Satellite estimation of photosynthetically active radiation in Southeast Asia: Impacts of smoke and cloud cover

Abstract

.[1] Since large-scale variations in photosynthetically active radiation (PAR) influence the terrestrial carbon sources and sinks through the plant photosynthesis variations, large-scale evaluation of PAR is required. In the present study a simple PAR estimation model was developed for Southeast Asia, where large-scale forest fires occurred during El Niño years. The model considered the smoke aerosol released by forest fires using satellitebased smoke detection methods. A comparison study with ground-based solar radiation data for Malaysia and Thailand indicated that the current model could estimate monthly PAR with 10% (root-mean-square) accuracy and would successfully trace the seasonal and year-to-year variations in PAR, including the forest fire periods. During the peaksmoke month in Indonesia, September 1997, the reduction of PAR by smoke reached 63-75% in the center of the Kalimantan and Sumatra Islands. From the analyses of the smoke and cloud cover impacts on PAR in 1997-1999, annual PAR variations were found to be mostly regulated by smoke variations on the Malay Peninsula, Sumatra, and Kalimantan Islands and cloud cover variations on the Indo-China Peninsula. Thus annual variations in PAR changed with location. These variations did not simply correlate with year-to-year variations in cloud cover associated with the El Niño and La Niña cycle, but exhibited more complicated spatial variations due to the existence of smoke in Southeast Asia.

Potential impacts of aerosol–land–atmosphere interactions on the Indian monsoonal rainfall characteristics

“…For example, biomass burning as a common practice of land clearing for agriculture is the dominant source of tropospheric aerosols in tropical areas. These aerosols can substantially modulate surface radiative and moisture conditions through their direct and indirect effects (Kobayashi et al 2004). Because tropical rainforests generally have higher leaf area indices than forests in other climate zones, such as temperate forests, aerosols in moist tropical areas are expected to exert a stronger control on vegetation activities through the diffuse radiation effect than those reported for temperate or boreal forests.…”

Modeling and analysis of the spatiotemporal variations of photosynthetically active radiation in China during 1961–2012

“…PAR has to be estimated through either empirical/semiphysical methods or remote sensing techniques (e.g. [24,1]), for example, Van Laake and Sanchez-Azofeifa [37] proposed a method (PARcalc) for mapping instantaneous PAR from MODIS data based on radiative transfer equations, they further calculated the daily integrated PAR in Costa Rica and the average errors were 5-8% [38,27] mapped the incident PAR from MODIS data over China by matching the computed TOA (top of atmosphere) reflectance from a look-up table with the TOA values from the satellite observation; Janjai and Wattan [22] developed a model for estimating PAR from geostationary satellite in a tropical environment (Thailand) and the monthly average hourly root mean square error (RMSE) was about 9.8%; Leuchner et al [25] analyzed the spatial variability of PAR in European beech and Norway spruce; Qin et al [31] estimated the daily mean PAR at seven widely distributed Surface Radiation Budget Network (SUR-FRAD) stations around the world using relative sunshine data, and the RMSE was ranging from 6.03 to 6.83 W m À 2 ; Mizoguchi et al [30] estimated PAR using general meteorological elements at five sites in Japan and found that the RMSE was smaller than 5.2%. However, it was reported that many of many studies were focused on clear sky conditions (e.g.…”

Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

“…Direct radiative forcing: Through scattering and absorption of solar and terrestrial radiation, aerosol particles play a primary role in the clear sky (and, as we suggest later, in some cases in the cloudy sky) radiative budget (Davison et al, 2004;Rajeev et al, 2008;Feng and Christopher, 2013-this issue). Perturbations to photosynthetic active radiation at the surface by regional smoke can be significant (Kobayashi et al, 2004). Meteorology, semi-direct, and indirect forcing: Through perturbation of the surface radiation budgets, aerosol particles impact sensible and latent heat fluxes (Bala Subrahamanyam et al, 2011).…”