Precipitation Radar Data Research Articles

Next generation of NOAA/NESDIS TMI, SSM/I, and AMSR‐E microwave land rainfall algorithms

Revised versions of previous passive microwave land rainfall algorithms are developed for the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), the Special Sensor Microwave/Imager (SSM/I), and the new Advanced Microwave Sounding Radiometer‐Earth Observing System (EOS) (AMSR‐E). The relationships between rainfall rate and 85 GHz brightness temperature are recalibrated with respect to previous algorithms using collocated TMI and TRMM Precipitation Radar (PR) data. Another new feature is a procedure to estimate the probability of convective rainfall, as convective/stratiform classification can reduce the ambiguity of possible rainfall rates for a given brightness temperature. These modifications essentially eliminate the global high bias found in studies [e.g., McCollum et al., 2000; Kummerow et al., 2001] of previous versions of the SSM/I and TMI algorithms. However, many regional and seasonal biases still exist, and these are identified. The applicability of the new features to the other microwave sensors is studied using SSM/I data, and a correction is developed to account for the differences in footprint resolution between the TMI and SSM/I. The AMSR‐E algorithm is the same as the TMI, as the footprint resolutions and frequencies of these instruments are very similar. The TMI algorithm will be used in the land portion of the official version 6 TMI instantaneous rainfall rate product, to be released in 2003, while the AMSR algorithm will be used in a similar manner for future AMSR‐E products.

Seasonal and year‐to‐year variations of rainfall in the Sahara desert region based on TRMM PR data

Using TRMM (Tropical Rainfall Measuring Mission) precipitation radar data and NCEP reanalysis data, this paper investigates seasonal and year‐to‐year variations of rainfall over the Sahara desert (20°–30°N, 10°W–30°E) from 1998 to 2001. Most rainfall occurs in the northern (southern) part from October to April (July to September). From May to June, precipitation occurs in both areas. Seasonal migration of the main rainfall area results from changes of rainfall types associated with the change of zonal wind and specific humidity in Northern Africa. While the mid‐latitude westerly at 200 hPa is dominant when rainfall occurs in the northern part, the African Easterly Jet (AEJ) at 600 hPa and the lower layer moisture affect rainfall in the southern part. Year‐to‐year rainfall amount variations are also related to zonal wind changes, such as southward migration of the westerly and northward migration of the AEJ.

A GIS methodology for the analysis of weather radar precipitation data

A GIS multi-component module was developed within the ArcView GIS environment for processing and analysing weather radar precipitation data. The module is capable of: (a) reading geo-reference radar data and comparing it with rain-gauge network data, (b) estimating the kinematics of rainfall patterns, such as the storm speed and direction, and (c) accumulating radar-derived rainfall depths. By bringing the spatial capabilities of GIS to bear this module can accurately locate rainfall on the ground and can overlay the animated storm on different geographical features of the study area, making the exploration of the storm's kinematic characteristics obtained from radar data relatively simple. A case study in the City of Hamilton in Ontario, Canada is used to demonstrate the functionality of the module. Radar comparison with rain gauge data revealed an underestimation of the classical Marshal & Palmer Z–R relation to rainfall rate.

Validation of TRMM Radar Rainfall Data over Major Climatic Regions in Africa

Abstract The Global Precipitation Climatology Center global-precipitation-analyses rain gauge data have been used to validate the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) data over the major climatic regions in Africa. The threshold-matched precipitation index and the TRMM-and-other-sources “best-estimate” data (3B43) have also been compared with rain gauge data and with the TRMM PR rainfall product. In the 36-month climatological assessment of the satellite products at a grid spacing of 1.0°, continental Africa has been categorized into five distinct climatic regions: arid, semiarid, savanna, tropical wet, and the South Atlantic Ocean. Zonal mean analysis shows that TRMM PR has a large overestimation in the tropical-rain-forest region of Africa in December–January–February and in March–April–May. The bias is minimized in June–July–August and September–October–November. Bias is generally high for all algorithms in the dry seasons when rainfall is minimal but is less pronounced i...

A Surface Reference Technique for Airborne Doppler Radar Measurements in Hurricanes

Abstract The operational algorithm for rainfall retrieval from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar data requires a measurement of the path-integrated attenuation (PIA) as a constraint. This constraint is derived via the surface reference technique, whereby a measurement of the ocean surface in a raining area is compared with the ocean surface backscatter in a neighboring clear area. This method assumes that the surface backscatter difference is due only to the presence of rain, although variation in surface winds could also cause differences in the reference and rain measurements. An alternative surface reference method is to use a measurement of the surface winds and a backscatter model to predict the rain-free, or reference, cross section. Such an approach is developed here for airborne Doppler radar measurements in hurricanes. This approach provides an independent measurement of the reference backscatter, which is compared with the standard clear-air reference. The mean d...

Precipitation Characteristics in Mid-Latitude East Asia as Observed by TRMM PR and TMI

Precipitation radar and microwave radiometer data from the Tropical Rainfall Measuring Mission (TRMM) satellite during the spring and summer months of 1998 are used to study the precipitation characteristics in the mid-latitude East Asia region (20°-40°N, 100°-140°E), with particular emphasis on comparing the differences between stratiform and convective rains, and between rains during spring and summer. The characteristics in the mid-latitude are also compared with those in the tropics. The two-season mean results for the mid-latitudes show that the mean rainfall rate for stratiform clouds is ∼2 mm h-1, at least 6 times lower than its convective counterpart. The mean convective rainfall rate is higher over land than over ocean, and higher in the mid-latitude than in the tropics. Generally, convective clouds generate more rain total for both mid-latitudes and tropics although they cover less area than stratiform clouds. Comparing between mid-latitude and tropical regions, the contribution of stratiform rains is larger in the mid-latitudes than in the tropics. There are distinct differences between stratiform and convective precipitation profiles, as well as noticeable seasonal variations of these profiles. The mean vertical profiles showed that stratiform rains have a quasi-constant rainfall rate below freezing level and a sharp drop-off above. Convective profiles, on the other hand, often have a maximum rainfall rate somewhere below the freezing level. Above the freezing level, precipitation layer for convective rains is thicker than for stratiform rains. For convective rains, significant differences are found between profiles over land and ocean, with a significant deeper layer for land convections given the same surface rainfall rate. Consistently, microwave scattering signature over land, expressed by polarization-corrected temperature at 85 GHz, is nearly twice as strong as that over ocean for the same surface rainfall rate. Precipitation profiles are similar in shape and depth between mid-latitude and tropical regions during summer when the freezing level heights are also similar between the two regions. However, compared to being no noticeable variation in the tropics during a year, there is a significant seasonal change for the precipitation profiles in mid-latitudes. The seasonal difference of precipitation profiles arises from the deeper precipitation layer in the summer than in the spring for a given surface rainfall rate, being in consistent with the seasonal variation of the freezing level height. This change in precipitation depth applies to both stratiform and convective rains, and to rains over both land and ocean. It should be mentioned that all the aforementioned results, except for the 85 GHz scattering signature, are derived from TRMM precipitation radar data.

Spatial and Seasonal Variation of Rain Profiles over Asia Observed by Spaceborne Precipitation Radar

Abstract The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) has made it possible for the first time to evaluate global characteristics of vertical structures of rainfall over monsoon Asia. This study is intended to depict features of seasonal variations of the vertical gradient of rainfall rate using TRMM PR data from 1998 to 2000. The features of downward decreasing (DD) or downward increasing (DI) rainfall rate in the lower part of the vertical profile are focused on. Horizontal maps were made showing decreasing/increasing characteristics in the vertical gradient of rainfall rate over Asia. The pattern showed a clear land–ocean contrast and had monthly variation as the monsoon progressed in Asia. The DD pattern migrated northward around the monsoon onset and withdrew southward in the retrogressing period. The seasonal march of the DD pattern was clear especially over the India subcontinent. The DD seemed to be bordering monsoon rainfall over India. Seasonal changes in characteristic...

Rainfall estimation from TOGA radar observations during LBA field campaign

The TRMM Large Scale Biosphere‐Atmosphere (LBA) experiment, conducted between January and February of 1999 in Southwest Amazon, deployed among other instruments NASA's C‐band Doppler radar (TOGA) and four dense rain gauge networks. This paper presents a procedure devised to derive surface rainfall rate estimates from combination of TOGA observations and the in situ rain gauge rainfall measurements. The spatial and temporal scales considered are 2 × 2 km2 grids of instantaneous to hourly rain accumulations. The procedure includes evaluation of TOGA calibration through comparisons with TRMM Precipitation Radar (PR) data and implementation of an optimal quantitative precipitation estimation (QPE) algorithm. Comparisons with PR indicated a 4‐dB calibration offset occurring in the later two thirds of the observation period. The implemented QPE algorithm applies a parameter that differentiates the Z‐R conversion in convective and stratiform regimes and a stochastic filtering approach for estimation of mean‐field bias on the basis of radar‐rain gauge comparisons at the hourly timescale. The calibration of the algorithm parameter values is formulated as a global optimization problem, which is solved by minimizing the radar‐rain gauge rainfall accumulation root‐mean‐square (rms) difference at the hourly timescale. A random resampling calibration/validation exercise is performed to evaluate the algorithm performance and its sensitivity to parameter values. Validation against gauges shows that the algorithm produces unbiased estimates with ∼57% relative RMS difference at the hourly scale. Comparison with S‐POL rain estimates showed good correlation (0.9) but some overestimation (9%). Rainfall products are used to derive rainfall statistics for two distinct meteorological low‐level wind regimes (easterly and westerly) that occurred during LBA. Finally, instantaneous rain estimates are compared against TRMM PR rainfall profiles for six coincident storm cases showing high correlation (0.9) and low (7%) systematic difference (PR overestimation).

TRMM Observations of Intraseasonal Variability in Convective Regimes over the Amazon

This study utilizes the Tropical Rainfall Measuring Mission (TRMM) satellite precipitation radar (PR), lightning imaging sensor (LIS), and passive microwave imager (TMI) data together with ground-based lightning data to investigate the vertical structure, lightning, and rainfall characteristics of Amazonian and subtropical South American convection for three separate wet seasons. These characteristics are partitioned as a function of 850mb zonal wind direction, motivated by observations collected during the 6-week TRMM‐Large-scale Biosphere‐ Atmosphere Experiment in Amazonia (LBA) field campaign. The TRMM‐LBA field campaign observations suggest that systematic variations in Amazonian convective vertical structure, lightning, and rainfall are all linked to bimodal variations in the low-level zonal wind (e.g., easterly and westerly regimes). The more spatially and temporally comprehensive TRMM dataset used in this study extends the TRMM‐LBA observations by examining regime variability in Amazonian and South American convective structure over a continental-scale domain. On a continental scale, patterns of east and west regime 850‐700-mb winds combined with LIS lightning flash densities suggest the presence of synoptic-scale controls [e.g., intrusion of extratropical frontal systems and interaction with the South Atlantic Convergence Zone (SACZ)] on regional-scale variability in convective vertical structure. TRMM PR, TMI, and ground-based lightning data suggest that regional variability in wetseason convective structure is most evident over the southern Amazon, Mato Grosso, Altiplano, southern Brazil, and eastern coastal regions of central and southern South America. Convective vertical structure, convective rainfall rates, and lightning activity are all more pronounced during easterly (westerly) regimes over the southern Amazon and Mato Grosso (Altiplano, and southern Brazil). Importantly, when considered with case study results from TRMM‐LBA, the systematic differences in convective structure that occur as a function of regime suggest that associated regime differences may exist in the vertical distribution of diabatic heating. Hence the discrimination of convective vertical structure ‘‘regimes’’ over parts of the Amazon and vicinity based on a resolved variable such as the 850‐700-mb zonal wind direction, while far from being perfect, may have important applications to the problems of cumulus parameterization, rainfall estimation, and retrievals of latent heating over the Amazon.

A Surface Wind Model–Based Method to Estimate Rain-Induced Radar Path Attenuation over Ocean

Abstract The rainfall retrieved using the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) depends on estimating the radar signal path-integrated attenuation using the surface reference technique (SRT). This technique assumes uniform ocean surface backscattering background at precipitation scale and attributes the difference in measured surface backscattering cross sections inside and outside of storms to path-integrated attenuation. Since surface wind is the major environmental variable that controls the strength of the ocean backscattering, it is very desirable to examine the impact of surface wind variation on the retrieved attenuation. To this end, we examined the feasibility of retrieving ocean surface winds from TRMM PR data for the benefit of the surface reference technique. A geophysical model function, a forward model, is developed based on ocean surface wind speed retrieved from TRMM Microwave Imager (TMI) data. A fieldwise wind-retrieval procedure, an inverse model, is formul...

Characteristics of the Mirror Image of Precipitation Observed by the TRMM Precipitation Radar

A mirror image is a virtual image of precipitation from below the ocean surface when an airborne or a spaceborne radar is used to view rainfall over the ocean. It is due to a reflection of energy from the sea surface tothe precipitation and back to the radar via a second reflection at the sea surface. The mirror image characteristics were investigated using Tropical Rainfall Measuring Mission (TRMM) precipitation radar data and the following was found. 1) The radar can detect the mirror image clearly over the ocean. 2) The mirror image echo corresponds well to the direct rain echo at nadir and near-nadir incidence angles. 3) In a weak rain region, the mirror echo intensity is nearly proportional to the direct echo power except near the radar noise level. 4) In the strong rain region, rain attenuation effects clearly appear. 5) The ratio of the mirror echo power to the direct echo power is affected by the rain attenuation, which varies with the brightband height and the range of the target rain from surface. Further, a simple simulation was performed in order to confirm the above characteristics. The signal fluctuation, noise contamination, rain attenuation, and surface cross section are taken into account in the simulation. The results of simulation confirmed the observation results.

Characteristics of the 1998 Summer Monsoon Onset over the Northern South China Sea.

Observations from the May–June 1998 South China Sea Monsoon Experiment (SCSMEX) have been used to determine the characteristics of the onset of the summer monsoon over the northern South China Sea (SCS). The onset occurred in mid-May with a rapid increase in deep convection over a weekto-ten-day period, followed by a ~ten-day break, and then a resumption of deep convection for a week-toten-day period in early June. The temporal and spatial variabilities of rainfall rates from the atmospheric moisture budget, satellite, and model estimates generally agree well, although the mean rainfall rate from the models for the 47-day Intensive Observing Period (IOP) is about 25% greater than the other estimates. The SST gradually increased over the northern SCS during the IOP, interrupted by slight cooling following monsoon onset until early June when the warming resumed. Surface sensible and latent heat fluxes increased after onset, but then decreased in June as a result of warm, moist air advecting over cooler water near the south China coast. The mean apparent heat source Q1 during convective periods resembled that determined for other tropical oceanic regions with a peak near 400 hPa. The apparent moisture sink Q2 also resembled profiles for other tropical regions, except for larger values below 900 hPa. The heating and moistening rates and vertical eddy flux of total heat during the early-June active period were greater than those observed during the May monsoon onset active period, indicating more vigorous deep convection as the monsoon ensued, a finding supported by Tropical Rainfall Measuring Mission (TRMM) precipitation radar data.

TRMM Precipitation Radar and Microwave Imager Observations of Convective and Stratiform Rain over Land and their Theoretical Implications.

Observations of brightness temperature, Tb, made over land regions by the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer are analyzed with the help of nearly simultaneous measurements of the vertical profiles of reflectivity factor, Z, made by the Precipitation Radar (PR) onboard the TRMM satellite. Furthermore, this analysis is done separately over convective and stratiform rain regions. This examination reveals a clear relationship between TMI and PR data. Possible explanation for this relationship is explored with the help of radiative transfer calculations. With this approach, we demonstrate that the 85 GHz observations of TMI can be simulated crudely from the observations of Z. However, the 37 and 19 GHz observations are not as well simulated, possibly because of horizontal non-uniformity in the hydrometeor distribution in the broad footprints of these channels and contamination introduced by land-surface emissivity. On the other hand, from TMI and PR observations, we find that the brightness temperature difference (T19-T37) minimizes these sources of error. Our simulations of (T19-T37) over convective rain regions are in reasonable agreement with this finding. This investigation indicates that the TMI 85 GHz channel yields the best information about rain over tropical land, because it has minimal surface contamination, strong extinction, and a fine footprint. The brightness temperature difference (T19-T37) can supplement the information given by the 85 GHz channel.

Evolution of the Large Scale Circulation, Cloud Structure and Regional Water Cycle Associated with the South China Sea Monsoon during May-June, 1998.

In this paper, changes in the large-scale circulation, cloud structures and regional water cycle associated with the evolution of the South China Sea (SCS) monsoon in May-June 1998 were investigated using data from the Tropical Rainfall Measuring Mission (TRMM) and field data from the South China Sea Monsoon Experiment (SCSMEX). Results showed that both tropical and extratropical processes strongly influenced the onset and evolution of the SCS monsoon. Prior to the onset of the SCS monsoon, enhanced convective activities associated with the Madden and Julian Oscillation were detected over the Indian Ocean, and the SCS was under the influence of the West Pacific Anticyclone (WPA) with prevailing low level easterlies and suppressed convection. Establishment of low-level westerlies across Indo-China, following the development of a Bay of Bengal depression played an important role in building up convective available potential energy over the SCS. The onset of SCS monsoon appeared to be triggered by the equatorward penetration of extratropical frontal system, which was established over the coastal region of southern China and Taiwan in early May. Convective activities over the SCS were found to vary inversely with those over the Yangtze River Valley (YRV). Analysis of TRMM microwave and precipitation radar data revealed that during the onset phase, convection over the northern SCS consisted of squall-type rain cell embedded in meso-scale complexes similar to extratropical systems. The radar Z-factor intensity indicated that SCS clouds possessed a bimodal distribution, with a pronounced signal (less than 30dBz) at a height of 2-3 km, and another one (less than 25 dBz) at the 8-10 km level, separated by a well-defined melting level indicated by a bright band at around 5-km level. The stratiform-to-convective cloud ratio was approximately 1:1 in the pre-onset phase, but increased to 5:1 in the active phase. Regional water budget calculations indicated that during the active phase, the SCS was a strong sink (E-P much less than 0) of atmospheric moisture, with the primary source of moisture coming from regions further west over Indo-China and the eastern Indian Ocean. Before onset and during the break, the SCS was a moisture source (E-P greater than ) to the overlying atmosphere. In particular, the SCS provided the bulk of moisture to the torrential rain over the YRV in mid-June 1998.

GIS and Distributed Watershed Models. I: Data Coverages and Sources

The increasing proliferation of spatial data, geographic information systems (GIS), and models for hydrologic applications provide many new investigation opportunities but also present a number of challenges for the uninitiated water resources practitioner. This two-part paper is intended for the practicing engineer who wants to expand into the arena of spatial data and distributed watershed modeling. It provides an integrated overview of the multiple facets of data-GIS-modeling issues and a source of background information for selection and application of GIS in watershed modeling. This first paper addresses selected spatial data issues, data structures and projections, data sources, and information on data resolution and uncertainties. Spatial data that are covered include digital elevation data, stream and drainage data, soil data, digital orthophoto data, remotely sensed data, and radar precipitation data. The focus is on data and issues that are common to many data-GIS- modeling applications. The second paper presents issues on and examples of GIS and hydrologic models and provides recommendations with respect to organization and implementation of the integrated use of spatial data, GIS, and distributed watershed models.

The Variability of Tropical Precipitation Profiles and Its Impact on Microwave Brightness Temperatures as Inferred from TRMM Data

Precipitation radar and microwave radiometer data collected by the Tropical Rainfall Measuring Mission (TRMM) satellite are used to study the variability of precipitation profiles and the relationship between precipitation profile and microwave brightness temperature. The variability has been examined using empirical orthogonal function (EOF) analysis and microwave emission and scattering signatures. Precipitation profiles are divided into three groups according to emission signatures at 19.4 GHz and three groups according to scattering signatures at 85.5 GHz. For stratiform rain, the differences of vertical precipitation profiles among these groups are small and are mainly seen in the slope of profiles below the freezing level. However, clear differences in vertical precipitation profiles can be found among the deep-convective rain groups. The maximum rainfall rate occurs at a considerably lower altitude when low liquid-emission or low ice-scattering signatures are observed. When emission or scattering signatures are high, precipitation profiles peak near the freezing level, a feature that is similar to the one in stratiform precipitation profiles. The three patterns of the vertical profiles derived from microwave signatures are very similar to the three patterns derived by EOF analysis. This similarity suggests that the three patterns derived by microwave signatures represent the most significant variability in vertical precipitation profiles. Results also show that, for the same near-surface rainfall rate, the pixel group with anomalously high microwave emission also shows anomalously high microwave scattering, and vice versa, suggesting that the liquid and ice water amounts in tropical rains are correlated over scales the size of a satellite pixel. It is also found that, for a given surface rainfall rate, the brightness-temperature differences among the pixel groups are large, highlighting the importance of vertical precipitation profile in determining upwelling microwave radiation and, therefore, the need to incorporate realistic precipitation profile information in rain retrieval algorithms.

Study and Tests of Improved Rain Estimates from the TRMM Precipitation Radar

Abstract Rain rate R estimation from the 2A-25 profiling algorithm of the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) is analyzed in two ways. Standard results from the operating version-5 algorithm are compared with those from the previous version 4. Also, various adjustments of the involved rain relationships in version 4 are explored, which leads to the proposal of two alternatives to the standard rain rate (Rstd-V4). The first one, (RN0), is based on N*0-scaled relations exploiting the concept of normalized Γ-shaped drop size distributions; the second one, (RkR), relies on using constant R–k instead of constant R–Z relation as in the standard, where Z is reflectivity and k is attenuation coefficient. Error analysis points out a lower sensitivity of the alternative estimates to errors in radar calibration, or initial relations, than the standard. Results from a set of PR data, over ocean and land, show that the version-4 alternatives, and version-5 standard (Rstd-V5), produce mo...

Regional Variability in Tropical Convection: Observations from TRMM

Abstract Observation of the vertical profile of precipitation over the global Tropics is a key objective of the Tropical Rainfall Measuring Mission (TRMM) because this information is central to obtaining vertical profiles of latent heating. This study combines both TRMM precipitation radar (PR) and Lightning Imaging Sensor (LIS) data to examine “wet-season” vertical structures of tropical precipitation across a broad spectrum of locations in the global Tropics. TRMM-PR reflectivity data (2A25 algorithm) were utilized to produce seasonal mean three-dimensional relative frequency histograms and precipitation ice water contents over grid boxes of approximately 5°–10° in latitude and longitude. The reflectivity histograms and ice water contents were then combined with LIS lightning flash densities and 2A25 mean rainfall rates to examine regional relationships between precipitation vertical structure, precipitation processes, and lightning production. Analysis of the reflectivity vertical structure histograms ...

Rainfall Estimation from a Combination of TRMM Precipitation Radar and GOES Multispectral Satellite Imagery through the Use of an Artificial Neural Network

This paper describes the development of a satellite precipitation algorithm designed to generate rainfall estimates at high spatial and temporal resolutions using a combination of Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) data and multispectral Geostationary Operational Environmental Satellite (GOES) imagery. Coincident PR measurements were matched with four-band GOES image data to form the training dataset for a neural network. Statistical information derived from multiple GOES pixels was matched with each precipitation measurement to incorporate information on cloud texture and rates of change into the estimation process. The neural network was trained for a region of Brazil and used to produce half-hourly precipitation estimates for the periods 8-31 January and 10-25 February 1999 at a spatial resolution of 0.12 degrees. These products were validated using PR and gauge data. Instantaneous precipitation estimates demonstrated correlations of ~0.47 with independent validation data, exceeding those of an optimized GOES Precipitation Index method locally calibrated using PR data. A combination of PR and GOES data thus may be used to generate precipitation estimates at high spatial and temporal resolutions with extensive spatial and temporal coverage, independent of any surface instrumentation.

TRMM satellite estimates of convective processes in central Africa during September, October, November 1998: Implications for elevated Atlantic tropospheric ozone

The recent launch of the Tropical Rainfall Measuring Mission (TRMM) allows for new understanding of convective processes in remote areas of Equatorial Africa. Time averaged rainfall statistics during September, October and November of 1998 for TRMM merged data and TRMM Precipitation Radar data are compared to long‐term averages. The TRMM precipitation radar data shows the highest convective rainfall rates and mean storm heights in October occurring west of the East African Highlands. This area is downstream of savanna fires and could serve as an important region for the vertical transport of pollutants, which are then transported westward in the upper troposphere contributing to the high ozone values over the Tropical eastern Atlantic ocean.