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GERMAN POVEDA published an article in January 2014.
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(2001 - 2014)
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Article 0 Reads 24 Citations Seasonal precipitation patterns along pathways of South American low-level jets and aerial rivers Published: 01 January 2014
Water Resources Research, doi: 10.1002/2013wr014087
 We study the seasonal dynamics of the eastern Pacific (CHOCO) and Caribbean low‐level jets (LLJ), and aerial rivers (AR) acting on tropical and subtropical South America. Using the ERA‐Interim reanalysis (1979–2012), we show that the convergence of both LLJs over the eastern Pacific‐western Colombia contributes to the explanation of the region's world‐record rainfall. Diverse variables involved in the transport and storage of moisture permit the identification of an AR over northern South America involving a midtropospheric easterly jet that connects the Atlantic and Pacific Oceans across the Andes, with stronger activity in April to August. Other major seasonal AR pathways constitute part of a large gyre originating over the tropical North Atlantic, veering to the southeast over the eastern Andes and reaching regions of northern Argentina and southeastern Brazil. We illustrate the distribution of average seasonal precipitation along the LLJs and AR pathways with data from the Tropical Rainfall Measuring Mission (1998–2011), combined with considerations of CAPE, topography, and land cover. In addition, the theory of the biotic pump of atmospheric moisture (BiPAM) is tested at seasonal time scales, and found to hold in 8 out of 12 ARs, and 22 out of 32 forest‐covered tracks (64% in distance) along the ARs. Deviations from BiPAM's predictions of rainfall distribution are explained by the effects of topography, orography, and land cover types different from forests. Our results lend a strong observational support to the BiPAM theory at seasonal time scales over South American forested flat lands.
Article 0 Reads 33 Citations Hydro-climatic variability over the Andes of Colombia associated with ENSO: a review of climatic processes and their imp... Published: 30 October 2010
Climate Dynamics, doi: 10.1007/s00382-010-0931-y
The hydro-climatic variability of the Colombian Andes associated with El Niño–Southern Oscillation (ENSO) is reviewed using records of rainfall, river discharges, soil moisture, and a vegetation index (NDVI) as a surrogate for evapotranspiration. Anomalies in the components of the surface water balance during both phases of ENSO are quantified in terms of their sign, timing, and magnitude. During El Niño (La Niña), the region experiences negative (positive) anomalies in rainfall, river discharges (average and extremes), soil moisture, and NDVI. ENSO’s effects are phase-locked to the seasonal cycle, being stronger during December–February, and weaker during March–May. Besides, rainfall and river discharges anomalies show that the ENSO signal exhibits a westerly wave-like propagation, being stronger (weaker) and earlier (later) over the western (eastern) Andes. Soil moisture anomalies are land-cover type dependant, but overall they are enhanced by ENSO, showing very low values during El Niño (mainly during dry seasons), but saturation values during La Niña. A suite of large-scale and regional mechanisms cooperating at the ocean–atmosphere–land system are reviewed to explaining the identified hydro-climatic anomalies. This review contributes to an understanding of the hydro-climatic framework of a region identified as the most critical hotspot for biodiversity on Earth, and constitutes a wake-up call for scientists and policy-makers alike, to take actions and mobilize resources and minds to prevent the further destruction of the region’s valuable hydrologic and biodiversity resources and ecosystems. It also sheds lights towards the implementation of strategies and adaptation plans to coping with threats from global environmental change.
Article 0 Reads 10 Citations Improved long-term mean annual rainfall fields for Colombia Published: 07 October 2010
International Journal of Climatology, doi: 10.1002/joc.2232
With the aim of improving the long‐term mean annual surface water balance of Colombia, four new annual average precipitation fields are estimated at 4 km spatial resolution. To put in context, a concise literature review of rainfall in Colombia is presented. For estimation purposes, diverse multivariate geostatistical methods are implemented by combining information from 1180 raingauges covering the period 1950‐2005, and satellite data from the tropical rainfall measuring mission (TRMM) for the period 1999‐2005, used as a drift for the following geostatistical methods: (1) kriging with an external drift (KED), (2) standardized cokriging (SCK), (3) colocated cokriging (CCK), and (4) Markov regionalization CCK (CCKM). To ensure the reliability of the estimated precipitation fields, a detailed cross‐validation procedure is performed, including univariate and bivariate analyses of residuals, which allows us to conclude that the best estimated rainfall field is obtained with KED, and the worst with SCK. Visual analyses are also performed in the search for consistency of the resulting precipitation fields. Furthermore, local (at‐a‐pixel) uncertainty modelling analysis is performed using the indicator approach. Conditional cumulative distribution functions (CCDF) are estimated using indicator CCK with Bayes‐Markov hypothesis. Statistical descriptors for the pixel's CCDFs are estimated based on the resulting precipitation fields, including long‐term mean, conditional variance and the coefficient of variation. These improved precipitation fields along with their estimated uncertainties are available (http://cancerbero.unalmed.edu.co/∼hidrosig/index.php) for the scientific community and constitute useful basic information for diverse applications in water resources, agriculture, hydropower generation, human health, risks and disaster prevention, and many other applied sectors in Colombia. Copyright © 2010 Royal Meteorological Society
Article 0 Reads 4 Citations Diurnally driven scaling properties of Amazonian rainfall fields: Fourier spectra and order-qstatistical moments Published: 03 June 2009
Journal of Geophysical Research, doi: 10.1029/2008jd011281
 The influence of the diurnal cycle on spatial scaling properties of Amazonian rainfall fields is investigated using data gathered during the January–February 1999 Wet Season Atmospheric Meso‐scale Campaign in the state of Rondonia (Brazil, SW Amazonia). Most intense precipitation events with large spatial coverage occur during early afternoon. Amplitudes of average and maximum intensity diurnal cycles are higher during the easterly than during the westerly atmospheric regime. The diurnal cycle of average rainfall occupancy exhibits a significantly larger amplitude during the westerly regime. Storms exhibit power law Fourier spectra, E(k) = ck−β, with two scaling regimes characterized by different scaling exponents (β1 and β2), separated at a critical distance, which depends on the spatial extent of rainfall organization. Inversely correlated diurnal cycles for β1 and β2 reflect rainfall organization patterns at different spatial scales through the 24‐h period. The break occurs at smaller (larger) spatial scales during the morning (afternoon‐evening). Average values of c and β exhibit inversely related diurnal cycles, and different behavior during either atmospheric regime. Order‐q statistical moments indicate multiscaling of rainfall fields. Departures from simple scaling are also driven by the diurnal cycle, reflecting differences in convective activity and the spatial organization of rainfall throughout the 24‐h cycle. Departures from simple scaling are dependent on the moment order q. Clear‐cut differences between the estimated order‐q statistical moments appear during both atmospheric regimes. These results shed light toward linking physical processes with statistics in Amazonian storms.
Article 0 Reads 5 Citations Linear and global space-time dependence and Taylor hypotheses for rainfall in the tropical Andes Published: 23 May 2009
Journal of Geophysical Research, doi: 10.1029/2008jd011074
 The space‐time linear and global dependence of tropical rainfall in an intra‐Andean valley of Colombia is estimated using 15 min of resolution data, recorded by 18 raingauges, through correlation (ρ) and mutual information (MI) analysis of the entire record (1998–2006) and at seasonal and interannual (ENSO) timescales. Spatial dependence analyses are developed for increasing (1) time aggregation intervals T = 15 min to T = 24 hours, and (2) time lags τ = 15 min to τ = 120 min. Results for (1) indicate that both spatial MI and ρ decay as I(λ, T) = A(T)λ−α(T), but also that A(T) = aTμ and α(T) = bT−ω. Maps of MI and ρ for increasing values of T are discussed in terms of geographical and few known meteorological features. Regarding (2), exponential functions fit better the spatial decay rates of both MI and ρ, such that I(λ, τ) = F(τ)exp[−ϕ(τ)λ], with F(τ) = exp[−dτ], and ϕ(τ) = j−kτ. Maps of MI and ρ for increasing values of τ suggest that MI may be better suited than ρ to capture highly localized singularities of tropical mountain rainfall. Estimated power laws are highly dependent on both the seasonal cycle and ENSO phases, consistently with temporal dynamics of rainfall at both timescales. We tested the validity of Taylor hypothesis ρ(0, τ) = ρ(Uτ, 0) and found it rejected in 11 of 18 raingauges, which prompted us to introduce a global Taylor hypothesis using the space‐time MIs as I(0, τ) = I(Uτ, 0). Results indicate that power laws characterize the decay of both the temporal I(0, τ) and the space‐transformed I(λ, 0) with respect to τ. A rigorous statistical test indicates that the global Taylor hypothesis is valid in 14 of 18 raingauges within the 20–180 min time range.
Article 0 Reads 1 Citation Role of a simplified hydrological cycle and clouds in regulating the climate-biota system of Daisyworld Published: 01 April 2009
Tellus B: Chemical and Physical Meteorology, doi: 10.1111/j.1600-0889.2008.00411.x
The role of a simplified hydrological cycle and a physical representation of clouds is investigated in the Daisyworld model, subject to constant and variable solar forcing and varying cloud albedo and height. Under constant forcing, properties of the cloudy hydrologic cycle control the long-term system dynamics to non-oscillatory, oscillatory, abiotic or biotic states. In case of oscillatory solutions, their amplitude and periodicity are controlled by the net cooling or warming effects from clouds. Two conditions are considered under variable forcing—active or neutral—depending on the existence or not of biota–environment feedbacks. Temperature, cloudiness and hydrological variables are self-regulated in the active condition, whereas non-regulated in the neutral condition. Self-regulation is quantified through two measurements (luminosity range and total life), both of which can be larger in our model than in several other variants of Daisyworld, depending on cloud characteristics. The hydrological cycle and clouds can make the planet more habitable for life, independent of the capacity of the system for biological adaptation. Two hypotheses are put forward: (1) beneficial effects for life emerge from biota–clouds interactions, enhancing the global amount of life and extending the life span; and (ii) the existence of a maximum self-regulation capacity principle.DOI: 10.1111/j.1600-0889.2008.00411.x