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Ecology
Published in Robin Lovelace, Jakub Nowosad, Jannes Muenchow, Geocomputation with R, 2019
Robin Lovelace, Jakub Nowosad, Jannes Muenchow
Fog oases are one of the most fascinating vegetation formations we have ever encountered. These formations, locally termed lomas, develop on mountains along the coastal deserts of Peru and Chile.1 The deserts’ extreme conditions and remoteness provide the habitat for a unique ecosystem, including species endemic to the fog oases. Despite the arid conditions and low levels of precipitation of around 30–50 mm per year on average, fog deposition increases the amount of water available to plants during austal winter. This results in green southern-facing mountain slopes along the coastal strip of Peru (Figure 14.1). This fog, which develops below the temperature inversion caused by the cold Humboldt current in austral winter, provides the name for this habitat. Every few years, the El Niño phenomenon brings torrential rainfall to this sun-baked environment (Dillon et al., 2003). This causes the desert to bloom, and provides tree seedlings a chance to develop roots long enough to survive the following arid conditions.
Ocean Oscillation and Drought Indices: Principles
Published in Saeid Eslamian, Faezeh Eslamian, Handbook of Drought and Water Scarcity, 2017
Perhaps the largest of the upwelling zones is the Peruvian current system, also known as the “Humboldt current,” which is an arm of the West Wind Drift that flows eastward up the western coast of South America south of latitude 40°S, bringing cold Antarctic water to the surface along the coast of Ecuador, Chile, and Peru, while most of it continues through the Drake Passage around the southern tip of South America to the Atlantic. However, a shallow stream turns north to parallel the continent as far as latitude 4°S, where it turns west to join the Pacific South Equatorial Current. The Peruvian current, which is a relatively slow and shallow current with a width of about 900 km and transporting only 10,000,000–20,000,000 m3 of water per second, is often cold, except at times of El Niño every few years when the winds shift and the water in the Pacific Ocean gets warmer than usual, sloshing back and forth around the equator and interacting with winds above to cause weather changes worldwide. El Niño is the antithesis of upwelling along the Peruvian coast. During an abnormal Southern Hemisphere summer, coastal upwelling ceases and the strip of cool coastal water vanishes due to an exceptional weakness of the southeast trade winds and a displacement of the ITCZ southward beyond the equator.
Hydrological Modeling to Assess Runoff in a Semi-arid Andean Headwater Catchment for Water Management in Central Chile
Published in Diego A. Rivera, Alex Godoy-Faundez, Mario Lillo-Saavedra, Andean Hydrology, 2018
S. Penedo-Julien, A. Nauditt, A. Künne, M. Souvignet, P. Krause
The UHB is located within the Coquimbo region and has a drainage area of 670 km2 (see Fig. 10.66). The elevation varies from 2,000 to 5,500 m a.s.l. with a mean elevation of 3,724. According to the Köppen-Geiger classification the UHB belongs to the Bsk subgroup which is characterized by a long dry season (7-10 months) and that precipitation is less than potential evapotranspiration (Souvignet, 2010). The regional climate is driven by three main factors: (i) the southeast Pacific anticyclone, (ii) the cold Humboldt Current along the Pacific coast, (ii) the mountain range of the Andes (Oyarzún et al., 2003). Precipitation and temperature patterns follow an E-W axis driven by changes in altitude. Mean annual precipitation, including snowfall, for the period 1979-2006 measured at Hurtado was 147 mm concentrating in the winter months of June and July. The dry season goes from September until April. Precipitation is strongly influenced by orography, El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) contributing to a high inter- and intra-annual variability (Souvignet, 2010; Núñez et al., 2013). For instance, ENSO events can multiply annual precipitation by a factor of 2–3 (Oyarzún et al., 2003). Moreover, local basin features such as valley orientation, hill slope exposure, abrupt elevation changes result in relevant, small-scale variability in precipitation and snow accumulation spatial patterns (Favier et al., 2009). Mean annual temperature, also measured at Hurtado for the same period, was 17°C reaching its minimum in July (13°C), coinciding with the precipitation maximum, while the maximum temperature was reached in February (21°C).
Frictional effects in wind-driven ocean currents
Published in Geophysical & Astrophysical Fluid Dynamics, 2021
The ocean covers more than 70% of the Earth's surface and is the largest solar energy collector on Earth. As water can absorb large amounts of heat without a large increase in temperature, the oceans are Earth's largest thermal reservoir, with the upper 3 m of the ocean storing as much heat as the overlying atmosphere (see Gill 2018). Also, more than 80% of the Earth's thermal imbalance due to the anthropogenic forcing has been absorbed by the ocean (see Levitus et al.2012) and the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report revealed that the ocean has absorbed 93% of the extra energy from the enhanced greenhouse effect. This is especially relevant since the rate of global warming is determined mainly by the increase of anthropogenic greenhouse gases and the ocean heat uptake, with most of the increase in temperature concentrated in the ocean's upper 100 m (see Levitus et al.2012). Moreover, the rate of warming of the upper ocean is currently larger than that of the deep ocean (see Marshall and Zanna 2014). The tremendous ability to store and release heat over long periods of time gives the ocean a central rôle in stabilising the climate, with the ocean currents helping to counteract the uneven distribution of solar radiation reaching Earth's surface (see Marshall and Plumb 2016). While the thermohaline circulation due to deep-ocean currents has an impact on climate (see Vallis 2005), the heat transport due to surface ocean currents is also a key the factor in regulating the global climate. Surface ocean currents can occur on local to global scales and are typically wind-driven, their effect being mainly confined to the top 400 m of the ocean. Note that the horizontal mass transport induced by wind-drift currents generates vertical movement throughout the upper 1 km of the ocean since these transports converge in some regions and diverge in others, and mass conservation brings about the development of vertical flow to replace or remove the diverging/converging water masses; for example, the convergence occurring throughout the subtropical North Pacific is associated with downwelling, while the divergence in the subpolar North Pacific is related to upwelling (see Talley et al.2011). Even though the horizontal velocities of ocean flows, typically of the order of , are about a factor larger than the vertical velocities (see Viúdez and Dritschel 2003), downwelling is a key process in the transfer of energy from the surface to the interior of the oceans (see Roquet et al.2011). Since surface currents can carry warmed or cooled water as far as several thousand kilometres (for example, the warm Gulf Stream in the North Atlantic or the cold Humboldt current in the South Pacific), an apparently small change in just one aspect of the ocean's behaviour can produce major climate variations over large areas. A better conceptual understanding of the generation of surface currents, based on models that represent the main physical processes more realistically, is therefore relevant for climate studies.