Total Ozone Mapping Spectrometer Aerosol Index Research Articles

Dust as a Potential Tracer for the Flow over Topography

The distribution of mineral dust around topographical obstacles is examined, employing the dimensionless Froude number that describes different flow regimes in a fluid. Flow around a peak with a near-circular shape in a dusty environment like the Sahara and the Sahel was examined in order to investigate the distribution of the dust around the obstacle. The Total Ozone Mapping Spectrometer Aerosol Index (TOMS-AI) daily Aerosol Index, the u and v wind components and the temperature, were used for the period 1979-1992, i.e. 14 years. It is found by the AI data that the shape of the dust distribution around the circular peak is in good agreement with the shape of the peak itself. Additionally good correlation exists between the vertical distribution of the dust above the peak and the Froude Number in its vicinity. This method allows for the first time the investigation of the flow above and around topographical obstacles in different flow conditions in the open space employing dust as the flow tracer.

Arctic oscillation and the interannual variability of dust emissions from the Tarim Basin: a TOMS AI based study

This paper examines the teleconnection between the Arctic Oscillation Index (AO) and dust activities in the Tarim Basin [in terms of the Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) level]. In this study, High Dust Active years (H) and Low Dust Active years (L) in terms of dust loading are identified. Composites of geopotential height at both 850 and 500 hPa level show that, the geopotential height level of H years is generally lower than the average, especially over the south end of the Central Siberian Plateau. The geopotential height level of L years is generally higher than the average, especially over the same region of Siberia. By correlating the AO and TOMS AI with geopotential height at different pressure levels, a South Siberia Geopotential Height Index (SSGI) is constructed. A strong positive correlation is found between AO and SSGI. Strong negative correlations are found between TOMS AI and AO, and between TOMS AI and SSGI. Through investigating the relation among these three measures (TOMS AI, AO and SSGI), we found that in the positive phase of AO, geopotential gradient between the inside and outside of the basin is small. The northerly wind from Siberia is weak and decreases when it encounters the north barrier of the basin. As a result, dust activities in the Tarim Basin is weak and Eddy Kinetic Energy (EKE) level measured in the basin is lower. In the negative phase of AO, geopotential gradient between the inside and outside of the basin is big. The northerly wind from Siberia is strong, and passes the north barrier of the basin. When it encounters the Tibetan Plateau, a component of the wind goes into the basin. During this process, the wind accelerates given the higher pressure gradient. As a result, dust activities in the Tarim Basin are frequent and intensive, and the EKE level in the basin is higher.

Reply to comment by E. Williams on “Atmospheric controls on the annual cycle of North African dust”

[01] The aim of Engelstaedter and Washington [2007a] (hereafter EW) was to analyze the long-term mean annual cycle of dust over North Africa and to assess the role of the large-scale wind in controlling the annual cycle. Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) [Herman et al., 1997] was used as it is the only spatially complete data set of dust loadings which is long enough to compute a climatology. EW report on the location of maximum AI loadings in the course of the annual cycle and show that these are found in close spatial association with the near surface wind divergence minima and are all in the central Sahara. These maxima colocate with the Saharan summer heat low and where dry convection extends beyond 5 km in summer in one of the deepest boundary layers on the planet. [2] Williams [2008] notes that in the EW ‘‘review’’ we neglect a potent source of dust production in North Africa, namely haboobs which result from moist convection in the northern fringe of the Intertropical Convergence Zone (ITCZ) and which also produces upper level cirrus. He argues that the cirrus artificially reduces the TOMS AI values in the lower troposphere. [3] There are important points of departure between EW and Williams [2008]. First, EW is not a review paper. It is the first paper to focus on the climatology of the annual cycle of dust in North Africa using a spatially complete data set. It was not the intention of EW to partition the role of specific dynamic systems in dust production. In order to investigate the role of specific dust generating systems in North Africa, including systems such as Sharav Cyclons [Moulin et al., 1998], African easterly waves [Jones et al., 2003], density currents [Knippertz et al., 2007], and also haboobs, an entirely different sampling framework would be necessary and simple averaging would not be appropriate. Some of these dust production mechanisms may be more important than others. Our view of haboobs and gust fronts associated with moist convection is that they may be an important system of dust generation in the boreal summer over the Sahara but on the basis of currently published data and observations we cannot tell. EW do not assess their role because it was not the aim of the paper to do so. But Williams [2008] provides no evidence either, other than to refer to research undertaken at a time (summer 2006) when EW was already in press and which identifies dust generation from cold outflows based on short-term monitoring distant from the central Sahara (a long-standing problem in the way that Saharan dust has been sampled [Engelstaedter et al., 2006]). It therefore remains the case that the relative role of dust generating systems in the central Sahara is unknown. It will be an important step to unravel this problem although there are dangers of doing so from sampling in the Sahel only. This will undoubtedly bias the perspective toward the role of systems in the Sahel which Engelstaedter and Washington [2007b] have already warned to have prejudiced the long-term view of North African dust sources away from the data scarce central Sahara toward the relatively well sampled Sahel.

The spatial and temporal characteristics of TOMS AI over the Tarim Basin, China

This paper has a dual focus. One is to study the spatial characteristics of dust activities over the Tarim Basin by locating dust active hot spots. The other is to study the temporal characteristics of dust activities over the Tarim Basin by applying the Extreme Value Analysis (EVA). Hot spots (in terms of dust loading) refer to relatively small (compared to the size of the whole source area), consistently active, dust producing areas. In this paper, Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) is used to identify hot spots in the Tarim Basin. This hot spot study suggests that dust emissions are inhomogeneous in the Tarim Basin area and the formation of the two hot spots is linked to both (1) a large amount of fine sandy sediments accumulated at the hot spot areas and (2) the basin's internal dust transport pathways which are controlled by the extreme bounding topography of the basin. Extreme Value Analysis (EVA) has been widely used in a variety of areas, but has not yet been applied in dust storm research. In this paper, 13 years Tarim Basin regional daily maximum TOMS AI data time series are constructed. By examining the statistics of the time series, a new method (outlier method) is developed to identify extreme values. EVA is applied and 100-year-return values are suggested. The interpretation of the 100-year-return values is discussed by referring to historical meteorological records and also climate change projections.

Does the Madden‐Julian Oscillation influence aerosol variability?

We investigate the modulation of aerosols by the Madden‐Julian Oscillation (MJO) using multiple, global satellite aerosol products: aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus‐7, and aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on NOAA satellites. A composite MJO analysis indicates that large variations in the TOMS AI and MODIS/AVHRR AOT are found over the equatorial Indian and western Pacific Oceans where MJO convection is active, as well as the tropical Africa and Atlantic Ocean where MJO convection is weak but the background aerosol level is high. A strong inverse linear relationship between the TOMS AI and rainfall anomalies, but a weaker, less coherent positive correlation between the MODIS/AVHRR AOT and rainfall anomalies, were found. The MODIS/AVHRR pattern is consistent with ground‐based Aerosol Robotic Network data. These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol‐rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol‐rainfall relationships.

El Chichon: The genesis of volcanic sulfur dioxide monitoring from space

The 1982 eruption of El Chichon inspired a new technique for monitoring volcanic clouds. Data from the Total Ozone Mapping Spectrometer (TOMS) instrument on the Nimbus-7 satellite were used to measure sulfur dioxide in addition to ozone. For the first time precise data on the sulfur dioxide mass in even the largest explosive eruption plumes could be determined. The plumes could be tracked globally as they are carried by winds. Magmatic eruptions could be discriminated from phreatic eruptions. The data from El Chichon are reanalyzed in this paper using the latest version of the TOMS instrument calibration (V8). They show the shearing of the eruption cloud into a globe-circling band while still anchored over Mexico in three weeks. The measured sulfur dioxide mass in the initial March 28 eruption was 1.6 Tg; the April 3 eruption produced 0.3 Tg more, and the April 4 eruptions added 5.6 Tg, for a cumulative total of 7.5 Tg, in substantial agreement with estimates from prior data versions. TOMS Aerosol Index (absorbing aerosol) data show rapid fallout of dense ash east and south of the volcano in agreement with Advanced Very High Resolution Radiometer (AVHRR) ash cloud positions.

Global retrieval of columnar aerosol single scattering albedo from space‐based observations

We retrieve the global distribution of columnar single scattering albedo (ω0) by taking advantage of the high sensitivity of satellite measurements at ultraviolet channels by the Total Ozone Mapping Spectrometer (TOMS) to both aerosol optical depth and ω0 and the high sensitivity of satellite measurements at visible channels by the Moderate Resolution Imaging Spectroradiometer (MODIS) to aerosol optical depth. A radiative transfer model (LIDORT) is used to calculate the local ω0 that reproduces the TOMS aerosol index, when constrained by MODIS aerosol optical depth and by relative vertical profiles from a global chemical transport model (GEOS‐CHEM). The simulated aerosol profiles are evaluated with lidar measurements of aerosol extinction. The retrieved ω0 at 360 nm is near 1 over the remote ocean, in contrast with values of 0.75 to 0.9 over regions dominated by biomass burning and mineral dust aerosol. The retrieval uncertainty is 15%. We validate our retrieval with measurements from the Aerosol Robotic Network (AERONET); the correlation coefficient, slope, and intercept are 0.75, 0.99, and 0.02 respectively.

Aerosol optical depth and land surface reflectance from multiangle AATSR measurements: global validation and intersensor comparisons

This paper presents the results and satellite intercomparisons for the retrieval of aerosol optical depth (AOD) and land surface bidirectional reflectance using the Multiangle Advanced Along-Track Scanning Radiometer (AATSR). The algorithm developed is based on inversion of a physical model of light scattering that requires no a priori knowledge of the land surface. The model is evaluated for a number of sites around the world to test its operation over a range of aerosol types and land covers including dark and bright surfaces. Validation is performed using Aerosol Robotic Network ground-based sun-photometer measurements and by intercomparison with independent estimates of AOD derived from spaceborne instruments including Multiangle Imaging Spectroradiometer (MISR), Moderate Resolution Imaging Spectroradiometer (MODIS), and Total Ozone Mapping Spectrometer (TOMS) aerosol products. Results show good agreement (Pearson's correlation coefficient r2=0.70 for all sites combined) between the AATSR-derived estimates of AOD and the sun-photometer measurements. There is also a high correlation (r2=0.84) between the AATSR- and MISR-derived AOD estimates, but the correlations of the AATSR-derived AOD with MODIS-derived AOD and TOMS aerosol index are lower. In addition, the ability of the sensor to discriminate between different aerosol types is evaluated. Moreover, the estimates of the aerosol properties are used for atmospheric correction of the top-of-atmosphere reflectance. The AATSR surface reflectances are compared with the MODIS bidirectional reflectance distribution function/Albedo and MISR surface products and are shown to correspond with root-mean-square errors of 0.03 and 0.06 or better, respectively. The retrieval method is applied on an image basis resulting in an image of surface reflectance and a separate map of AOD. A map of AOD at 550 nm covering the Sahel and southern Sahara region is presented to demonstrate operation at regional and potentially global scales

Aerosol variability over Thessaloniki using ground based remote sensing observations and the TOMS aerosol index

The main aim of this work is to assess the performance of the Total Ozone Mapping Spectrometer (TOMS) on board the Earth Probe satellite aerosol index (AI) version 8.0 retrieved from the daily measurements of the TOMS instrument as an indicator of the presence of absorbing aerosols in the atmosphere. The analysis is carried out over the region of Northern Greece, an area exposed to various aerosol types from different sources. The aerosol optical depth (AOD) measured by a Brewer spectroradiometer situated in the centre of the city of Thessaloniki, at 40.6°N, 22.9°E, was employed as a measure of the aerosol loading in the atmosphere during the Earth Probe overpass. Discrete aerosol episodes that affect the area, such as biomass burning and Saharan dust events, have been isolated and studied in order to assess the effectiveness of using the TOMS AI in this highly complex atmospheric environment. The yearly values for the AOD measured at 355 nm range from 0.03 to 1.97 with a mean of 0.58±0.32 and for the AI from −1.67 to 3.06, with a mean of 0.22±0.73. This wide range of values results from the co-existence of urban, continental, marine and dust aerosols over Thessaloniki, a fact that makes it complicated to segregate optical effects on the observed radiation depending on different aerosol types. A total of 223 biomass burning events that affected Thessaloniki showed a correlation of 0.67 between the AOD and AI values whereas a correlation of 0.57 was deduced for the 37 cases of Saharan dust loading. A cluster analysis on the back-trajectories was performed in order to study the origins of the air masses over Thessaloniki, which permitted that the optical depth and AI were analysed depending on the possible source of the aerosols. The highest AOD values coupled with the highest AI values were seen for trajectories that transport air from the Saharan desert over Thessaloniki and those that bring polluted air from Eastern Europe and the Balkan regions. Even though some deductions were made vis-à-vis the origin and importance of different aerosol types over the city corroborating the usefulness of the AI in climatological or global climate studies, auxiliary information is essential for studying in detail the effects of the atmospheric aerosol loading over a local point of interest.

Significance of atmospheric inputs of calcium over the southwestern Mediterranean region: High mountain lakes as tools for detection

We quantified dry and wet atmospheric deposition of calcium over the southwest Mediterranean region and we assessed its impact on calcium dynamics of two high mountain lakes differing in morphometry and catchment characteristics. Atmospheric deposition of Ca averaged 40 mmol m−2 yr−1, and it showed a seasonal pattern similar to that reported for Saharan dust export to the Mediterranean region, with maxima during spring and summer. Ca enrichment from nonmarine sources was significantly related to the TOMS (Total Ozone Mapping Spectrometer) aerosol index. Atmospheric inputs significantly affected Ca concentration of the selected lakes, which do not presumably receive significant Ca inputs from weathering. The intensity of the effect depended on their corresponding sensitivities to evaporation. Total atmospheric inputs of Ca to each study lake catchment (11300 and 3100 moles) were enough to explain the lake Ca content (5400 and 111 moles, respectively). The results obtained in this study reveal that atmospheric inputs, particularly Saharan dust deposition, may be a significant source of calcium to remote mountain lakes.

Synoptics of dust transportation days from Africa toward Italy and central Europe

The mean synoptic situation associated with dust outbreaks from the Sahara into the central Mediterranean was examined on a daily basis for the month of July from 1979 to 1992. Composite patterns of wind, geopotential heights, and temperature for dusty days versus those for all days were analyzed. Dusty days were defined as days with the Total Ozone Mapping Spectrometer Aerosol Index (TOMS‐AI) in the area around the Apennine peninsula (36°N–46°N, 10°E–18°E) equal to or greater than their monthly average plus 1 standard deviation. It was found that the strength and position of two essential features of the circulation patterns, such as the trough emanating southward from the Icelandic low and the eastern cell of the subtropical high, are the governing factors in making suitable flows for the Saharan dust transportation toward Italy. The deep, well‐developed trough near the Atlantic coasts of Europe and Africa, penetrating well to the south, and the strong eastern cell of the subtropical high situated to the northeast from North Africa near the Mediterranean coast, cause strong south‐southwestern flows with the potential to carry dust northward into the Mediterranean. In extreme cases the dust can reach Europe north of the Alps and even northern Europe, reaching the shores of the Baltic. These warm flows, accompanied by high dust load, also cause considerable warming in the central Mediterranean region of the order of 6–8 K at 700 hPa. Alternatively, the weak western trough and the weak eastern subtropical cell cause westerlies, which are inconsistent with the Mediterranean dust intrusions. Analysis of the extreme intrusion cases in July 1988, based on TOMS‐AI data, and several others in July 2001–2003, based on lidar measurements in Rome, demonstrates the synoptic situation that allows the Saharan dust to reach Italy.

Quality, compatibility, and synergy analyses of global aerosol products derived from the advanced very high resolution radiometer and Total Ozone Mapping Spectrometer

A number of global aerosol products of varying quality, strengths, and weaknesses have been generated. Presented here are synthetic analyses with regard to the quality, compatibility, and synergy of two long‐term global (1983–2000) aerosol products derived from the advanced very high resolution radiometer (AVHRR) and the Total Ozone Mapping Spectrometer (TOMS). Four essential aerosol parameters, namely, aerosol optical thickness (AOT) from AVHRR under the Global Aerosol Climatology Project (GACP), TOMS AOT, Ångström exponent (AE) from AVHRR, and TOMS aerosol index (AI) are analyzed together with various ancillary data sets on meteorological fields, ocean color, and ground‐based AOT measurements. While the two satellite products reveal some common features, significant discrepancies exist. Reflectances measured at ultraviolet and visible wavelengths from the two sensors are incompatible in terms of the magnitude of AE computed from AOT derived from the two channels. The spatial distributions of the aerosol products from AVHRR and TOMS are complimentary in revealing different aspects of aerosol characteristics. In‐depth analyses were carried out over several regions under the influence of different types of aerosols such as biomass burning, dust, sea salt, air pollution, and their mixtures. A classification algorithm was developed to identify dominant types of aerosols around the globe using aerosol products from the two instruments. Aerosol type information is used to develop and apply relationships between the AVHRR AOT and the TOMS AOT. The latter was used to extend the AOT at 0.55 μm over land around the globe. Comparisons of monthly mean AOTs with AERONET monthly mean AOTs showed a general agreement to within an estimated error range of ±0.08 ± 0.20τ. Finally, a comparison between the estimated AOT with Moderate Resolution Imaging Spectroradiometer (MODIS) AOT over land showed good agreement in terms of magnitude and seasonality, suggesting a means of bridging past and current AOT estimations.

Characterization of east Asian dust outbreaks in the spring of 2001 using ground‐based and satellite data

This study presents a detailed examination of east Asian dust events during March–April of 2001, by combining satellite multisensor observation (Total Ozone Mapping Spectrometer (TOMS), Moderate‐Resolution Imaging Spectroradiometer (MODIS), and Sea‐Viewing Wide Field‐of‐View Sensor (SeaWiFS)) meteorological data from weather stations in China and Mongolia and the Pennsylania State University/National Center for Atmospheric Research Mesoscale Modeling System (MM5) driven by the National Centers for Environmental Prediction Reanalysis data. The main goal is to determine the extent to which the routine surface meteorological observations (including visibility) and satellite data can be used to characterize the spatiotemporal distribution of dust plumes at a range of scales. We also examine the potential of meteorological time series for constraining the dust emission schemes used in aerosol transport models. Thirty‐five dust events were identified in the source region during March and April of 2001 and characterized on a case‐by‐case basis. The midrange transport routes were reconstructed on the basis of visibility observations and observed and MM5‐predicted winds with further validation against satellite data. We demonstrate that the combination of visibility data, TOMS aerosol index, MODIS aerosol optical depth over the land, and a qualitative analysis of MODIS and SeaWiFS imagery enables us to constrain the regions of origin of dust outbreaks and midrange transport, though various limitations of individual data sets were revealed in detecting dust over the land. Only two long‐range transport episodes were found. The transport routes and coverage of these dust episodes were reconstructed by using MODIS aerosol optical depth and TOMS aerosol index. Our analysis reveals that over the oceans the presence of persistent clouds poses a main problem in identifying the regions affected by dust transport, so only partial reconstruction of dust transport routes reaching the west coast of the United States was possible.

Tropical tropospheric ozone morphology and seasonality seen in satellite and in situ measurements and model calculations

An important issue in satellite remote sensing techniques for retrieving tropical tropospheric ozone is understanding the cause of the disagreement between ozone derived from satellite residual‐based methods and the precursor distributions seen in both the fire count distribution and the Measurements Of Pollution In The Troposphere (MOPITT) CO distribution over northern tropical Atlantic and Africa in boreal winter and spring. This discrepancy has been called the Northern Atlantic paradox; however, it actually extends eastward all the way to Indonesia. We define the disagreement as the northern tropical paradox. We employ the scan angle method (SAM) to solve the paradox. This algorithm takes advantage of the difference in the Total Ozone Mapping Spectrometer (TOMS) retrieval information between nadir and high viewing angles. The averaging kernel for this difference exhibits a broad maximum centered at ∼5 km in the troposphere and thereby can be used to estimate tropospheric ozone information. The seasonal distribution of tropospheric ozone derived from the SAM algorithm shows remarkably good agreement with fire counts from Along Track Scanning Radiometer (ATSR), CO from MOPITT, TOMS aerosol index, and ozone distribution from the GEOS‐CHEM model in four seasons over the tropics. In meridional distribution, all of these products clearly reveal the seasonal oscillation between northern tropical Africa in boreal winter and over southern tropical Africa in boreal summer. The residual‐based methods (TOR, CCD, CCP, and modified residual), however, always show the ozone maximum over the southern Atlantic off the coast of southwest Africa. A further comparison with the in situ measurements from the Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) campaign at three locations over the northern tropics, Abidjan (5°N, 4°W), Madras (13°N, 80°E), and Bangkok (14°N, 101°E), supports our results. The seasonality of ozone from the SAM and the model, which shows the ozone maximum in boreal summer and the minimum in boreal winter, is in accordance with the MOZAIC measurements. However, the seasonality of the RBMs does not agree with the seasonality of in situ measurements. We conclude that the northern tropical paradox does not actually exist.

Comparison of ground‐based and Total Ozone Mapping Spectrometer erythemal UV doses at the island of Lampedusa in the period 1998–2003: Role of tropospheric aerosols

The Total Ozone Mapping Spectrometer (TOMS) has the longest time series of globally distributed estimates of UV irradiance at the Earth's surface. The proper interpretation of TOMS estimated irradiances relies on well‐calibrated and well‐maintained spectrometers at the Earth's surface. In this study, daily erythemal irradiances measured by a Brewer spectrophotometer at the island of Lampedusa (35.5°N, 12.6°E), in the Mediterranean are compared with TOMS observations in the period January 1998 to August 2003. The comparison, also because of the peculiar conditions at Lampedusa, a very good site for ground‐based validation of satellite observations, allows us to recognize how the space‐borne observations are influenced by the presence of atmospheric aerosols. Two TOMS data sets, derived applying different algorithms to retrieve ozone and UV irradiance from the backscattered radiance, are used in this study: Version 7 (V7) and the recently developed version 8 (V8), which uses new climatologies for ozone and temperature profiles and accounts for the attenuation by tropospheric aerosols through the aerosol index (AI). As shown in previous studies performed with V7 TOMS data, satellite‐derived erythemal doses systematically overestimate ground‐based measurements, mainly because of uncorrected absorption by aerosols in the troposphere. The bias between the TOMS and Brewer doses for all‐sky conditions is (9.4 ± 19.8)% for V7 and (7.3 ± 20.0)% for V8 and decreases to (5.6 ± 8.0)% for V7 and (3.4 ± 8.4)% for V8 for the cloud‐free cases. The large standard deviations for all‐sky conditions are due to nonhomogeneity in the cloud cover within the sensor field of view, while those for cloud‐free days are caused by the large aerosol variability occurring at Lampedusa. The biases for cloud‐free days have been related to differences in the TOMS AI UV attenuation algorithm and to the aerosol optical depth (AOD) at 415.6 nm measured with a Sun photometer at Lampedusa since 2001. The mean bias between the V7 TOMS and Brewer doses progressively increases with AI and AOD at 415.6 nm, from ± 3% for low AI and AOD up to 21% for 1.5 ≤ AI < 2.5 and 0.5 ≤ AOD < 0.6. The bias calculated with V8 data set varies between +6% for 0 ≤ AI < 1 and about −8% for 4 ≤ AI < 5, well within the respective uncertainties of the Brewer and TOMS measurements. TOMS V8 data show a smaller dependency on the aerosol absorption, indicating that the implemented corrections produce more reliable estimated doses. For very low aerosol loading (AOD at 415.6 nm below 0.2), the TOMS‐to‐Brewer erythemal dose ratio, both for V7 and V8, is approximately 1, indicating that the radiometric calibration of the Brewer instrument is consistent with the TOMS estimated irradiances from derived ozone and Rayleigh scattering attenuation.

Numerical study of Asian dust transport during the springtime of 2001 simulated with the Chemical Weather Forecasting System (CFORS) model

The regional‐scale aerosol transport model Chemical Weather Forecasting System (CFORS) is used for analysis of large‐scale dust phenomena during the Asian Pacific Regional Characterization Experiment (ACE‐Asia) intensive observation. Dust modeling results are examined with the surface weather reports, satellite‐derived dust index (Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI)), Mie‐scattering lidar observation, and surface aerosol observations. The CFORS dust results are shown to accurately reproduce many of the important observed features. Model analysis shows that the simulated dust vertical loading correlates well with TOMS AI and that the dust loading is transported with the meandering of the synoptic‐scale temperature field at the 500‐hPa level. Quantitative examination of aerosol optical depth shows that model predictions are within 20% difference of the lidar observations for the major dust episodes. The structure of the ACE‐Asia Perfect Dust Storm, which occurred in early April, is clarified with the help of the CFORS model analysis. This storm consisted of two boundary layer components and one elevated dust (>6‐km height) feature (resulting from the movement of two large low‐pressure systems). Time variation of the CFORS dust fields shows the correct onset timing of the elevated dust for each observation site, but the model results tend to overpredict dust concentrations at lower latitude sites. The horizontal transport flux at 130°E longitude is examined, and the overall dust transport flux at 130°E during March–April is evaluated to be 55 Tg.

Use of TOMS data to correct the saharan dust effects on SST retrievals from satellite

High loads of atmospheric aerosols introduce large errors in satellite-derived sea surface temperature (SST) retrievals. Airborne plumes of desert dust from North Africa are the most evident and persistent and cover large areas of the tropical Atlantic Ocean. We propose a methodology to correct for Saharan dust effects on sea surface temperatures derived from the AVHRR sensor. This method links SST errors in AVHRR estimates with concentrations of absorbing atmospheric aerosols as estimated by the Earth Probe Total Ozone Mapping Spectrometer (TOMS) Aerosol Index. Errors in the SST algorithm increase with increasing aerosol index estimates. To avoid these errors a correction term based on the TOMS aerosol index is incorporated to the AVHRR SST algorithm.

Empirical TOMS index for dust aerosol: Applications to model validation and source characterization

An empirical relation is developed to express the Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) for the case of dust plumes, as an explicit function of four physical quantities: the single scattering albedo, optical thickness, altitude of the plume and surface pressure. This relation allows sensitivity analysis of the TOMS AI with physical properties, quantitative comparison with dust model results and physical analysis of dust sources, without the necessity of cumbersome radiative calculation. Two applications are presented: (1) the case study of a dust storm over the North Atlantic in March 1988, and (2) the characterization of 13 major dust sources. The first application shows that simulated dust distribution can be quantitatively compared to TOMS AI on a daily basis and over regions where dust is the dominant aerosol. The second application necessitates to further parameterize the relation by replacing the optical thickness and the altitude of the plume by meteorological variables. The advantage is that surface meteorological fields are easily available globally and for decades but the formulation only applies to dust sources. The daily, seasonal and interannual variability of the parameterized index over major dust sources reproduces correctly the variability of the observed TOMS AI. The correlation between these two indices is used to determine the surface characteristics and physical properties of dust aerosol over the sources.

Atmospheric heating due to carbonaceous aerosol in northern Australia—confidence limits based on TOMS aerosol index and sun-photometer data

The aerosol index (AI) derived from backscattered UV radiances measured by the total ozone mapping spectrometer (TOMS) provides global coverage spanning nearly 20 years. Published maps of significant global sources of UV-absorbing aerosol produced from AI do not include northern Australia, despite the extensive grass fires that persist throughout the dry season, a result that could be interpreted to mean that radiative heating by smoke in northern Australia is not significant. In this paper, we show that such is not the case. The radiative heating is intense, persists throughout most of the dry season, and is likely to moderate the local climate. Numerical simulations to determine confidence limits for radiative heating based solely on AI data show that large uncertainties remain, because AI does not characterize either the vertical distribution or optical properties of aerosol uniquely. However, when AI is combined with sun-photometer observations of aerosol optical depth (AOD) at Jabiru in Kakadu National Park, the uncertainty is reduced markedly. Analysis of the combined data sets shows that moderate amounts of aerosol (with AOD≈0.5) persist throughout September and October. The associated radiative heating cannot be neglected, even in comparison with the heating produced by water vapour. The dominant sources of uncertainty, namely, the single-scattering albedo and the vertical distribution of the aerosol, are quantified. Simulations show that the uncertainty may be reduced significantly if sun-photometer and AI data are analyzed in conjunction with LIDAR data to determine the vertical distribution of aerosol.

Seasonal, intraseasonal, and interannual variability of global land fires and their effects on atmospheric aerosol distribution

In order to understand the variability of global land fires and their effects on the distribution of atmospheric aerosols, statistical methods were applied to the Tropical Rainfall Measuring Mission (TRMM) fire products as well as the Total Ozone Mapping Spectrometer (TOMS) aerosol index products for a period of 4 years from January 1998 to December 2001. The fire data in this period manifested a strong annual cycle of land fires in Southeast Asia with a peak in March and in Africa and North and South America with a peak in August. The data also indicated interannual variations in Indonesia and Central America associated with the 1998–1999 El Niño‐Southern Oscillation cycle. The variability of global atmospheric aerosol is consistent with the fire variations over these regions. However, in southwestern Australia, intense fires were recorded in TRMM fire data, but no smoke was observed in the TOMS aerosol product. Excluding the Australian region, the correlation between fire count and TOMS aerosol index is about 0.55 for fire pixels. Empirical orthogonal function analysis (EOF) and singular spectrum analysis methods were used to analyze the TRMM Science Data and Information System pentad fire composite data and TOMS pentad aerosol index data for this 4 year period. The EOF analyses showed contrast between the Northern and Southern Hemispheres and also intercontinental transitions in Africa and America. These analyses also identified 25–60 day intraseasonal oscillations that were superimposed on the annual cycles of both fire and aerosol data. The intraseasonal variability of fires showed a similarity of Madden‐Julian oscillation mode.