase in the number of updrafts capable of breaking the “cap” (capping inversion) allowing for more vigorous interactions between precipitation sized ice particles and ascending ice crystals within the charging zone, ultimately resulting in enhancements in thunderstorm electrification and lightning via NIC.

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  13 Synthesizing High-Resolution Climatological Wind Fields with a Mesoscale Atmospheric Boundary Layer Model Forced with Local Weather Observations

  Guillermo J. Berri

  The region of the La Plata River in southeastern South America (see Fig. 1) concentrates important economic and social activities since one third of the population of Argentina and more than one half the population of Uruguay live there. Large urban complexes, different commercial activities and important industries are located along its shores. In addition, the La Plata River and its tributary the Paraná River are main ship tracks with some of the largest ports of the southern cone of South America. Therefore, the region is of vital importance for the two countries. The La Plata River is a large water surface that projects into the continent, conditioning the local weather and climate. Thus, other related environmental aspects are strongly influenced by the local weather and climate conditions, such as environmental pollution, water currents and tidal regime, commercial fishing at the oceanic front, port operations, navigation and tourism.

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  14 Rainfall Prediction Using Teleconnection Patterns Through the Application of Artificial Neural Networks

  Gholam Abbas Fallah-Ghalhari

  All aspects of human life are, directly or indirectly, affected by climatic processes. This effect is especially noticeable in such fields as agriculture, irrigation, economy, telecommunications, transportation, traffic, air pollution and military industries (Haltiner & Williams 1980). A number of researchers have studied the possibility of forecasting rainfall several months in advance using climate indices such as SOI, PDOI and NPI (e.g. Silverman and Dracup 2000). A well-known atmospheric phenomenon is the Southern Oscillation (SO). The SO is an atmospheric see-saw process in the tropical Pacific sea level pressure between the eastern and western hemispheres associated with the El Niño and La Niña oceanographic features. The oscillation can be characterized by a simple index, the Southern Oscillation Index (SOI). (Kawamura et al., 1998). The Pacific Decadal Oscillation index (PDOI) is the leading principal component of monthly sea surface temperature (SST) anomalies in the North Pacific Ocean north of 20°N (Zhang et al., 1997; Mantua et al., 1997). Trenberth and Hurrell (1994) have defined the North Pacific Index (NPI) as the area-weighted sea level pressure over the region 30°N to 65°N, 160°E to 140°W to measure the decadal variations of atmosphere and ocean in the north Pacific.

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  Modern Climatology - Full Text

  Shih-Yu (Simon) Wang and Robert R. Gillies

  Climatology, the study of climate, is no longer regarded as a single discipline that treats climate as something that fluctuates only within the unchanging boundaries described by historical statistics. The field has recognized that climate is something that changes continually under the influence of physical and biological forces and so, cannot be understood in isolation but rather, is one that includes diverse scientific disciplines that play their role in understanding a highly complex coupled “whole system” that is the Earth’s climate. The modern era of climatology is echoed in this book. On the one hand it offers a broad synoptic perspective but also considers the regional standpoint as it is this that affects what people need from climatology, albeit water resource managers or engineers etc. Aspects on the topic of climate change – what is often considered a contradiction in terms – is also addressed. It is all too evident these days that what recent work in climatology has revealed carries profound implications for economic and social policy; it is with these in mind that the final chapters consider acumens as to the application of what has been learned to date. This book is divided into four sections that cover sub-disciplines in climatology. The first section contains four chapters that pertain to synoptic climatology, i.e., the study of weather disturbances including hurricanes, monsoon depressions, synoptic waves, and severe thunderstorms; these weather systems directly impact humanity. The second section on regional climatology has four chapters that describe the climate features within physiographically defined areas. The third section is on climate change which involves both past (paleoclimate) and future climate: The first two chapters cover certain facets of paleoclimate while the third is centered towards the signals (observed or otherwise) of climate change. The fourth and final section broaches the sub-discipline that is often referred to as applied climatology; this represents the important goal of all studies in climatology–one that affects modes of living. Here, three chapters are devoted towards the application of climatological research that might have useful application for operational purposes in industrial, manufacturing, agricultural, technological and environmental affairs.

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