scholarly journals TROPOMI reveals dry-season increase of solar-induced chlorophyll fluorescence in the Amazon forest

2019 ◽  
Vol 116 (44) ◽  
pp. 22393-22398 ◽  
Author(s):  
Russell Doughty ◽  
Philipp Köhler ◽  
Christian Frankenberg ◽  
Troy S. Magney ◽  
Xiangming Xiao ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Forest Canopy ◽  
Dry Season ◽  
Amazon Forest ◽  
Wet Season ◽  
Carbon Cycles ◽  
Sun Sensor ◽  
Sensor Geometry ◽  
Earth Observation Satellites

Photosynthesis of the Amazon rainforest plays an important role in the regional and global carbon cycles, but, despite considerable in situ and space-based observations, it has been intensely debated whether there is a dry-season increase in greenness and photosynthesis of the moist tropical Amazonian forests. Solar-induced chlorophyll fluorescence (SIF), which is emitted by chlorophyll, has a strong positive linear relationship with photosynthesis at the canopy scale. Recent advancements have allowed us to observe SIF globally with Earth observation satellites. Here we show that forest SIF did not decrease in the early dry season and increased substantially in the late dry season and early part of wet season, using SIF data from the Tropospheric Monitoring Instrument (TROPOMI), which has unprecedented spatial resolution and near-daily global coverage. Using in situ CO2 eddy flux data, we also show that cloud cover rarely affects photosynthesis at TROPOMI’s midday overpass, a time when the forest canopy is most often light-saturated. The observed dry-season increases of forest SIF are not strongly affected by sun-sensor geometry, which was attributed as creating a pseudo dry-season green-up in the surface reflectance data. Our results provide strong evidence that greenness, SIF, and photosynthesis of the tropical Amazonian forest increase during the dry season.

scholarly journals Performance of the Enhanced Vegetation Index to Detect Inner-annual Dry Season and Drought Impacts on Amazon Forest Canopies

2015 ◽  
Vol XL-7/W3 ◽  
pp. 337-344 ◽  
Author(s):  
B. Brede ◽  
J. Verbesselt ◽  
L. Dutrieux ◽  
M. Herold
Keyword(s):  
Large Scale ◽  
Vegetation Index ◽  
Standardized Precipitation Index ◽  
Dry Season ◽  
Drought Indices ◽  
Amazon Forest ◽  
Enhanced Vegetation Index ◽  
Sun Sensor ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Sensor Geometry

The Amazon rainforests represent the largest connected forested area in the tropics and play an integral role in the global carbon cycle. In the last years the discussion about their phenology and response to drought has intensified. A recent study argued that seasonality in greenness expressed as Enhanced Vegetation Index (EVI) is an artifact of variations in sun-sensor geometry throughout the year. We aimed to reproduce these results with the Moderate-Resolution Imaging Spectroradiometer (MODIS) MCD43 product suite, which allows modeling the Bidirectional Reflectance Distribution Function (BRDF) and keeping sun-sensor geometry constant. The derived BRDF-adjusted EVI was spatially aggregated over large areas of central Amazon forests. The resulting time series of EVI spanning the 2000-2013 period contained distinct seasonal patterns with peak values at the onset of the dry season, but also followed the same pattern of sun geometry expressed as Solar Zenith Angle (SZA). Additionally, we assessed EVI’s sensitivity to precipitation anomalies. For that we compared BRDF-adjusted EVI dry season anomalies to two drought indices (Maximum Cumulative Water Deficit, Standardized Precipitation Index). This analysis covered the whole of Amazonia and data from the years 2000 to 2013. The results showed no meaningful connection between EVI anomalies and drought. This is in contrast to other studies that investigate the drought impact on EVI and forest photosynthetic capacity. The results from both sub-analyses question the predictive power of EVI for large scale assessments of forest ecosystem functioning in Amazonia. Based on the presented results, we recommend a careful evaluation of the EVI for applications in tropical forests, including rigorous validation supported by ground plots.

scholarly journals Diurnal, Seasonal and Annual Variation of Microwave Radio Refractivity Gradient over Akure, South West Nigeria

2019 ◽  
pp. 1-11
Author(s):  
Adekunle Titus Adediji ◽  
Joseph Babatunde Dada ◽  
Moses Oludare Ajewole
Keyword(s):  
Rainy Season ◽  
Annual Variation ◽  
Ground Surface ◽  
Local Effect ◽  
Dry Season ◽  
Radio Link ◽  
Wet Season ◽  
Annual Variations ◽  
Microwave Radio

In this study, four years in-situ measurements of atmospheric parameters (pressure, temperature and relative humidity) were carried out. The measurement was by placing an automatic weather station at five different heights: ground surface, 50, 100, 150 and 200 m respectively on a 220 m Nigeria Television Authority TV tower in Akure, South Western Nigeria. The four years Data collected (January 2007 to December 2009 and January to December 2011) were used to compute radio refractivity and its gradient. The local effect of a location/ region cannot but looked into when designing effective radio link, hence the diurnal, seasonal and annual variations of the radio refractivity gradient were studied. Results showed that refractivity gradient steadily increases inthe hour of 8:30 and 9:30 to 18:00 during dry season throughout the years investigated, and decreases two hours in the rainy season than the dry season. The record shows that at 50 m altitude, the maximum and minimum values are 158 N-unit/km around 14:30 and - 286 N-unit/km around 13:30 to 14:00 hrs, LT during the dry and rainy season respectively. Seasonally, refractivity gradient is steeper with greater variability in the dry season months than in the wet season months.

scholarly journals Biomass-burning and urban emission impacts in the Andes Cordillera region based on in-situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)

2019 ◽  
Author(s):  
Chauvigné Aurélien ◽  
Diego Aliaga ◽  
Marcos Andrade ◽  
Patrick Ginot ◽  
Radovan Krejci ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Particle ◽  
Biomass Burning ◽  
Dry Season ◽  
Wet Season ◽  
Stable Layer ◽  
La Paz ◽  
Extinction Coefficients ◽  
El Alto

Abstract. We present the variability of aerosol particle optical properties measured at the global Atmosphere Watch (GAW) station Chacaltaya (5240 m a.s.l.). The in-situ mountain site is ideally located to study regional impacts of the densely populated urban area of La Paz/El Alto, and the intensive activity in the Amazonian basin. Four year measurements allow to study aerosol particle properties for distinct atmospheric conditions as stable and turbulent layers, different airmass origins, as well as for wet and dry seasons, including biomass-burning influenced periods. The absorption, scattering and extinction coefficients (median annual values of 0.74, 12.14 and 12.96 Mm−1 respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94 and 8.68 Mm−1 respectively) and higher values during the dry season (0.80, 11.23 and 14.51 Mm−1 respectively). These parameters also show a pronounced diurnal variation (maximum during daytime, minimum during night-time, as a result of the dynamic and convective effects of leading to lower atmospheric layers reaching the site during daytime. Retrieved intensive optical properties are significantly different from one season to the other, showing the influence of different sources of aerosols according to the season. Both intensive and extensive optical properties of aerosols were found to be different among the different atmospheric layers. The particle light absorption, scattering and extinction coefficients are in average 1.94, 1.49 and 1.55 times higher, respectively, in the turbulent layer compared to the stable layer. We observe that the difference is highest during the wet season and lowest during the dry season. Using wavelength dependence of aerosol particle optical properties, we discriminated contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass-burning and urban transport or industries) emissions according to seasons and tropospheric layers. The main sources influencing measurements at CHC are arising from the urban area of La Paz/El Alto, and regional biomass-burning from the Amazonian basin. Results show a 28 % to 80 % increase of the extinction coefficients during the biomass-burning season with respect to the dry season, which is observed in both tropospheric layers. From this analyse, long-term observations at CHC provides the first direct evidence of the impact of emissions in the Amazonian basin on atmospheric optical properties far away from their sources, all the way to the stable layer.

Observations on the Biting-habits of some Tabanidae in Uganda, with special Reference to arboreal and nocturnal Activity

1950 ◽  
Vol 41 (1) ◽  
pp. 209-221 ◽  
Author(s):  
A. J. Haddow ◽  
J. D. Gillett ◽  
A. F. Mahaffy ◽  
R. B. Highton
Keyword(s):  
Special Reference ◽  
Yellow Fever ◽  
Forest Canopy ◽  
Dry Season ◽  
Forest Trees ◽  
Close Correspondence ◽  
Nocturnal Activity ◽  
Wet Season ◽  
Natural Hosts ◽  
Biting Behaviour

In a search for the forest vector of yellow fever, catches of biting Diptera have been made by various methods in forest trees in Bwamba County, Uganda. The work here reported concerns Tabanids taken in catches made during the period 1944–45.Three species of Tabanids have been taken in trees during these catches, and one of these, Chrysops centurionis, has proved to be mainly arboreal.Observations on C. centurionis have shown that its main biting-activity begins just before sunset and reaches a peak during the hour after sunset. Thereafter the numbers taken diminish rapidly, but some activity continues throughout the night.In the wet-season catches, this species was most prevalent in the forest canopy at heights of 50 to 60 feet above ground. In the dry season the most favourable level was lower, at 20 to 30 feet above ground.It is suggested that monkeys are the natural hosts of C. centurionis, and that C. centurionis may be the vector of filarial infections among wild monkeys.It is shown that there is a very close correspondence between the biting-behaviour of C. centurionis and that of the mosquito, A ëdes africanus.Evidence of nocturnal activity has now been obtained in the case of one species of Tdbanus, three species of Haematopota and two species of Chrysops. It is suggested that there may be some connection between the remarkable eye colours of Tabanids and crepuscular or nocturnal activity.Records of other Bwamba Tabanids are given.

scholarly journals Global GOSAT, OCO-2 and OCO-3 Solar Induced Chlorophyll Fluorescence Datasets

2021 ◽  
Author(s):  
Russell Doughty ◽  
Thomas Kurosu ◽  
Nicholas Parazoo ◽  
Philipp Köhler ◽  
Yujie Wang ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Earth Observation ◽  
Background Information ◽  
Sun Sensor ◽  
Global Target ◽  
Target Sites ◽  
Data Products ◽  
Sensor Geometry ◽  
Indirect Relationship ◽  
Level 2

Abstract. The retrieval of solar induced chlorophyll fluorescence (SIF) from space is a relatively new advance in Earth observation science, having only become feasible within the last decade. Interest in SIF data has grown exponentially, and the retrieval of SIF and the provision of SIF data products has become an important and formal component of spaceborne Earth observation missions. Here, we describe the global Level 2 SIF Lite data products for the Greenhouse Gases Observing Satellite (GOSAT), the Orbiting Carbon Observatory-2 (OCO-2), and OCO-3 platforms, which are provided for each platform in daily netCDF files. We also outline the methods used to retrieve SIF and estimate uncertainty, describe all the data fields, and provide users the background information necessary for the proper use and interpretation of the data, such as considerations of retrieval noise, sun-sensor geometry, the indirect relationship between SIF and photosynthesis, and differences among the three platforms and their respective data products. OCO-2 and OCO-3 have the highest spatial resolution spaceborne SIF retrievals to date, and the target and snapshot area mode observation modes of OCO-2 and OCO-3 are unique. These modes provide hundreds to thousands of SIF retrievals at biologically diverse global target sites during a single overpass, and provide an opportunity to better inform our understanding of canopy-scale vegetation SIF emission across biomes.

scholarly journals Measurements of soil respiration and simple models dependent on moisture and temperature for an Amazonian southwest tropical forest

2009 ◽  
Vol 6 (3) ◽  
pp. 6147-6177 ◽  
Author(s):  
F. B. Zanchi ◽  
H. R. da Rocha ◽  
H. C. de Freitas ◽  
B. Kruijt ◽  
M. J. Waterloo ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Soil Respiration ◽  
Soil Temperature ◽  
Field Measurements ◽  
Dry Season ◽  
Wet Season ◽  
Hourly Data ◽  
Fresh Litter ◽  
Favorable Conditions

Abstract. Soil respiration plays a significant role in the carbon cycle of Amazonian tropical forests, although in situ measurements have only been poorly reported and the dependence of soil moisture and soil temperature also weakly understood. This work investigates the temporal variability of soil respiration using field measurements, which also included soil moisture, soil temperature and litterfall, from April 2003 to January 2004, in a southwest Brazilian tropical rainforest near Ji-Paraná, Rondônia. The experimental design deployed five automatic (static, semi-opened) soil chambers connected to an infra-red CO2 gas analyzer. The mean half-hourly soil respiration showed a large scattering from 0.6 to 18.9 μmol CO2 m−2 s−1 and the average was 8.0±3.4 μmol CO2 m−2 s−1. Soil respiration varied seasonally, being lower in the dry season and higher in the wet season, which generally responded positively to the variation of soil moisture and temperature year round. The peak was reached in the dry-to-wet season transition (September), this coincided with increasing sunlight, evapotranspiration and ecosystem productivity. Litterfall processes contributed to meet very favorable conditions for biomass decomposition in early wet season, especially the fresh litter on the forest floor accumulated during the dry season. We attempted to fit three models with the data: the exponential Q10 model, the Reichstein model, and the log-soil moisture model. The models do not contradict the scattering of observations, but poorly explain the variance of the half-hourly data, which is improved when the lag-time days averaging is longer. The observations suggested an optimum range of soil moisture, between 0.115

scholarly journals On the impact of canopy model complexity on simulated carbon, water, and solar-induced chlorophyll fluorescence fluxes

2021 ◽  
Author(s):  
Yujie Wang ◽  
Christian Frankenberg
Keyword(s):  
Chlorophyll Fluorescence ◽  
Land Surface ◽  
Climate Modeling ◽  
Global Scale ◽  
Model Complexity ◽  
Transfer Scheme ◽  
Sun Sensor ◽  
Sensor Geometry ◽  
The Impact ◽  
Canopy Model

Abstract. Lack of direct carbon, water, and energy flux observations at global scales makes it difficult to calibrate land surface models (LSMs). The increasing number of remote sensing based products provide an alternative way to verify or constrain land models given its global coverage and satisfactory spatial and temporal resolutions. However, these products and LSMs often differ in their assumptions and model setups, for example, the canopy model complexity. The disagreements hamper the fusion of global scale datasets with LSMs. To evaluate how much the canopy complexity affects predicted canopy fluxes, we simulated and compared the carbon, water, and solar-induced chlorophyll fluorescence (SIF) fluxes using five different canopy complexity setups from a one-layered big-leaf canopy to a multi-layered canopy with leaf angular distributions. We modeled the canopy fluxes using a recently developed Land model by the Climate Modeling Alliance. Our model results suggested that (1) when using the same model inputs, model predicted carbon, water, and SIF fluxes were all higher for simpler canopy setups; (2) when accounting for vertical photosynthetic capacity heterogeneity, differences among canopy complexity levels increased compared to the scenario of a uniform canopy; (3) SIF fluxes modeled with different canopy complexity levels changed with sun-sensor geometry. Given the different modeled canopy fluxes with different canopy complexities, we recommend (1) not misusing parameters inverted with different canopy complexities or assumptions to avoid biases in model outputs, and (2) using complex canopy model with angular distribution and hyperspectral radiation transfer scheme when linking land processes to remotely sensed spectra.

scholarly journals Total OH reactivity over the Amazon rainforest: variability with temperature, wind, rain, altitude, time of day, season, and an overall budget closure

2021 ◽  
Vol 21 (8) ◽  
pp. 6231-6256
Author(s):  
Eva Y. Pfannerstill ◽  
Nina G. Reijrink ◽  
Achim Edtbauer ◽  
Akima Ringsdorf ◽  
Nora Zannoni ◽  
...  
Keyword(s):  
Tropical Forests ◽  
Time Of Day ◽  
Green Leaf Volatiles ◽  
Dry Season ◽  
Amazon Forest ◽  
Wet Season ◽  
Leaf Volatiles ◽  
Transition Season ◽  
Wide Range ◽  
Volatile Organic

Abstract. The tropical forests are Earth's largest source of biogenic volatile organic compounds (BVOCs) and thus also the largest atmospheric sink region for the hydroxyl radical (OH). However, the OH sink above tropical forests is poorly understood, as past studies have revealed large unattributed fractions of total OH reactivity. We present the first total OH reactivity and volatile organic compound (VOC) measurements made at the Amazon Tall Tower Observatory (ATTO) at 80, 150, and 320 m above ground level, covering two dry seasons, one wet season, and one transition season in 2018–2019. By considering a wide range of previously unaccounted for VOCs, which we identified by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), the unattributed fraction was with an overall average of 19 % within the measurement uncertainty of ∼ 35 %. In terms of seasonal average OH reactivity, isoprene accounted for 23 %–43 % of the total and oxygenated VOCs (OVOCs) for 22 %–40 %, while monoterpenes, sesquiterpenes, and green leaf volatiles combined were responsible for 9 %–14 %. These findings show that OVOCs were until now an underestimated contributor to the OH sink above the Amazon forest. By day, total OH reactivity decreased towards higher altitudes with strongest vertical gradients observed around noon during the dry season (−0.026 s−1 m−1), while the gradient was inverted at night. Seasonal differences in total OH reactivity were observed, with the lowest daytime average and standard deviation of 19.9 ± 6.2 s−1 during a wet–dry transition season with frequent precipitation; 23.7 ± 6.5 s−1 during the wet season; and the highest average OH reactivities during two dry-season observation periods with 28.1 ± 7.9 s−1 and 29.1 ± 10.8 s−1, respectively. The effects of different environmental parameters on the OH sink were investigated, and quantified, where possible. Precipitation caused short-term spikes in total OH reactivity, which were followed by below-normal OH reactivity for several hours. Biomass burning increased total OH reactivity by 2.7 to 9.5 s−1. We present a temperature-dependent parameterization of OH reactivity that could be applied in future models of the OH sink to further reduce our knowledge gaps in tropical-forest OH chemistry.

scholarly journals Summertime Moisture Transport to the Southern South American Altiplano: Constraints from In Situ Measurements of Water Vapor Isotopic Composition

2015 ◽  
Vol 28 (7) ◽  
pp. 2635-2649 ◽  
Author(s):  
Joseph Galewsky ◽  
Kimberly Samuels-Crow
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
Austral Summer ◽  
Dry Season ◽  
In Situ Measurements ◽  
South American ◽  
Moist Air ◽  
Wet Season ◽  
Rayleigh Distillation

Abstract Austral summer transport of water vapor to the southern South American Altiplano is investigated using in situ measurements of water vapor isotopic composition collected from 1 November 2012 to 10 February 2013 on the Chajnantor Plateau in the Chilean Andes. Onset of the wet season in December was associated with an increase in mixing ratios from an average of 1500 ppmv during the winter dry season to 5400 ppmv in early December. Water vapor isotopes δD and δ18O increased from dry season averages of −235‰ and −31‰, respectively, to wet season averages of −142‰ and −17‰, reaching as high as −70‰ and −17‰, respectively. The highest water vapor δ values were close to those measured in coastal settings, suggesting little condensation during transport to the site. About 5% of the wet season data have δ values that are lower than expected for Rayleigh distillation and are associated with high relative humidity (>75%), easterly winds, and periods of low outgoing longwave radiation over the Altiplano, consistent with moistening by deep convection. The remainder of the data have δ values that are greater than expected for Rayleigh distillation, up to 250‰ above the Rayleigh curve. These data are consistent with mixing between very dry air and moist air from the boundary layer. The data show intraseasonal variability coherently linked to the position of the Bolivian high, with moist air associated with a southward displacement in the Bolivian high. The humidity over the southern Altiplano during the wet season reflects a balance among advective drying, advective moistening with little condensation, and convective moistening.

scholarly journals On the impact of canopy model complexity on simulated carbon, water, and solar-induced chlorophyll fluorescence fluxes

2022 ◽  
Vol 19 (1) ◽  
pp. 29-45
Author(s):  
Yujie Wang ◽  
Christian Frankenberg
Keyword(s):  
Chlorophyll Fluorescence ◽  
Land Surface ◽  
Climate Modeling ◽  
Global Scale ◽  
Model Complexity ◽  
Transfer Scheme ◽  
Sun Sensor ◽  
Sensor Geometry ◽  
The Impact ◽  
Canopy Model

Abstract. Lack of direct carbon, water, and energy flux observations at global scales makes it difficult to calibrate land surface models (LSMs). The increasing number of remote-sensing-based products provide an alternative way to verify or constrain land models given their global coverage and satisfactory spatial and temporal resolutions. However, these products and LSMs often differ in their assumptions and model setups, for example, the canopy model complexity. The disagreements hamper the fusion of global-scale datasets with LSMs. To evaluate how much the canopy complexity affects predicted canopy fluxes, we simulated and compared the carbon, water, and solar-induced chlorophyll fluorescence (SIF) fluxes using five different canopy complexity setups from a one-layered canopy to a multi-layered canopy with leaf angular distributions. We modeled the canopy fluxes using the recently developed land model by the Climate Modeling Alliance, CliMA Land. Our model results suggested that (1) when using the same model inputs, model-predicted carbon, water, and SIF fluxes were all higher for simpler canopy setups; (2) when accounting for vertical photosynthetic capacity heterogeneity, differences between canopy complexity levels increased compared to the scenario of a uniform canopy; and (3) SIF fluxes modeled with different canopy complexity levels changed with sun-sensor geometry. Given the different modeled canopy fluxes with different canopy complexities, we recommend (1) not misusing parameters inverted with different canopy complexities or assumptions to avoid biases in model outputs and (2) using a complex canopy model with angular distribution and a hyperspectral radiation transfer scheme when linking land processes to remotely sensed spectra.

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