scholarly journals Impact de la variabilité climatique et de l'anthropisation sur les écoulements de la Bénoué (nord Cameroun)

2021 ◽  
Vol 384 ◽  
pp. 261-267
Author(s):  
Valentin Brice Ebodé ◽  
Gil Mahé ◽  
Ernest Amoussou
Keyword(s):  
Central Africa ◽  
Hydrological Regime ◽  
Wet Season ◽  
Time Step ◽  
Water Storage Capacity ◽  
Surface Areas ◽  
Afrique Tropicale ◽  
Afrique Centrale ◽  
The Mean ◽  
Annual Time

Abstract. La sécheresse observée en Afrique tropicale vers la fin des années 1960, a également affecté le bassin de la Bénoué en Afrique centrale, avec une persistance remarquable qui s'est répercutée sur les écoulements. Les ruptures à la baisse ont été mises en évidence dans les séries hydropluviométriques de ce bassin au pas de temps annuel en 1970–1971 (pluies) et 1971–1972 (débits). Les déficits associés à cette rupture sont de -2,9 % pour les pluies et -14,2 % pour les débits, par rapport à la moyenne climatologique (1950–1951 à 2014–2015). La saison humide a connu des évolutions pratiquement identiques. Cependant, depuis la décennie 1990, il est observé un relèvement significatif dans les écoulements moyens annuels de ce cours d'eau, et cela coïncide avec le retour des pluies. Le maintien de cette hausse au cours des récentes décennies pourrait être envisagé en raison de l'accroissement des espaces imperméabilisés dans le bassin, qui compenseraient le déficit engendré par la rechute des pluies après la décennie 1990 via une accentuation du ruissèlement. De plus, depuis la mise en eau du barrage de Lagdo en 1983, il est observé non seulement une augmentation de l'ensemble des gammes de débits minima suivant des taux allant de +57,8 % (minimum sur 1 jour) à +70,1 % (minimum sur 90 jours), mais aussi un accroissement général de la variabilité de l'ensemble des débits extrêmes (minima et maxima). L'augmentation progressive du stockage en saison de pluies à la retenue de Lagdo, pour fournir l'électricité et l'eau d'irrigation durant la saison sèche à une population grandissante, rendent imperceptibles les effets de l'accroissement des espaces imperméabilisés non seulement sur les écoulements de la saison humide, mais aussi sur les écoulements maxima. Au demeurant, l'opérationnalisation du barrage de Lagdo a eu un impact significatif sur le régime de la Bénoué, se traduisant essentiellement par le caractère désormais permanent de l'écoulement tout au long de l'année hydrologique et un important fléchissement de la crue d'août à octobre. Abstract. A tendency to drought conditions appeared in tropical Africa from the end of 1960s, also affect the Benoue watershed in central Africa, with a remarkable persistence in streamflow. Negative breakpoints are found in the annual hydroclimatic time series of the Benoue catchment at annual time step in 1970–1971 for rainfall, and in 1971–1972 for discharges. Compared to the climatological mean (1950–1951 to 2014–2015), the deficits associated with these negative breakpoints are approximating −2.9 % for rainfall, and −14.2 % for discharges. The wet season shows similar developments. However, from the 1990s, there has been a significant increase in the mean annual discharges of the Benoue River, which coincides with that of the rainfall during the same decade. The maintenance of this increase over the recent decades could also be expected in response to an increase in impervious surface areas (ISA) in the catchment area, which could compensate the deficit generated by the post-1990s rainfall deficit through increasing in runoff. From the watering of the Lagdo dam in 1983, an increase in all ranges of minimum flow, ranging from +57.8 % (1 d minimum) to +70.1 % (90 d minimum), as well as an increase in the variability of extreme flows (minima and maxima), has been detected. During the wet season, the increase in water storage capacity at the Lagdo reservoir, which is used to provide electricity and irrigation water to a growing population, mitigates the increase in runoff, especially in maximum runoff. Moreover, the operationalization of the Lagdo dam has a significant impact on the Benoue hydrological regime, resulting mainly in a new perennial nature of the flow, and a significant decrease in flood from August to October.

Regional integration and free movement in Central Africa Integración regional y libre circulación en África Central L'intégration régionale et la libre circulation en Afrique centrale

2013 ◽  
Vol 3 (3) ◽  
pp. 123-140 ◽  
Author(s):  
Guy Marcel Nono
Keyword(s):  
Social Policy ◽  
Regional Integration ◽  
Central Africa ◽  
Regional Level ◽  
Free Movement ◽  
African Union ◽  
Colonial History ◽  
Political Debate ◽  
Politique Sociale ◽  
Afrique Centrale

A pillar of African emergence and an important issue of political debate that is central to regional integration, free movement is however not yet acquired in Central Africa. Yet a glance at the pre colonial history invites us to believe that Central Africa has been an area of free movement. The recognition of a right that cannot be realized only by an agreement leads to the Central African states pledging to work together in the context of regional integration by recognizing their citizens' right to full mobility. This contribution highlights the efforts, challenges and prospects of free movement in Central Africa by reference to the African Union framework, and asks if the legal and institutional framework of free movement in Central Africa has led to the emergence of a social policy supportive of free movement at the sub regional level. Spanish La libre circulación de personas es un pilar del África emergente, un tema importante en el debate político, un punto central de la integración regional, y sin embargo todavía intangible en África Central. No obstante, una mirada a la historia precolonial nos invita a pensar que África Central ha sido un espacio de libre circulación. El reconocimiento de un derecho que no puede realizarse sólo por un acuerdo, conduce a que los Estados de África Central se comprometan a trabajar juntos en el marco de la integración regional para reconocer el derecho de sus ciudadanos a la movilidad total. Esta contribución destaca los esfuerzos, desafíos y perspectivas de la libre circulación en África Central en referencia con el marco de la Unión Africana, y se pregunta si el marco legal e institucional de la libre circulación en África Central ha llevado a la aparición de una política social que apoye la libre circulación a nivel subregional. French Pilier de l'émergence de l'Afrique, enjeu des débats politiques et de l'intégration, la libre circulation n'est pas encore un acquis en Afrique Centrale. Pourtant, un regard porté sur l'histoire précoloniale nous invite à croire que l'Afrique centrale a été un espace de libre circulation. La reconnaissance d'un droit ne pouvant se faire que par l'objet d'un accord, les États d'Afrique Centrale se sont engagés dans le choix d'une histoire à réaliser ensemble dans le cadre de l'intégration, en consacrant dans des pactes communautaires la pleine mobilité de leurs ressortissants. Cette contribution met en évidence les efforts, défis et perspectives de la libre circulation en Afrique centrale par référence au cadre de l'Union africaine, et pose la question de savoir si le cadre juridique et institutionnel de la libre circulation en Afrique centrale a conduit à l'émergence d'une politique sociale en faveur de la libre circulation au niveau sous régional.

60 Contact Hand Burns in Children: Still a Major Prevention Need

2020 ◽  
Vol 41 (Supplement_1) ◽  
pp. S39-S40
Author(s):  
Jaclyn M McBride ◽  
Kathleen S Romanowski ◽  
Soman Sen ◽  
Tina L Palmieri ◽  
David G Greenhalgh
Keyword(s):  
Graft Loss ◽  
Dorsal Surface ◽  
Skin Grafting ◽  
Secondary Surgery ◽  
Surface Areas ◽  
Palmar Surface ◽  
The Mean ◽  
Total Body ◽  
Hand Burns ◽  
Palmar Aspect

Abstract Introduction Since toddlers explore with their hands, contact burns continue to be a major pediatric problem. The purpose of this report is to review a pediatric burn unit’s 8-year experience with contact burns of the hand. Methods After IRB approval, a review of pediatric contact hand burns that occurred between 2006–2014 was performed. We examined the causes and outcomes in pediatric contact hand burns in a single pediatric burn program. Results In the 8-year span, 535 children suffered contact burns to the hand (67 per year). The majority suffered hands burns from an oven or stove (120). The other etiologies included burns from a fireplace (76), clothing iron (65), curling or straightening iron (50), and firepit or campfire (46). The mean age at time of injury was 2.62 years old, with a range of 2 months old to18 years old. Male children (339) typically burned their hands more than females (197). Locations of injury included the palmar surface, dorsal surface, fingers tips/thumb, wrist or a combination of several different areas. Most children burned the palmar aspect of their hand (384) compared to the dorsal aspect (61). These burns typically cover small total body surface areas (mean 1.08% TBSA), with only 2% of burns comprising >5% TBSA. Approximately, 84% of these patients did not need surgery, but 86 (16%) had skin grafting (usually full-thickness) and 26% needed a secondary surgery. Of those that needed more than two, the average number of procedures was 3.6. Approximately 4.1% of patients needed a tertiary surgery. Causes for tertiary surgeries included contractures and graft loss. Out of twenty-two patients that needed a third surgery, 59% were due to graft loss and 41% were due to contractures. Conclusions Contact burns to the hand continue to be a major problem for toddlers. Children are most likely to burn themselves on an oven or stove, fireplace, clothing iron or curling/straightening iron. The palmar surface of the hand is the most likely site. While most children do not require surgery, approximately 16% require grafting. A significant number of those patients need reconstructive surgery. Clearly, current prevention efforts have failed to reduce these injuries. Applicability of Research to Practice Palm burns are common in young children. Efforts should focus on preventing these injuries.

scholarly journals Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

2018 ◽  
Vol 31 (23) ◽  
pp. 9719-9738 ◽  
Author(s):  
Caroline M. Dunning ◽  
Emily Black ◽  
Richard P. Allan
Keyword(s):  
Southern Africa ◽  
Crop Yields ◽  
Central Africa ◽  
Cmip5 Models ◽  
Future Climate Change ◽  
Boreal Summer ◽  
Wet Season ◽  
Socioeconomic Impacts ◽  
Continental Scale ◽  
Rainfall Frequency

Changes in the seasonality of precipitation over Africa have high potential for detrimental socioeconomic impacts due to high societal dependence upon seasonal rainfall. Here, for the first time we conduct a continental-scale analysis of changes in wet season characteristics under the RCP4.5 and RCP8.5 climate projection scenarios across an ensemble of CMIP5 models using an objective methodology to determine the onset and cessation of the wet season. A delay in the wet season over West Africa and the Sahel of over 5–10 days on average, and later onset of the wet season over southern Africa, is identified and associated with increasing strength of the Saharan heat low in late boreal summer and a northward shift in the position of the tropical rain belt over August–December. Over the Horn of Africa rainfall during the “short rains” season is projected to increase by over 100 mm on average by the end of the twenty-first century under the RCP8.5 scenario. Average rainfall per rainy day is projected to increase, while the number of rainy days in the wet season declines in regions of stable or declining rainfall (western and southern Africa) and remains constant in central Africa, where rainfall is projected to increase. Adaptation strategies should account for shorter wet seasons, increasing rainfall intensity, and decreasing rainfall frequency, which will have implications for crop yields and surface water supplies.

scholarly journals Phylogeographical and Evolutionary History of Variola major Virus; A Question of Timescales?

2020 ◽  
Author(s):  
Annalisa Bergna ◽  
Carla Della Ventura ◽  
Rossella Marzo ◽  
Massimo Ciccozzi ◽  
Massimo Galli ◽  
...  
Keyword(s):  
Far East ◽  
Central Africa ◽  
Colonial History ◽  
Short Term ◽  
The Far East ◽  
Sampling Locations ◽  
Whole Genomes ◽  
History Of ◽  
The Mean ◽  
Eastern And Southern Africa

In order to reconstruct the origin and pathways of variola virus (VARV) dispersion, we analyzed 47 VARV isolates available in public databases and their SNPs. The mean substitution rate of the whole genomes was 9.41x10-6 (95%HPD:8.5-11.3x10-6) substitutions/site/year. The time of the tree root was estimated to be a mean 68 years (95%HPD:60.5–75.9). The phylogeographical analysis showed that the Far East and India were the most probable locations of the tree root and of the inner nodes, respectively, whereas for the outer nodes it corresponded to the sampling locations. The Bayesian Skyline plot showed that the effective number of infections started to grow exponentially in 1915-1920, peaked in the 1940s, and then decreased to zero. Our results suggests that the VARV major strains circulating between 1940s-1970s probably shared a common ancestor originated in the Far East; subsequently moved to India, which became the center of its dispersion to eastern and southern Africa, and then to central Africa and the Middle East, probably following the movements of people between south-eastern Asia and the other places with a common colonial history. These findings may help to explain the controversial reconstructions of the history of VARV obtained using long- and short- term calibrations.

scholarly journals Investigation of Heavy Metals Level in selected Boreholes around the Vicinity of some Cemeteries in Benin City, Nigeria

2021 ◽  
Vol 25 (5) ◽  
pp. 841-845
Author(s):  
C.A.E. Ibhadode ◽  
I.R. Ilaboya
Keyword(s):  
Heavy Metals ◽  
Pollution Index ◽  
Mean Value ◽  
Dry Season ◽  
Wet Season ◽  
Monthly Basis ◽  
Benin City ◽  
Standard Procedures ◽  
The Mean ◽  
Mean Concentration

Groundwater pollution by heavy metals such as lead, copper, nickel and iron is one of the major environmental issues of concern which has developed into a widely studied area. In this study, attempt was made to investigate the level of heavy metals in selected boreholes around the vicinity of cemeteries in Benin City. Seventy-two (72) samples of groundwater were taken from boreholes in 9 stations around the three cemeteries in Benin City on monthly basis. The samples were analysed for 7 heavy metals, in accordance with standard procedures. The heavy metals include; Zinc, Lead Iron, Copper, Cadmium, Nickel and Mercury. From the results of the study, a variation in the mean concentration of zinc was observed. The mean concentration of zinc in site 1 was 0.450mg/l, for site 2, it was 0.140mg/l and for site 3, it was 1.0533mg/l. For iron, mean concentration was 0.072mg/l in site 1. For site 2, mean concentration of iron was 2.140mg/l and for site 3, mean concentration of iron was 0.560mg/l. It was further revealed based on the results that mean value of heavy metals in groundwater around cemeteries in Benin City were generally lower during dry season compared to wet season. In addition, result of computed pollution index (Pi) revealed that the heavy metal with the highest potential to pollute groundwater is Cadmium, with Pi of 0.5333 and 0.400 representing dry season and wet season respectively.

scholarly journals Mechanisms for an Amplified Precipitation Seasonal Cycle in the U.S. West Coast under Global Warming

2019 ◽  
Vol 32 (15) ◽  
pp. 4681-4698 ◽  
Author(s):  
Lu Dong ◽  
L. Ruby Leung ◽  
Jian Lu ◽  
Fengfei Song
Keyword(s):  
West Coast ◽  
Seasonal Cycle ◽  
Hydrological Cycle ◽  
Coupled Model ◽  
Wet Season ◽  
Thermal Contrast ◽  
Budget Analysis ◽  
The Mean ◽  
Underlying Mechanisms ◽  
The U.S

Abstract The mean precipitation along the U.S. West Coast exhibits a pronounced seasonality change under warming. Here we explore the characteristics of the seasonality change and investigate the underlying mechanisms, with a focus on quantifying the roles of moisture (thermodynamic) versus circulation (dynamic). The multimodel simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) show a simple “wet-get-wetter” response over Washington and Oregon but a sharpened seasonal cycle marked by a stronger and narrower wet season over California. Moisture budget analysis shows that changes in both regions are predominantly caused by changes in the mean moisture convergence. The thermodynamic effect due to the mass convergence of increased moisture dominates the wet-get-wetter response over Washington and Oregon. In contrast, mean zonal moisture advection due to seasonally dependent changes in land–sea moisture contrast originating from the nonlinear Clausius–Clapeyron relation dominates the sharpened wet season over California. More specifically, the stronger climatological land–sea thermal contrast in winter with warmer ocean than land results in more moisture increase over ocean than land under warming and hence wet advection to California. However, in fall and spring, the future change of land–sea thermal contrast with larger warming over land than ocean induces an opposite moisture gradient and hence dry advection to California. These results have important implications for projecting changes in the hydrological cycle of the U.S. West Coast.

scholarly journals Greening Trends of Southern China Confirmed by GRACE

2020 ◽  
Vol 12 (2) ◽  
pp. 328 ◽  
Author(s):  
Le Chang ◽  
Wenke Sun
Keyword(s):  
Storage Capacity ◽  
Southern China ◽  
Water Storage ◽  
Mass Change ◽  
Study Region ◽  
Change Rate ◽  
Water Storage Capacity ◽  
Source Data ◽  
The Mean ◽  
Gravity Recovery

As reported by the National Aeronautics and Space Administration (NASA), the world has been greening over the last two decades, with the highest greening occurring in China and India. The increasing vegetation will increase plant tissue accumulation and water storage capacity, and all of these variations will cause mass change. In this study, we found that the mass change related to greening in Southern China could be confirmed by Gravity Recovery and Climate Experiment (GRACE) observations. The mean mass change rate detected by GRACE is 6.7 ± 0.8 mm/yr in equivalent water height during 2003–2016 in our study region. This is consistent with the sum of vegetation tissue, soil water and groundwater change calculated using multi-source data. The vegetation accumulation is approximately 3.8 ± 1.3 mm/yr, which is the major contribution to region mass change. We also found that the change of water storage capacity related to vegetation can be detected by GRACE.

scholarly journals Modelling seasonal nitrate concentrations in runoff of a heathland catchment in SW Norway using the MAGIC model: I. Calibration and specification of nitrogen processes

2009 ◽  
Vol 40 (2-3) ◽  
pp. 198-216 ◽  
Author(s):  
Anne Merete S. Sjøeng ◽  
Richard F. Wright ◽  
Øyvind Kaste
Keyword(s):  
Acidic Deposition ◽  
N Deposition ◽  
Snow Accumulation ◽  
Long Term Effects ◽  
Time Step ◽  
Surface Water Chemistry ◽  
Magic Model ◽  
Best Fit ◽  
Annual Time

MAGIC (the Model of Acidification of Groundwater In Catchments) has been widely applied on catchments all over the world. The model has been used with annual time resolution to simulate the long-term effects of acidic deposition on surface water chemistry. Here MAGIC was applied using a monthly time step. The purpose was to simulate observed seasonal nitrate (NO3) concentrations and fluxes at an upland heathland catchment in southwestern Norway during the period 1993–2004. The rates of the key ecosystem nitrogen (N) processes (mineralization, plant uptake, litterfall and immobilization) were assumed to be governed by temperature. A snow accumulation and melt routine was used. The rates were calibrated to obtain the best match between the observed and simulated NO3 patterns. The best fit was obtained with standard yearly cycles for deposition and N parameters. The results show that MAGIC can explain 68 and 88% of the variation in seasonal NO3 concentrations and fluxes, respectively. The calibrated model provides a tool for exploring the effects of future scenarios of climate change and N deposition on NO3 in streamwater.

scholarly journals Aircraft observations of the chemical composition and aging of aerosol in the Manaus urban plume during GoAmazon 2014/5

2018 ◽  
Vol 18 (14) ◽  
pp. 10773-10797 ◽  
Author(s):  
John E. Shilling ◽  
Mikhail S. Pekour ◽  
Edward C. Fortner ◽  
Paulo Artaxo ◽  
Suzane de Sá ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Oxidation State ◽  
Biomass Burning ◽  
Urban Pollution ◽  
Organic Aerosol ◽  
Dry Season ◽  
Carbon Oxidation ◽  
Wet Season ◽  
The Mean ◽  
American Cities

Abstract. The Green Ocean Amazon (GoAmazon 2014/5) campaign, conducted from January 2014 to December 2015 in the vicinity of Manaus, Brazil, was designed to study the aerosol life cycle and aerosol–cloud interactions in both pristine and anthropogenically influenced conditions. As part of this campaign, the U.S. Department of Energy (DOE) Gulfstream 1 (G-1) research aircraft was deployed from 17 February to 25 March 2014 (wet season) and 6 September to 5 October 2014 (dry season) to investigate aerosol and cloud properties aloft. Here, we present results from the G-1 deployments focusing on measurements of the aerosol chemical composition and secondary organic aerosol (SOA) formation and aging. In the first portion of the paper, we provide an overview of the data and compare and contrast the data from the wet and dry season. Organic aerosol (OA) dominates the deployment-averaged chemical composition, comprising 80 % of the non-refractory PM1 aerosol mass, with sulfate comprising 14 %, nitrate 2 %, and ammonium 4 %. This product distribution was unchanged between seasons, despite the fact that total aerosol loading was significantly higher in the dry season and that regional and local biomass burning was a significant source of OA mass in the dry, but not wet, season. However, the OA was more oxidized in the dry season, with the median of the mean carbon oxidation state increasing from −0.45 in the wet season to −0.02 in the dry season. In the second portion of the paper, we discuss the evolution of the Manaus plume, focusing on 13 March 2014, one of the exemplary days in the wet season. On this flight, we observe a clear increase in OA concentrations in the Manaus plume relative to the background. As the plume is transported downwind and ages, we observe dynamic changes in the OA. The mean carbon oxidation state of the OA increases from −0.6 to −0.45 during the 4–5 h of photochemical aging. Hydrocarbon-like organic aerosol (HOA) mass is lost, with ΔHOA∕ΔCO values decreasing from 17.6 µg m−3 ppmv−1 over Manaus to 10.6 µg m−3 ppmv−1 95 km downwind. Loss of HOA is balanced out by formation of oxygenated organic aerosol (OOA), with ΔOOA∕ΔCO increasing from 9.2 to 23.1 µg m−3 ppmv−1. Because hydrocarbon-like organic aerosol (HOA) loss is balanced by OOA formation, we observe little change in the net Δorg∕ΔCO values; Δorg∕ΔCO averages 31 µg m−3 ppmv−1 and does not increase with aging. Analysis of the Manaus plume evolution using data from two additional flights in the wet season showed similar trends in Δorg∕ΔCO to the 13 March flight; Δorg∕ΔCO values averaged 34 µg m−3 ppmv−1 and showed little change over 4–6.5 h of aging. Our observation of constant Δorg∕ΔCO are in contrast to literature studies of the outflow of several North American cities, which report significant increases in Δorg∕ΔCO for the first day of plume aging. These observations suggest that SOA formation in the Manaus plume occurs, at least in part, by a different mechanism than observed in urban outflow plumes in most other literature studies. Constant Δorg∕ΔCO with plume aging has been observed in many biomass burning plumes, but we are unaware of reports of fresh urban emissions aging in this manner. These observations show that urban pollution emitted from Manaus in the wet season forms less particulate downwind as it ages than urban pollution emitted from North American cities.

scholarly journals Optical and Geometrical Properties of Cirrus Clouds in Amazonia Derived From 1-year of Ground-based Lidar Measurements

2016 ◽  
Author(s):  
Diego A. Gouveia ◽  
Boris Barja ◽  
Henrique M. J. Barbosa ◽  
Theotônio Pauliquevis ◽  
Paulo Artaxo
Keyword(s):  
Optical Depth ◽  
Diurnal Cycle ◽  
High Frequency ◽  
Dry Season ◽  
Cirrus Clouds ◽  
Cloud Base ◽  
Wet Season ◽  
Geometrical Properties ◽  
Lidar Ratio ◽  
The Mean

Abstract. For one year, from July 2011 to June 2012, a ground-based raman lidar provided atmospheric observations north of Manaus, Brazil, at an experimental site (2.89° S and 59.97° W) for long-term aerosol and cloud measurements. Upper tropospheric cirrus clouds were observed more frequently than previous reports in tropical regions. The frequency of occurrence was found to be as high as 82 % during the wet season and not lower than 55 % during the dry season. The diurnal cycle shows a minimum around local noon and maximum during late afternoon, associated with the diurnal cycle precipitation. Optical and geometrical characteristics of these cirrus clouds were derived. The mean values were 14.4 ± 2.0 km (top), 12.7 ± 2.3 km (base), 1.7 ± 1.5 km (thickness), and 0.36 ± 1.20 (cloud optical depth). Cirrus clouds were found at temperatures down to –90 °C and 7 % were above the tropopause base. The vertical distribution was not uniform and two cloud types were identified: (1) cloud base > 14 km and optical depth ~0.02, and (2) cloud base < 14 km and optical depth ~0.2. A third type, not previously reported, was identified during the wet season, between 16 and 18 km with optical depth ~0.005. The mean lidar ratio was 20.2 ± 7.0 sr, indicating a mixture of thick plates and long columns. However, the clouds above 14 km have a bimodal distribution during the dry season with a secondary peak at about 40 sr suggesting that thin plates are a major habit. A dependence of the lidar ratio with cloud temperature (altitude) was not found, thus indicating they are well mixed in the vertical. Cirrus clouds classified as subvisible (τ < 0.03) were 40 %, whilst 37.7 % were thin cirrus (0.03 < τ < 0.3) and 22.3 % opaque cirrus (τ > 0.3). Hence, not only does the central Amazon have a high frequency of cirrus clouds, but a large fraction of subvisible cirrus clouds as well. This high frequency of subvisible cirrus clouds may contaminate aerosol optical depth measured by sun-photometers and satellite sensors to an unknown extent.

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