Boon Ning Chew

Daytime Top-of-the-Atmosphere Cirrus Cloud Radiative Forcing Properties at Singapore

AbstractDaytime top-of-the-atmosphere (TOA) cirrus cloud radiative forcing (CRF) is estimated for cirrus clouds observed in ground-based lidar observations at Singapore in 2010 and 2011. Estimates are derived both over land and water to simulate conditions over the broader Maritime Continent archipelago of Southeast Asia. Based on bookend constraints of the lidar extinction-to-backscatter ratio (20 and 30 sr), used to solve extinction and initialize corresponding radiative transfer model simulations, relative daytime TOA CRF is estimated at 2.858–3.370 W m−2 in 2010 (both 20 and 30 sr, respectively) and 3.078–3.329 W m−2 in 2011 and over water between −0.094 and 0.541 W m−2 in 2010 and −0.598 and 0.433 W m−2 in 2011 (both 30 and 20 sr, respectively). After normalizing these estimates for an approximately 80% local satellite-estimated cirrus cloud occurrence rate, they reduce in absolute daytime terms to 2.198–2.592 W m−2 in 2010 and 2.368–2.561 W m−2 in 2011 over land and −0.072–0.416 W m−2 in 2010 and −0...

Applying Advanced Ground-Based Remote Sensing in the Southeast Asian Maritime Continent to Characterize Regional Proficiencies in Smoke Transport Modeling

ABSTRACTThis work describes some of the most extensive ground-based observations of the aerosol profile collected in Southeast Asia to date, highlighting the challenges in simulating these observations with a mesoscale perspective. An 84-h WRF Model coupled with chemistry (WRF-Chem) mesoscale simulation of smoke particle transport at Kuching, Malaysia, in the southern Maritime Continent of Southeast Asia is evaluated relative to a unique collection of continuous ground-based lidar, sun photometer, and 4-h radiosonde profiling. The period was marked by relatively dry conditions, allowing smoke layers transported to the site unperturbed by wet deposition to be common regionally. The model depiction is reasonable overall. Core thermodynamics, including land/sea-breeze structure, are well resolved. Total model smoke extinction and, by proxy, mass concentration are low relative to observation. Smoke emissions source products are likely low because of undersampling of fires in infrared sun-synchronous satellite...

High Spectral Resolution Lidar and MPLNET Micro Pulse Lidar aerosol optical property retrieval intercomparison during the 2012 7-SEAS field campaign at Singapore

From August 2012 to February 2013 a High Resolution Spectral Lidar (HSRL; 532 nm) was deployed at that National University of Singapore near a NASA Micro Pulse Lidar NETwork (MPLNET; 527 nm) site. A primary objective of the MPLNET lidar project is the production and dissemination of reliable Level 1 measurements and Level 2 retrieval products. This paper characterizes and quantifies error in Level 2 aerosol optical property retrievals conducted through inversion techniques that derive backscattering and extinction coefficients from MPLNET elastic single-wavelength datasets. MPLNET Level 2 retrievals for aerosol optical depth and extinction/backscatter coefficient profiles are compared with corresponding HSRL datasets, for which the instrument collects direct measurements of each using a unique optical configuration that segregates aerosol and cloud backscattered signal from molecular signal. The intercomparison is performed, and error matrices reported, for lower (0-5km) and the upper (>5km) troposphere, respectively, to distinguish uncertainties observed within and above the MPLNET instrument optical overlap regime.

Haze in Singapore n Source Attribution of Biomass Burning from Southeast Asia

This paper presents a study of haze in Singapore caused by biomass burning in Southeast Asia over the six year period from 2010 to 2015, using the Lagrangian dispersion model, NAME. The major contributing source regions are shown to be Riau, Peninsular Malaysia, South Sumatra, and Central and West Kalimantan. However, we see differences in haze concentrations and variation in the relative contributions from the various source regions between monitoring stations across Singapore, as well as on an inter-annual timescale. These results challenge 5 the current popular assumption that haze in Singapore is dominated by emissions/burning from only Indonesia. It is shown that Peninsular Malaysia is a large source for the Maritime Continent off-season biomass burning impact on Singapore. As should be expected, the relatively stronger Southeast monsoonal winds that coincide with increased biomass burning activities in the Maritime Continent create the main haze season from August to October (ASO), which brings particulate matter from varying source regions to Singapore. Five regions dominate as the source of pollution during recent haze seasons. 10 In contrast, off-season haze episodes in Singapore are characterised by unusual weather conditions, ideal for biomass burning, and emissions dominated by a single source region (for each event). The two most recent off-season haze events in mid-2013 and early-2014 have different source regions, which differ to the major contributing source regions for the haze season. Haze in Singapore varies across year, season, and location; it is influenced by local and regional weather, climate, and regional burning. The study shows that even across small scales, such as in Singapore, variation in local meteorology can 15 impact concentrations of particulate matter significantly, and emphasises the importance of the scale of modelling both spatially and temporally.

First results from AERONET mini-dragon photometer network set-up at Singapore

We report our first photometric measurements of aerosol optical depth from AERONETs mini-DRAGON sites at Singapore performed over the months of August and September 2012. Multi-spectral measurements of aerosol optical depth provide essential spectral information to obtain and/or retrieve the so-called Angstrom exponent number which is an essential parameter for inferring aerosol particle size regime. Based on the range of variability of Angstrom exponent number and aerosol optical depth, various aerosol types present in the local environment, can be identified. Special emphasis is placed on detecting the possible presence of external sources of aerosols such as from trans-boundary smoke originating from regional biomass burning episodes which is prevalent during this time of the year.

Radiative impact of biomass burning events: the October 2010 smoke episode in South-East Asia

Over the past two decades, the Asia and South-Asia region has experienced a dramatic economic, industrial and population grow. Big cities are becoming large emission sources of anthropogenic aerosols resulting from the incessant industrial activity. In rural areas, clearance of large forested areas, via the method of burning, has resulted in severe smoke emission episodes during the 1996-2006 decade and has become an annual phenomenon specially in the South-East-Asia region. Large emission episodes can occur during periods of severe draught and exacerbated by the inter- annual El Ninõ events. Depending on weather patterns, smoke events can evolve into a persistent trans-boundary smoke with aerosol concentrations high enough to significantly reduce visibility and become a health hazard for local populations. During the month of October 2010, elevated levels of fire activity was detected by remote sensing satellites as well as by local in-situ measurements of fine particulate matter. In this work, we investigate the radiative impact of this smoke episode by firstly, analyzing the physical and optical properties of smoke particles with the aid of passive (Sun-photometer, AERONET), active and in-situ sampling of fine particulate (PM2.5) at our Singapore receptor site. Secondly, inversions of particle size distribution as well as single scattering albedo were used to evaluate the radiative impact of this biomass burning episode.