scholarly journals Validation of MODIS derived aerosol optical depth and an investigation on aerosol transport over the South East Arabian Sea during ARMEX-II

2009 ◽  
Vol 27 (6) ◽  
pp. 2285-2296 ◽  
Author(s):  
M. Aloysius ◽  
M. Mohan ◽  
S. Suresh Babu ◽  
K. Parameswaran ◽  
K. Krishna Moorthy
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mass Concentration ◽  
Arabian Sea ◽  
Second Phase ◽  
The South ◽  
Monsoon Period ◽  
Lower Altitude ◽  
The North ◽  
Coarse Mode

Abstract. The influence of wind and humidity on aerosol optical depth (AOD) over the Arabian sea is being investigated using MODIS (Moderate Resolution Imaging Spectroradiometer) Level 3 (Collection-5) and NCEP (National Centres for Environmental Prediction) reanalysis data for the second phase of the Arabian Sea Monsoon Experiment (ARMEX-II) over the South East Arabian Sea (SEAS) in the pre-monsoon period (14 March–10 April 2003). In order to qualify MODIS data for this study, MODIS aerosol parameters were first compared with ship borne Microtops measurements. This showed correlations 0.96–0.97 in the case of spectral AODs and a correlation 0.72 for the angstrom exponents. The daily AOD data from MODIS and winds from NCEP reveal that the ship observed episodic enhancement and decay of AOD at the TSL (Time Series Location) during 23 March–6 April 2003 was caused by the southward drift of an aerosol pocket driven by an intensification and reduction of surface pressure in the North Western Arabian Sea with a low altitude convergence prevailing over SEAS. The AOD increase coincided with a decrease in the Angstrom exponent and the fine mode fraction suggesting the pocket being dominated by coarse mode particles. A partial correlation analysis reveals that the lower altitude wind convergence is the most influential atmospheric variable in modulating AOD over the ARMEX-II domain during the TSL period. However, surface winds at a distant zone in the north/north west upwind direction also had a moderate influence, though with a lag of two days. But this effect was minor since the winds were not strong enough to produce marine aerosols matching with the high AODs over the ARMEX-II domain. These findings and the similarity between MODIS column mass concentration and the ship borne QCM (Quartz Crystal Microbalance) measured coarse mode mass concentration, suggest that the aerosol pocket was mostly composed of coarse mode mineral dust in the lower atmospheric altitudes transported from the Arabian deserts.

scholarly journals Microseisms associated with disturbed weather in the Indian seas

1930 ◽  
Vol 229 (670-680) ◽  
pp. 287-328 ◽  
Keyword(s):  
North Atlantic ◽  
Arabian Sea ◽  
The State ◽  
The South ◽  
Monsoon Period ◽  
The North ◽  
Steady Vibrations ◽  
South West Monsoon ◽  
Seismic Records ◽  
West Monsoon

Seismologists have often noted the appearance of pronounced microseisms in seismic records when the weather has been disturbed over a neighbouring sea. For instance, the late Dr. KLOTZ suggested a relationship between disturbed weather in the north Atlantic and the largest microseismic movements at Ottawa. Dr. HARRISON, writing in ' Nature,’ November 1, 1924, in continuation of a note* by the present writer, pointed out that well-marked microseisms in the Omori charts at Calcutta invariably confirmed other evidence in the case of the early stages of dangerous cyclones, and were sometimes noticed when the storm centre was so much as 1000 miles south of Calcutta. He did not, however, recall any instance in which microseisms were associated with ordinary rough weather or with an advance of the monsoon. On the other hand, “ investigation at Eskdalemuir of the possible connection between microseismical amplitude and the state of the sea at different points of the British coasts have yielded results of an inconclusive kind. For example, the correlation between the state of the sea and the Microseismic movements of a type, which were quite characteristic of the south-west monsoon period, made their first appearance in the seismograms generally in May with the advance of the monsoon in the south-east Arabian Sea, becoming more and more pronounced as the monsoon currents approached Bombay. They became less marked or disappeared during a temporary break in the monsoon and reappeared with the strengthening of the currents. They were more or less steady vibrations having periods ranging from 4 to 10 seconds.

scholarly journals Aerosol optical properties at Lampedusa (Central Mediterranean). 1. Influence of transport and identification of different aerosol types

2006 ◽  
Vol 6 (3) ◽  
pp. 697-713 ◽  
Author(s):  
G. Pace ◽  
A. di Sarra ◽  
D. Meloni ◽  
S. Piacentino ◽  
P. Chamard
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Central Mediterranean ◽  
Desert Dust ◽  
Central Eastern Europe ◽  
Angstrom Exponent ◽  
The North ◽  
Ångström Exponent ◽  
Summer Maximum ◽  
Ångstrom Exponent

Abstract. Aerosol optical depth and Ångström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001–September 2003. The average aerosol optical depth at 495.7 nm, τ, is 0.24±0.14; the average Ångström exponent, α, is 0.86±0.63. The observed values of τ range from 0.03 to 1.13, and the values of α vary from −0.32 to 2.05, indicating a large variability in aerosol content and size. In cloud-free conditions, 36% of the airmasses come from Africa, 25% from Central-Eastern Europe, and 19% from Western France, Spain and the North Atlantic. In summer, 42% of the airmasses is of African origin. In almost all cases African aerosols display high values of τ and low values of α, typical of Saharan dust (average values of τ and α are 0.36 and 0.42, respectively). Particles originating from Central-Eastern Europe show relatively large average values of τ and α (0.23 and 1.5, respectively), while particles from Western France, Spain and the North Atlantic show the lowest average values of τ (0.15), and relatively small values of α (0.92). Intermediate values of α are often connected with relatively fast changes of the airmass originating sector, suggesting the contemporary presence of different types of particles in the air column. Clean marine conditions are rare at Lampedusa, and are generally associated with subsidence of the airmasses reaching the island. Average values of τ and α for clean marine conditions are 0.11 and 0.86, respectively. The largest values of α (about 2) were observed in August 2003, when large scale forest fires in Southern Europe produced consistent amounts of fine combustion particles, that were transported to the Central Mediterranean by a persistent high pressure system over Central Europe. Smoke particles in some cases mix with desert dust, producing intermediate values of α. The seasonal distribution of the meteorological patterns over the Mediterranean, the efficiency of the aerosol production mechanisms, and the variability of the particles' residence time produce a distinct seasonal cycle of aerosol optical depths and Ångström exponent values. Particles originating from all sectors show a summer maximum in aerosol optical depth. The summer increase in optical depth for European aerosols is linked with an increment in the values of α, that indicates an enhancement in the number of fine particles. The summer maximum of τ for African particles is associated with a weak reduction in the Ångström exponent, suggesting an increase in the total number of particles and a relatively more intense transport of large particles. The observations were classified according to the aerosol optical properties, and two main classes have been identified: desert dust and biomass burning/urban-industrial aerosols. Values of τ and α averaged over the whole observing period are 0.37 and 0.15 for desert dust, and 0.27 and 1.77 for urban-industrial/biomass burning aerosols.

scholarly journals Comparison of MODIS and AERONET derived aerosol optical depth over the Ganga Basin, India

2005 ◽  
Vol 23 (4) ◽  
pp. 1093-1101 ◽  
Author(s):  
S. N. Tripathi ◽  
Sagnik Dey ◽  
A. Chandel ◽  
S. Srivastava ◽  
Ramesh P. Singh ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Time Window ◽  
Absolute Error ◽  
Absolute Difference ◽  
Ganga Basin ◽  
Monsoon Period ◽  
Post Monsoon ◽  
Dust Loading ◽  
The Absolute

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) onboard EOS Terra measures global aerosol optical depth and optical properties since 2000. MODIS aerosol products are freely available and are being used for numerous studies. In this paper, we present a comparison of aerosol optical depth (AOD) retrieved from MODIS with Aerosol Robotic Network (AERONET) data for the year 2004 over Kanpur, an industrial city lying in the Ganga Basin in the northern part of India. AOD retrieved from MODIS (τaMODIS) at 0.55µm wavelength has been compared with the AERONET derived AOD (τaAERONET), within an optimum space-time window. Although the correlation between τaMODIS and τaAERONET during the post-monsoon and winter seasons (R2~0.71) is almost equal to that during the pre-monsoon and monsoon seasons (R2~0.72), MODIS is found to overestimate AOD during the pre-monsoon and monsoon period (characterized by severe dust loading) and underestimate during the post-monsoon and winter seasons. The absolute difference between τaMODIS and τaAERONET is found to be low (0.12±0.11) during the non-dust loading season and much higher (0.4±0.2) during dust-loading seasons. The absolute error in τaMODIS is found to be about ~25% of the absolute values of τaMODIS. Our comparison shows the importance of modifying the existing MODIS algorithm during the dust-loading seasons, especially in the Ganga Basin in northern part of India.

Relationship between MODIS based Aerosol Optical Depth and PM10 over Croatia

2014 ◽  
Vol 6 (1) ◽  
Author(s):  
Sanja Grgurić ◽  
Josip Križan ◽  
Goran Gašparac ◽  
Oleg Antonić ◽  
Zdravko Špirić ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mass Concentration ◽  
Meteorological Data ◽  
Neural Network Approach ◽  
Data Set ◽  
Independent Variables ◽  
Data Variability ◽  
Modis Aod ◽  
The Relationship

AbstractThis study analyzes the relationship between Aerosol Optical Depth (AOD) obtained from Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based PM10 mass concentration distribution over a period of 5 years (2008–2012), and investigates the applicability of satellite AOD data for ground PM10 mapping for the Croatian territory. Many studies have shown that satellite AOD data are correlated to ground-based PM mass concentration. However, the relationship between AOD and PM is not explicit and there are unknowns that cause uncertainties in this relationship.The relationship between MODIS AOD and ground-based PM10 has been studied on the basis of a large data set where daily averaged PM10 data from the 12 air quality stations across Croatia over the 5 year period are correlated with AODs retrieved from MODIS Terra and Aqua. A database was developed to associate coincident MODIS AOD (independent) and PM10 data (dependent variable). Additional tested independent variables (predictors, estimators) included season, cloud fraction, and meteorological parameters — including temperature, air pressure, relative humidity, wind speed, wind direction, as well as planetary boundary layer height — using meteorological data from WRF (Weather Research and Forecast) model.It has been found that 1) a univariate linear regression model fails at explaining the data variability well which suggests nonlinearity of the AOD-PM10 relationship, and 2) explanation of data variability can be improved with multivariate linear modeling and a neural network approach, using additional independent variables.

scholarly journals Aerosol optical depth thresholds as a tool to assess diffuse radiation fertilization of the land carbon uptake in China

2017 ◽  
Vol 17 (2) ◽  
pp. 1329-1342 ◽  
Author(s):  
Xu Yue ◽  
Nadine Unger
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
North China Plain ◽  
North China ◽  
Carbon Uptake ◽  
The North ◽  
The North China Plain ◽  
Haze Pollution ◽  
Aerosol Pollution ◽  
Sky Conditions

Abstract. China suffers from frequent haze pollution episodes that alter the surface solar radiation and influence regional carbon uptake by the land biosphere. Here, we apply combined vegetation and radiation modeling and multiple observational datasets to assess the radiative effects of aerosol pollution in China on the regional land carbon uptake for the 2009–2011 period. First, we assess the inherent sensitivity of China's land biosphere to aerosol pollution by defining and calculating two thresholds of aerosol optical depth (AOD) at 550 nm, (i) AODt1, resulting in the maximum net primary productivity (NPP), and (ii) AODt2, such that if local AOD < AODt2, the aerosol diffuse fertilization effect (DFE) always promotes local NPP compared with aerosol-free conditions. Then, we apply the thresholds, satellite data, and interactive vegetation modeling to estimate current impacts of aerosol pollution on land ecosystems. In the northeast, observed AOD is 55 % lower than AODt1, indicating a strong aerosol DFE on local NPP. In the southeastern coastal regions, observed AOD is close to AODt1, suggesting that regional NPP is promoted by the current level of aerosol loading, but that further increases in AOD in this region will weaken the fertilization effects. The North China Plain experiences limited enhancement of NPP by aerosols because observed AOD is 77 % higher than AODt1 but 14 % lower than AODt2. Aerosols always inhibit regional NPP in the southwest because of the persistent high cloud coverage that already substantially reduces the total light availability there. Under clear-sky conditions, simulated NPP shows widespread increases of 20–60 % (35.0 ± 0.9 % on average) by aerosols. Under all-sky conditions, aerosol pollution has spatially contrasting opposite sign effects on NPP from −3 % to +6 % (1.6 ± 0.5 % on average), depending on the local AOD relative to the regional thresholds. Stringent aerosol pollution reductions motivated by public health concerns, especially in the North China Plain and the southwest, will help protect land ecosystem functioning in China and mitigate long-term global warming.

scholarly journals Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory – Pyramid (5079 m a.s.l.)

2010 ◽  
Vol 10 (1) ◽  
pp. 1193-1220 ◽  
Author(s):  
G. P. Gobbi ◽  
F. Angelini ◽  
P. Bonasoni ◽  
G. P. Verza ◽  
A. Marinoni ◽  
...  
Keyword(s):  
High Altitude ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Monsoon Season ◽  
Good Reason ◽  
Single Scattering ◽  
Radiative Properties ◽  
Mountain Range ◽  
Monsoon Period

Abstract. In spite of being located at the heart of the highest mountain range in the world, the Himalayan Nepal Climate Observatory (5079 m a.s.l.) at the Ev-K2-CNR Pyramid is shown to be affected by the advection of pollution aerosols from the populated regions of southern Nepal and the Indo-Gangetic plains. Such an impact is observed along most of the period April 2006–March 2007 addressed here, with a minimum in the monsoon season. Backtrajectory-analysis indicates long-range transport episodes occurring in this period to originate mainly in the West Asian deserts. At this high altitude site, the measured aerosol optical depth is observed to be: 1) about one order of magnitude lower than the one measured at Gandhi College (60 m a.s.l.), in the Indo-Gangetic basin, and 2) maximum during the monsoon period, due to the presence of elevated (cirrus-like) particle layers. Assessment of the aerosol radiative forcing results to be hampered by the persistent presence of these high altitude particle layers, which impede a continuous measurement of both the aerosol optical depth and its radiative properties from sky radiance inversions. Even though the retrieved absorption coefficients of pollution aerosols was rather large (single scattering albedo of the order of 0.6–0.9 were observed in the month of April 2006), the corresponding low optical depths (~0.03 at 500 nm) are expected to limit the relevant radiative forcings. Still, the high specific forcing of this aerosol and its capability of altering snow surface albedo provide good reason for continuous monitoring.

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