scholarly journals Study of successive contrasting monsoons (2001–2002) in terms of aerosol variability over a tropical station Pune, India

2010 ◽  
Vol 10 (1) ◽  
pp. 29-37 ◽  
Author(s):  
R. L. Bhawar ◽  
P. C. S. Devara
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Regional Scale ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Cloud Formation ◽  
Activation Process ◽  
Absorbing Aerosols ◽  
Meteorological Features ◽  
Tropical Station

Abstract. The present study suggests that aerosols play a major role in cloud formation and affect significantly the precipitation over a regional scale. The study reveals that there is a high variability of aerosol index during a bad monsoon year 2002, indicating an extension of cycle to more than 100 days from a normal 50 day cycle of absorbing and non-absorbing aerosols over a tropical urban station Pune. Pre-monsoon of 2002 shows a high loading of coarse-mode aerosols (absorbing dust aerosols) which indicate vertical and horizontal temperature variations in turn affecting the seasonal rainfall at a regional scale. Cloud formation highly depends on aerosol concentration, but the activation process is not monotonic. The surface meteorological features help to initiate the cloud process. The surface temperatures were high during the pre-monsoon of 2002 leading to increase of aerosol optical depth as compared to 2001. The effect of surface wind speed, though, complicated to understand, results in low values in 2002 with high aerosol optical depth and vice-versa in 2001.

scholarly journals Study of successive contrasting monsoons (2001–2002) in terms of aerosol variability over a tropical station Pune, India

2009 ◽  
Vol 9 (2) ◽  
pp. 6957-6977 ◽  
Author(s):  
R. L. Bhawar ◽  
P. C. S. Devara
Keyword(s):  
Wind Speed ◽  
Regional Scale ◽  
High Variability ◽  
Cloud Formation ◽  
Urban Station ◽  
Temperature Variations ◽  
Absorbing Aerosols ◽  
Meteorological Features ◽  
Tropical Station ◽  
Aerosol Index

Abstract. The present study confirms that aerosols play a major role in cloud formation and affect significantly the precipitation over a regional scale. The study here shows that there is a high variability of aerosol index during a bad monsoon year 2002 indicating an extension of cycle to more than 100 days from a normal 50 day cycle of absorbing and non- absorbing aerosols over a tropical urban station Pune. Pre-monsoon 2002 shows a high loading of coarse mode aerosols (absorbing aerosols) which indicates vertical and horizontal temperature variations in turn affecting the seasonal rainfall at a regional scale. Cloud formation highly depends on aerosol concentration, where surface meteorological features are essential to initiate the process. The surface temperatures were high during the pre-monsoon of 2002 as compared to 2001. The effect of wind speed though, complicated to understand, reveal low values in 2002 with high aerosol optical depth and vice versa in 2001.

scholarly journals Estimating the maritime component of aerosol optical depth and its dependency on surface wind speed using satellite data

2010 ◽  
Vol 10 (14) ◽  
pp. 6711-6720 ◽  
Author(s):  
Y. Lehahn ◽  
I. Koren ◽  
E. Boss ◽  
Y. Ben-Ami ◽  
O. Altaratz
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Time Scale ◽  
Time Lag ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Time Frame ◽  
Marine Aerosol ◽  
Wind Intensity

Abstract. Six years (2003–2008) of satellite measurements of aerosol parameters from the Moderate Resolution Imaging Spectroradiometer (MODIS) and surface wind speeds from Quick Scatterometer (QuikSCAT), the Advanced Microwave Scanning Radiometer (AMSR-E), and the Special Sensor Microwave Imager (SSM/I), are used to provide a comprehensive perspective on the link between surface wind speed and marine aerosol optical depth over tropical and subtropical oceanic regions. A systematic comparison between the satellite derived fields in these regions allows to: (i) separate the relative contribution of wind-induced marine aerosol to the aerosol optical depth; (ii) extract an empirical linear equation linking coarse marine aerosol optical depth and wind intensity; and (iii) identify a time scale for correlating marine aerosol optical depth and surface wind speed. The contribution of wind induced marine aerosol to aerosol optical depth is found to be dominated by the coarse mode elements. When wind intensity exceeds 4 m/s, coarse marine aerosol optical depth is linearly correlated with the surface wind speed, with a remarkably consistent slope of 0.009±0.002 s/m. A detailed time scale analysis shows that the linear correlation between the fields is well kept within a 12 h time frame, while sharply decreasing when the time lag between measurements is longer. The background aerosol optical depth, associated with aerosols that are not produced in-situ through wind driven processes, can be used for estimating the contributions of terrestrial and biogenic marine aerosol to over-ocean satellite retrievals of aerosol optical depth.

scholarly journals Aerosol optical depth trend over the Middle East

2016 ◽  
Author(s):  
K. Klingmüller ◽  
A. Pozzer ◽  
S. Metzger ◽  
G. Stenchikov ◽  
J. Lelieveld
Keyword(s):  
Saudi Arabia ◽  
Soil Moisture ◽  
Middle East ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Surface Winds ◽  
Anthropogenic Aerosol ◽  
Dust Emissions

Abstract. We use the combined Dark Target/Deep Blue aerosol optical depth (AOD) satellite product of the Moderate-resolution Imaging Spectroradiometer (MODIS) collection 6 to study trends over the Middle East between 2000 and 2015. Our analysis corroborates a previously identified positive AOD trend over large parts of the Middle East during the period 2001 to 2012. We relate the annual AOD to precipitation, soil moisture and surface winds to identify regions where these attributes are directly related to the AOD over Saudi Arabia, Iraq and Iran. Regarding precipitation and soil moisture, a relatively small area in and surrounding Iraq turns out to be of prime importance for the AOD over these countries. Regarding surface wind speed, the African Red Sea coastal area is relevant for the Saudi Arabian AOD. Using multiple linear regression we show that AOD trends and interannual variability can be attributed to soil moisture, precipitation and surface winds, being the main factors controlling the dust cycle. Our results confirm the dust driven AOD trends and variability, supported by a decreasing MODIS-derived Ångström exponent and a decreasing AERONET-derived fine mode fraction that accompany the AOD increase over Saudi Arabia. The positive AOD trend relates to a negative soil moisture trend. As a lower soil moisture translates into enhanced dust emissions, it is not needed to assume growing anthropogenic aerosol and aerosol precursor emissions to explain the observations. Instead, our results suggest that increasing temperature and decreasing relative humidity in the last decade have promoted soil drying, leading to increased dust emissions and AOD; consequently an AOD increase is expected due to climate change.

scholarly journals Effect of wind speed on aerosol optical depth over remote oceans, based on data from the Maritime Aerosol Network

2012 ◽  
Vol 5 (2) ◽  
pp. 377-388 ◽  
Author(s):  
A. Smirnov ◽  
A. M. Sayer ◽  
B. N. Holben ◽  
N. C. Hsu ◽  
S. M. Sakerin ◽  
...  
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Correlation Coefficients ◽  
Surface Wind Speed ◽  
Near Surface ◽  
Strong Winds ◽  
The Relationship ◽  
Good Agreement

Abstract. The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. The MAN archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we investigate correlations between ship-borne aerosol optical depth (AOD) and near-surface wind speed, either measured (onboard or from satellite) or modeled (NCEP). According to our analysis, wind speed influences columnar aerosol optical depth, although the slope of the linear regression between AOD and wind speed is not steep (~0.004–0.005), even for strong winds over 10 m s−1. The relationships show significant scatter (correlation coefficients typically in the range 0.3–0.5); the majority of this scatter can be explained by the uncertainty on the input data. The various wind speed sources considered yield similar patterns. Results are in good agreement with the majority of previously published relationships between surface wind speed and ship-based or satellite-based AOD measurements. The basic relationships are similar for all the wind speed sources considered; however, the gradient of the relationship varies by around a factor of two depending on the wind data used.

scholarly journals Aerosol optical depth trend over the Middle East

2016 ◽  
Vol 16 (8) ◽  
pp. 5063-5073 ◽  
Author(s):  
Klaus Klingmüller ◽  
Andrea Pozzer ◽  
Swen Metzger ◽  
Georgiy L. Stenchikov ◽  
Jos Lelieveld
Keyword(s):  
Saudi Arabia ◽  
Soil Moisture ◽  
Middle East ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Surface Winds ◽  
Anthropogenic Aerosol ◽  
Dust Emissions

Abstract. We use the combined Dark Target/Deep Blue aerosol optical depth (AOD) satellite product of the moderate-resolution imaging spectroradiometer (MODIS) collection 6 to study trends over the Middle East between 2000 and 2015. Our analysis corroborates a previously identified positive AOD trend over large parts of the Middle East during the period 2001 to 2012. We relate the annual AOD to precipitation, soil moisture and surface winds to identify regions where these attributes are directly related to the AOD over Saudi Arabia, Iraq and Iran. Regarding precipitation and soil moisture, a relatively small area in and surrounding Iraq turns out to be of prime importance for the AOD over these countries. Regarding surface wind speed, the African Red Sea coastal area is relevant for the Saudi Arabian AOD. Using multiple linear regression we show that AOD trends and interannual variability can be attributed to soil moisture, precipitation and surface winds, being the main factors controlling the dust cycle. Our results confirm the dust driven AOD trends and variability, supported by a decreasing MODIS-derived Ångström exponent and a decreasing AERONET-derived fine mode fraction that accompany the AOD increase over Saudi Arabia. The positive AOD trend relates to a negative soil moisture trend. As a lower soil moisture translates into enhanced dust emissions, it is not needed to assume growing anthropogenic aerosol and aerosol precursor emissions to explain the observations. Instead, our results suggest that increasing temperature and decreasing relative humidity in the last decade have promoted soil drying, leading to increased dust emissions and AOD; consequently an AOD increase is expected due to climate change.

scholarly journals Accuracy assessment of Aqua-MODIS aerosol optical depth over coastal regions: importance of quality flag and sea surface wind speed

2012 ◽  
Vol 5 (4) ◽  
pp. 5205-5243 ◽  
Author(s):  
J. C. Anderson ◽  
J. Wang ◽  
J. Zeng ◽  
M. Petrenko ◽  
G. G. Leptoukh ◽  
...  
Keyword(s):  
Wind Speed ◽  
Density Function ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Open Ocean ◽  
Sea Surface ◽  
Coastal Regions ◽  
Modis Aod

Abstract. Coastal regions around the globe are a major source for anthropogenic aerosols in the atmosphere, but the underlying surface characteristics are not favorable for the Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms designed for retrieval of aerosols over dark land or open-ocean surfaces. Using data collected from 62 coastal stations worldwide from the Aerosol Robotic Network (AERONET) from ~ 2002–2010, accuracy assessments are made for coastal aerosol optical depth (AOD) retrieved from MODIS aboard Aqua satellite. It is found that coastal AODs (at 550 nm) characterized respectively by the MODIS Dark Land (hereafter Land) surface algorithm, the Open-Ocean (hereafter Ocean) algorithm, and AERONET all exhibit a log-normal distribution. After filtering by quality flags, the MODIS AODs respectively retrieved from the Land and Ocean algorithms are highly correlated with AERONET (with R2 &amp;approx; 0.8), but only the Land algorithm AODs fall within the expected error envelope greater than 66% of the time. Furthermore, the MODIS AODs from the Land algorithm, Ocean algorithm, and combined Land_and_Ocean product show statistically significant discrepancies from their respective counterparts from AERONET in terms of mean, probability density function, and cumulative density function, which suggest a need for future improvement in retrieval algorithms. Without filtering with quality flag, the MODIS Land_and_Ocean AOD dataset can be degraded by 30–50% in terms of mean bias. Overall, the MODIS Ocean algorithm overestimates the AERONET coastal AOD by 0.021 for AOD < 0.25 and underestimates it by 0.029 for AOD > 0.25. This dichotomy is shown to be related to the ocean surface wind speed and cloud contamination effects on the satellite aerosol retrieval. The Modern Era Retrospective-Analysis for Research and Applications (MERRA) reveals that wind speeds over the global coastal region (with a mean and median value of 2.94 m s−1 and 2.66 m s−1, respectively) are often slower than 6 m s−1 assumed in the MODIS Ocean algorithm. As a result of high correlation (R2 > 0.98) between the bias in binned MODIS AOD and the corresponding binned wind speed over the coastal sea surface, an empirical scheme for correcting the bias of AOD retrieved from the MODIS Ocean algorithm is formulated and is shown to be effective over the majority of the coastal AERONET stations, and hence can be used in future analysis of AOD trend and MODIS AOD data assimilation.

scholarly journals Effect of wind speed on aerosol optical depth over remote oceans, based on data from the Maritime Aerosol Network

2011 ◽  
Vol 4 (6) ◽  
pp. 7185-7209
Author(s):  
A. Smirnov ◽  
A. M. Sayer ◽  
B. N. Holben ◽  
N. C. Hsu ◽  
S. M. Sakerin ◽  
...  
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Correlation Coefficients ◽  
Surface Wind Speed ◽  
Near Surface ◽  
Strong Winds ◽  
The Relationship ◽  
Good Agreement

Abstract. The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. The MAN archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we investigate correlations between ship-borne aerosol optical depth (AOD) and near-surface wind speed, either measured (onboard or from satellite) or modeled (NCEP). According to our analysis, wind speed influences columnar aerosol optical depth, although the slope of the linear regression between AOD and wind speed is not steep (∼0.004–0.005), even for strong winds over 10 m s−1. The relationships show significant scatter (correlation coefficients typically in the range 0.3–0.5); the majority of this scatter can be explained by the uncertainty on the input data. The various wind speed sources considered yield similar patterns. Results are in good agreement with the majority of previously published relationships between surface wind speed and ship-based or satellite-based AOD measurements. The basic relationships are similar for all the wind speed sources considered; however, the gradient of the relationship varies by around a factor of two depending on the wind data used.

scholarly journals Estimating the maritime component of aerosol optical depth and its dependency on surface wind speed using MODIS and QuikSCAT data

2010 ◽  
Vol 10 (1) ◽  
pp. 1983-2003 ◽  
Author(s):  
Y. Lehahn ◽  
I. Koren ◽  
E. Boss ◽  
Y. Ben-Ami ◽  
O. Altaratz
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
World Ocean ◽  
Surface Wind Speed ◽  
Marine Aerosol ◽  
Coarse Mode ◽  
Wind Intensity ◽  
Threshold Wind Speed

Abstract. Seven years (2002–2008) of satellite measurements from SeaWinds aboard Quick Scatterometer (QuikSCAT) and Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra are used for providing a global view on the link between surface wind speed and marine aerosol optical depth. This study shows that away form the continents the correlation time between the surface winds and the marine aerosol exceeds 4 h and therefore the two measurements can be linked. A systematic comparison between the satellite derived fields at different locations over the World Ocean allows to: (i) separate the relative contribution of wind-induced marine aerosol to the aerosol optical depth (ii) identify a threshold wind speed for triggering maritime contribution to aerosol optical depth; and (iii) extract an empirical linear equation linking marine aerosol optical depth and wind intensity. Wind induced marine aerosol contribution to aerosol optical depth is found to be dominated by the coarse mode elements. The threshold wind speed for triggering emission of coarse maritime aerosol is remarkably consistent with an average value of 4.1±0.1 m/s. When wind intensity exceeds the threshold value, coarse mode marine aerosol optical depth is linearly correlated to the surface wind speed, with a consistent slope of 0.0082±0.0004 s/m. The background aerosol optical depth, associated with aerosols that are not produced in-situ through wind driven processes, shows relatively large seasonal and geographical variability, and can be used for estimating the contribution of terrestrial aerosols to the aerosol optical depth over the ocean.

scholarly journals Observations of rapid aerosol optical depth enhancements in the vicinity of polluted cumulus clouds

2014 ◽  
Vol 14 (21) ◽  
pp. 11633-11656 ◽  
Author(s):  
T. F. Eck ◽  
B. N. Holben ◽  
J. S. Reid ◽  
A. Arola ◽  
R. A. Ferrare ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Diurnal Cycle ◽  
Airborne Lidar ◽  
Cloud Formation ◽  
Aerosol Size Distribution ◽  
Cumulus Clouds ◽  
Cloud Processing ◽  
Aerosol Scattering ◽  
Fine Mode

Abstract. During the July 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field experiment in Maryland, significant enhancements in Aerosol Robotic Network (AERONET) sun–sky radiometer measured aerosol optical depth (AOD) were observed in the immediate vicinity of non-precipitating cumulus clouds on some days. Both measured Ångström exponents and aerosol size distribution retrievals made before, during and after cumulus development often suggest little change in fine mode particle size; therefore, implying possible new particle formation in addition to cloud processing and humidification of existing particles. In addition to sun–sky radiometer measurements of large enhancements of fine mode AOD, lidar measurements made from both ground-based and aircraft-based instruments during the experiment also measured large increases in aerosol signal at altitudes associated with the presence of fair weather cumulus clouds. These data show modifications of the aerosol vertical profile as a result of the aerosol enhancements at and below cloud altitudes. The airborne lidar data were utilized to estimate the spatial extent of these aerosol enhancements, finding increased AOD, backscatter and extinction out to 2.5 km distance from the cloud edge. Furthermore, in situ measurements made from aircraft vertical profiles over an AERONET site during the experiment also showed large increases in aerosol scattering and aerosol volume after cloud formation as compared to before. The 15-year AERONET database of AOD measurements at the Goddard Space Flight Center (GSFC), Maryland site, was investigated in order to obtain a climatological perspective of this phenomenon of AOD enhancement. Analysis of the diurnal cycle of AOD in summer showed significant increases in AOD from morning to late afternoon, corresponding to the diurnal cycle of cumulus development.

Sign in / Sign up

Export Citation Format

Share Document