A33C-01
Radiative Effects of African Dust and Smoke Observed from CERES and CALIOP Data
Cloud and aerosol effects have a significant impact on the atmospheric radiation budget in the Tropical Atlantic because of the spatial and temporal extent of desert dust and smoke from biomass burning in the atmosphere. The influences of African dust and smoke aerosols on cloud radiative properties over the Tropical Atlantic Ocean were analyzed for the month of July for three years (2006-2008) using collocated data collected by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the CALIPSO and Aqua satellites. On average, clouds below 5 km had a daytime instantaneous shortwave (SW) radiative flux of about 270 W/m2 and thin cirrus clouds had a SW radiative flux of about 208 W/m2. When dust and smoke aerosols interacted with clouds below 5 km, as determined from CALIPSO, the SW radiative flux decreased to as low as roughly 205 W/m2. These decreases in SW radiative flux were likely attributed to the aerosol layer height and changes in cloud microphysics (semi- direct effect). CALIOP lidar observations, which more accurately identify aerosol layer height than passive instruments, appear essential for better understanding of cloud-aerosol interactions, a major uncertainty in predicting the climate system.
A33C-02
A 10-yr Climatology of Arctic Cloud Fraction and Surface Radiation Budget at Barrow, Alaska
A 10-yr record of Arctic cloud fraction and surface radiation budget has been generated using data collected from June 1998 to May 2008 at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) site and the nearby NOAA Barrow Observatory (BRW). The record includes the seasonal variations of cloud fraction (CF), cloud liquid water path (LWP), precipitable water vapor (PWV), surface albedo, shortwave (SW) and longwave (LW) fluxes and cloud radative forcings (CRFs), as well as their decadal variations. Values of CF derived from different instruments and methods agree well, having an annual average of ~0.74. Cloudiness increases from March to May, remains high (~0.8-0.9) from May to October, and then decreases over winter. More clouds and higher LWP and PWV occurred during the warm season (May-October) than the cold season (November-April). These results are strongly associated with southerly flow which transports warm, moist air masses to Barrow from the North Pacific and over area of Alaska already free of snow during the warm season and with a dipole pattern of pressure in which a high is centered over the Beaufort Sea and low over the Aleutians during the cold season. The monthly means of estimated clear-sky and measured all-sky SW-down and LW-down fluxes at the two facilities are almost identical with the annual mean differences less than 1.6 W m-2. The downwelling and upwelling LW fluxes remain almost constant from January to March, then increase from March and peak during July-August. SW-down fluxes are primarily determined by seasonal changes in the intensity and duration of insolation over Northern Alaska, and are also strongly dependent on cloud fraction and optical depth, and surface albedo. The monthly variations of NET CRF generally follow the cycle of SW CRF, modulated by LW effects. On annual average, the negative SW CRF and positive LW CRF tend to cancel, resulting in annual average NET CRF of 2-4.5 Wm-2. Arctic clouds have a net warming effect on the surface throughout the year, with exception of the snow-free period from middle June to middle September when there tends to be a cooling effect. The daily average surface albedos agree well at the two sites remaining high (>0.8) until late May, dropping below 0.2 after the snow melts around June and increasing during autumn once snow begins to accumulate. On the basis of long-term regression analyses CF has decreased by about 0.048 while temperature has risen by ~ 1.1 K over the 10-yr period, which can be characterized by tendencies of warming mainly during December and April. With regard to the 2007 record minimum Arctic ice extent, this study provides additional empirical evidence that decreased cloud cover and increased SW-down flux during summer contributed to anomalous ice melt in the region north of Barrow. At Barrow, average June- August CF decreased by 0.062 in 2007 from the 10-yr mean, while SW-down and NET fluxes increased by 28.4 Wm-2 and 11.3 Wm-2, respectively. The increase in the NET radiative flux during summer 2007 most likely contributed to an increase in surface air temperature of 1.6 K.
A33C-03
Water Vapor Observations at ALOMAR Over a Solar Cycle and Calculations by Means of the Real Date Model LIMA
Microwave water vapor measurements between 40 and 80 km altitude over a solar cycle (1996-2006) were carried out in high latitudes at ALOMAR (69.29 N, 16.03 E), Norway. Some smaller gapes and three interruptions of monitoring in the winters 1996/1997 and 2005/2006 and from spring 2001 to spring 2002 occurred during this period. The observations are marked by a distinct year-to-year variability not directly related to the solar activity. In the upper domain in winter the water vapor mixing ratios are anti-correlated to the solar activity whereas in summer minima occurred in the years after the solar maximum in 2000/2001. In winter sudden stratospheric warmings (SSWs) modulate the water vapor mixing ratios. Within the stratopause region a middle atmospheric water vapor maximum was observed. It results from the methane oxidation and is a regular feature there. The maximum altitude increases from winter toward summer by approximately 5 km. During the summer season a secondary water vapor maximum in altitude occurred above 65 km most pronounced in late summer. The solar Lyman-alpha radiation impacts the water vapor mixing ratio particularly above 65 km in winter. In summer the correlation is rather positive below the upper mesosphere. A strong day- to-day variability connected with planetary wave activity was found over the whole year. Although model calculations by means of the real date model LIMA (Leibniz-Institute Middle Atmosphere model) reflect essential patterns of the water vapor variation the results also show differences to the observations. We show results of measurements and compare these with calculations and discuss the chemical and dynamical background of the variation of water vapor in the high latitude mesosphere.
A33C-04
Based on LSRMAM ICA-Batch Processing for Spectral Unmixing in Remote Sensing
The individual pixels in remote sensing multispectral images are generally compounded as the sum of the radiances of all materials within the instantaneous filed of view of the sensor. Those pixels are called mixed pixels. The decomposition of mixed pixels is constantly an on-going research topic in remote sensing. The current decomposition models have the following characteristics: linear, probability-statistical, random geometric, geometric optical and fuzzy etc. Linear spectral random mixture analysis model (LSMAM) is the most commonly used model for sub-pixel detection and mixed pixel classification at the current time. It is built on the assumption that the same materials within pixels possess the same spectral characteristics as linear additive model. Its structure is simple along with clear theoretical and physical interpretation. There is a better way that assumes the composition of each of the mixed pixels to be a random variable, i.e. a random signal source, and the spectral response curves of ground types are independent to each other. In this way, each of the spectral response curves constitutes a source signal so that the multispectral image can be considered as a mixture of these source signals. Thus the classification of this mixture turns into a blind source separation task, which is no other than the mathematical model of ICA (independent component analysis). Batch processing is one type of linear ICA approaches that are based on high-order statistics. Its core is to use the high order cumulants matrix to optimize the goal function through the Givens transformation. JADE, SHIBBS and JCC algorithms are commonly used at the current time. As the great virtue, the ICA-Batch processing does not require estimating the probability density function of the mixed signal, and is able to process the mixed signal that contains super-Gaussian and sub-Gaussian signals as well. Furthermore, the sum-to-one constraint can be applied to the ICA-Batch processing so that the weighting matrix f and composition matrix A can be resulted through a group of pixels simultaneously. This helps to solve the problem with the ambiguous magnitudes towards a half quantitative analysis of the decomposition of the mixed pixels. This paper studies the constrained ICA-Batch processing approach and compares its solutions with the ones obtained from conventional methods using simulated and real data, respectively. Satisfied solutions have been achieved. At the same time, different batch processing algorithms are compared to each other. In case that the data contains two or more Gaussian signals, JCC method is capable of decomposing the signals, but the JADE method does not show good performance. Accordingly, the batch processing provides low computational efficiency with huge volume of data.
A33C-05
Spatial Correlations of Aerosol Optical Depth Over Land
The accurate atmospheric correction of historical satellite long-term data is required to make them suitable for climate change application. This is essential to properly identify the impacts caused by changing surface properties, such as vegetation, soil and snow cover, rather than atmospheric effects, cloud contamination and artefacts. The correction of satellite data over land for aerosol effect constitutes the most challenging part of the processing. While a good progress in aerosol retrievals has been achieved in recent years using the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging Spectroradiometer (MISR), the aerosol properties and their associated impact on atmospheric correction for historical data over land from the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA satellites for pre-MODIS period is still not adequately addressed. It seems promising to develop the AVHRR atmospheric correction algorithm based on the synthesis of aerosol retrievals over dark targets and optimum interpolation technique based on aerosol spatio-temporal statistics. The implementation of this approach requires the knowledge of aerosol spatial correlation function. The estimates of aerosol optical depth (AOD) spatial correlation function were obtained in this study using different data sources: MODIS level 2 and level 3 aerosol products, daily averages of ground sun photometer aerosol retrievals from Aerosol Robotic Network (AERONET) and the global chemistry and aerosol atmospheric transport model results from NASA's GOCART. The AOD correlation properties obtained from different types of MODIS aerosol products were found in reasonably good agreement with each other. The AOD correlation radius for different types of MODIS data varied from 418 km to 900 km. The AOD correlation radius obtained from AERONET data was found to be close to 500km. Substantial differences were detected between AOD spatial correlation function derived from MODIS satellite product and atmospheric transport model results. We will discuss the details of intercomparison and possible explanations for observed results.
A33C-06
Nocturnal Boundary Layer Measurements during the Amazonian Aerosol Characterization Experiment (AMAZE)
To characterize the Nocturnal Boundary Layer (NBL) hourly profiles of wind, pressure, temperature, humidity and 5 sizes particles concentration, were made by using tethered balloon at INPA tropical Amazon rainforest Reserve (Cuieiras) 100 km northwest from Manaus city. The measurements were made during the wet season March/2008. The NBL height was 100 to 150m, with a very well mixed layer close to surface associate with temperature inversion. The wind profiles shows a very clear low level in two nights, about 500 to 900 m, and, in general, all nights show an stable and cooler air layer close the surface uncoupled with outer residual boundary layer above. At the site a very clear drainage flow from north quadrant down slope eastward quadrant during very the stable cases. This findings is correlates with particles profiles where was commonly trapped by stable layer presenting high concentrations, for all 5 sizes measured, close to the surface at vegetation level and just above it. All nights presents high humidity with fog formation in three cases, associates with temperature below the 23ºC. The wind speed were very low about 0.5 to calm, in generally associate with drainage flow down hill. The NBL dynamics is a discussion issue associate to the aerosol nocturnal mixing in complex terrain with tall vegetation, the currently AMAZE site case.
A33C-07
Surface Reflectivity From OMI Using Aqua MODIS to Eliminate Clouds: Effects of Snow on OMI NO2 Retrievals
Satellite retrievals of tropospheric trace gases such as NO2 require accurate information about surface reflectivity. We use cloud-free data from the Ozone Monitoring Instrument (OMI) onboard the Aura satellite to determine global surface reflectivity under both snow covered and snow free conditions. Cloud-free scenes are determined using the cloud mask from the Moderate Resolution Imaging Spectroradiometer (MODIS). MODIS is located onboard the Aqua satellite which flies approximately 15 minutes ahead of Aura in the NASA A-Train. The result is a database of surface reflectivity from OMI that does not rely on statistical methods to eliminate cloud cover. The MODIS cloud discrimination also enables verification that a scene is cloud-free even in the presence of non-climatological snow cover. Surface reflectivity over snow covered lands is observed to depend strongly on the type of vegetation covering the surface. We find that applying our snow surface reflectivity database to the OMI NO2 retrieval would significantly change the retrieved NO2 columns.
A33C-08
Analysis of MODIS and DC-8 in-situ dust properties during NAMMA
The NASA African Monsoon Multidisciplinary Analyses (NAMMA) 2006 field campaign provided a unique opportunity for examining dust properties during the summer frequent dust outbreaks. This study analyzes the MODIS-derived aerosol properties and DC-8 in-situ measurements with special focuses on the dust aerosol optical depth and effective radius. In addition, dust layer height will also be studied. MODIS-derived dust layer height using water vapor absorption deficiency in the presence of dust layer will be compared with observed dust extinction profiles. The associated spatial and vertical variabilities of the dust properties will be evaluated for future model analysis. Time series of MODIS aerosol optical depth and effective radius will be analyzed retrospectively in the NAMMA domain since the launch of EOS Terra satellite in 2000. The differences between Terra and Aqua MODIS will also be examined.
A33C-09
Multi-event analysis of Lidar and Sunphotometer observations acquired at a site in Southern Canada
Knowledge of the long-range transport and evolution of aerosols originating from natural and anthropogenic sources plays a vital role in understanding their impact on the composition of the atmosphere and on the climate system. Wealth of information from ground-based instrument networks, field experiments helped to establish aerosol transport pathways over the globe in addition to passive remote sensing satellite instruments. Frequent ground-based measurements were carried out over a multi-year period using lidar and Sun photometry/Sky radiometry) over the Environment Canada (CARE) site at Egbert (44.220 N, 79.750 W), Ontario, Canada. The goals of these measurements was to better understand the optical coherency between active and passive remote sensing techniques in a variety of aerosol conditions and eventually to achieve a preliminary climatology of intensive aerosol optical parameters.
A33C-10
MAESTRO Measurements of Atmospheric Aerosol Extinction
ABSTRACT: Aerosols in the atmosphere both scatter and absorb light. Uncertainty in the magnitude of these effects on atmospheric radiation is one of the biggest uncertainties in estimates of the radiative forcing of climate. The Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) experiment on the Atmospheric Chemistry (ACE) satellite is making measurements of optical depth in the atmosphere which are analyzed to produce aerosol extinction profiles. The satellite was launched in 2003 and is still functioning nominally. The MAESTRO instrument and the retrieval technique will be described and some extinction profiles will be discussed.
A33C-11
Comparison of Two Cloud Condensation Nuclei Counters: An Analysis of Ground and Airborne Measurements
The University of Wyoming (UWyo) cloud condensation nuclei (CCN) counter has been used for over 10 years in many field projects. The Droplet Measurement Technologies (DMT) CCN counter has been available since 2004 and has started to be increasingly used in field projects. This scientific study focuses on comparing these two different types of CCN counters. The objective of the comparison is to allow airborne field measures made with the two different counters to be judged on a similar base. Laboratory measurements were conducted using the UWyo CCN counter, the DMT CCN counter, a Condensation Particle Counter (CPC) and an Optical Particle Counter (OPC) to measure poly-dispersed Ammonium Sulfate particles. The CPC and OPC were used to independently monitor the concentration and spectrum of the generated particles. The DMT CCN counter was found to count 10-50 % higher than the UWyo CCN counter for superstations in the range of 0.6 to 1.0 %. At 0.2 %, the DMT CCN counter measure is almost 3 times the Uwyo CCN counter. The ratio of the DMT to Uwyo CCN concentration was independent of the DMT CCN counter chamber pressure.
A33C-12
Optical Properties of Aerosols over an Urban Coastal Site in France and its Effect on Direct Radiative Forcing
Continuous measurements of aerosol physical and optical properties were carried over Toulon, an urban coastal location in south France, for one complete seasonal cycle during 2005-2006. Columnar aerosol optical depth (AOD), black carbon (BC), absorption and scattering coefficients, number-size distributions of fine and coarse particles were measured, along with the surface meteorological parameters. Monthly-mean aerosol optical depth at 440 nm ranged between 0.1 and 0.34, with high Angstrom coefficient (á >1.2). The single scattering albedo (SSA) estimated at the surface at 525 nm ranged between 0.7 and 0.8, indicating significant absorption. The presence of aerosols over the Mediterranean zone during summer decreases the shortwave radiation reaching the surface by as much as 26 ± 3.9 W/m2, and increases the top of the atmosphere reflected radiation by as much as 5.2 ± 1.0 W/m2. The shortwave atmospheric absorption translates to an atmospheric heating of 2.5 to 4.6 K/day.