Interactive comment on “ A cautionary use of DCC as a solar calibration target : explaining the regional difference in DCC reflectivity

Introduction Conclusions References Tables Figures


Introduction
Vicarious calibrations for solar channels are particularly important for geostationary weather satellites that are not usually equipped with an onboard calibration system for the visible sensor, in order to assure the radiometric quality of satellite measurements.
There are a variety of vicarious calibration methods in this end using different targets such as bright desert targets (Govaerts and Clerici, 2004;Miesch et al., 2003;Chun et al., 2012;Chun and Sohn, 2014), cloud targets (Kim et al., 2013;Ham and Sohn, 2010;Doelling et al., 2010;Sohn et al., 2009), and moon targets (Cao et al., 2009;Barnes et al., 2004).Amongst different approaches the use of deep convective cloud a natural diffuser (Sohn et al., 2009;Doelling et al., 2013a, b;Stercks et al., 2013).Since DCCs are abundant throughout the tropical belt and seasons alike there should be excellent advantage that all different sensors onboard geostationary satellites may be calibrated using DCC targets.For this, however, underlying assumption is that DCCs have radiatively similar behaviors.
However, a recent study by Doelling et al. (2013a), based on an analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) solar channel measurements, reported that DCCs over the tropical western Pacific have lower reflectivity (or are darker) than DCCs over continental tropical regions such as Africa and South America.This suggests that simple adoption of DCC approach may result in erroneous calibration result.
In this study, with the goal of understanding why DCCs over the western Pacific show generally lower reflectivity in comparison with those over tropical African and South American regions, regional differences in optical properties of DCCs are examined using CloudSat Cloud Profile Radar (CPR) and Cloud Aerosol Lidar Infrared Pathfinder Satellite Observation (CALIPSO) measurements.From an intercomparison of the vertical structures of DCC optical properties, important elements causing regional differences in DCC reflectivity are identified.The obtained results may lead to a better understanding of the role of tropical DCCs in the use of DCC targets for the solar channel calibration.CloudSat carries an active sensor called CPR that measures vertical profiles of reflectivity due to atmospheric hydrometeors at 94 GHz.The CloudSat 2B-GEOPROF product provides radar reflectivity and cloud mask information for 125 height bins.Because a cloud mask value of 30 is considered to be a threshold ensuring cloud presence in a given layer (Mace et al., 2007), CloudSat profiles are selected for analysis if the cloud mask value is greater than 30.Beside the use of reflectivity profiles, CloudSat-retrieved cloud parameters are used.These include cloud water content and effective radius profiles obtained from CloudSat 2B-CWC-RVOD products whose pixel resolution is about 1.4 km (Wood, 2008).However, because CloudSatderived liquid water content and liquid effective radius are erroneous as the result of miscalculation of the attenuation by liquid cloud droplets (as of 21 Sept 2011, the CloudSat Data Processing Center listed on its website the "2B-CWC-RVOD 008 issue: radar forward model attenuation in liquid cloud," which is available online at http://www.cloudsat.cira.colostate.edu/dataIssue.php?prodid=6&pvid= 227&anomalyid=325230) and those problems were not yet corrected by the time to write this paper, only ice water content (IWC) and ice effective radius (R e ) profile data were used in this study to examine the reflectivity difference.Because the visible extinction coefficient (k ext ) is closely linked to the optical thickness and visible reflectivity observable at top of atmosphere (TOA), the k ext profile is estimated as follows (e.g., Lin and Rossow 1994;Ham and Sohn 2012): In Eq. ( 1), extinction efficiency (Q e ) is considered to be nearly equal to 2 in the visible range, and density of ice crystals (ρ i ) is fixed as a constant (i.e., 0.917 g m −3 ), as used in CloudSat retrieval.CALIPSO also carries an active sensor, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), beaming at 532 and 1064 nm wavelengths and sensitive to particles much smaller than those detectable by CloudSat.Because CloudSat misses the top portion of DCC composed of small ice crystals (Kahn et al., 2008), CALIPSO data are used for information on cloud properties above the CloudSat-detected upper boundary of the reflectivity profile.In this study, CALIPSO-derived cloud parameters such as extinction coefficient at 0.532 µm (Young and Vaughan 2009) and ice water content (Heymsfield et al., 2005) profiles (CALIPSO L2-05kmCPro, Edition 3.01) are analyzed.It is a 5 km average based on the average of 15 CALIOP FOV of 100 m laser shots.

Construction of collocation data
Collocated data from Aqua MODIS, CloudSat, and CALIPSO, which compose the A-train mission (Stephens et al., 2002;Parkinson 2003;Winker et al., 2003), are constructed.However, because of the different MODIS scan geometry, measuring a much wider region, nadir-viewing scenes of MODIS measurements are collocated with CloudSat and CALIPSO measurements in about a 1 km field of view.Collocation is carried out over the along-track of CloudSat by selecting the closest MODIS and CALIPSO pixels from a given CloudSat pixel.The combination of collocated CloudSat, CALIPSO, and MODIS data will provide us overall features of the physical/optical properties of DCCs, from which key factors contributing to the regional difference in DCC reflectivity can be examined.

Analysis domain and period
In order to examine the regionally different optical properties of DCCs, three analysis areas are selected (Fig. 1), i.e., continental Central Africa ( 20• N-20 • S, 0-40 Full January is chosen because it is the time of year when DCCs are frequently observed over all three analysis regions.

DCC data
The DCCs of interest in this study are defined as optically thick clouds with top heights reaching higher than 14 km associated with strong convection resulting in cold cloudtop temperatures.Because of such high-altitude cloud tops, TB 11 has often been used as a criterion determining the presence of DCCs.TB 11 thresholds ranging from 190-210 K have been used for different DCC-related study objectives (e.g., Aumann et al., 2007;Liu et al., 2007;Sohn et al., 2009).The sensitivity of the TB 11 threshold to measured visible radiance was tested by Doelling et al. (2013a), and the lowest radiances of DCCs, among the three selected regions of Fig. 1, were found over the western Pacific, especially when MODIS pixels of TB 11 < 205 K were chosen as DCCs.
In this study, the same TB 11 of 205 K is used as the threshold to determine DCCs.
To avoid DCC targets located near the cloud edge or DCCs related to small-scale cloud plumes, spatial homogeneity is applied to the distribution of TB 11 and Ref 0.6 .A selected pixel is identified as a DCC target if the 9 × 9 MODIS pixels (corresponding to about 10 km × 10 km) surrounding the CloudSat pixel show a SD of TB 11 of less than 1 K.The spatial homogeneity criterion is also applied for visible reflectivity.The pixel is selected if the SD of the Ref 0.6 from the surrounding 9×9 pixels normalized by the mean value is less than 0.03.Collocation targets are selected only if both criteria are satisfied.The confidence level of the collocation is enhanced by restricting the solar zenith angle (SZA) and satellite viewing zenith angle (VZA) to less than 40 • .Furthermore, only single-layered cloud, which can be determined from the vertical structure of CloudSat radar reflectivity, is retained in this DCC analysis.Introduction

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Full The total numbers of pixels passing the aforementioned criteria are 285, 687, and 2377 for Africa, South America, and the western Pacific region, respectively.The number of DCC pixels collected for each month is given in Table 1.Considering that the western Pacific domain size is about twice the size of the two land regions, DCCs are found to be more abundant over the western Pacific region compared to the two land regions.It is also interesting to note that the African domain seems to show a more fluctuating interannual pattern over the four-year period.

MODIS measurements
First, statistical distributions of selected DCC pixels are compared with one another for the three regions.In doing so, probability density functions (PDFs) of MODIS-measured TB 11 , Ref 0.6 , MODIS-derived COT, and R e are obtained and are presented in Fig. 2. PDFs for TB 11 (Fig. 2a) show generally decreasing frequency with decreasing temperature.The more fluctuating patterns found in the two land regions may be, in part, due to the relatively smaller sample size (shown in Table 1).Interestingly, extremely cold TB 11 (lower than 190 K) is found more frequently over the western Pacific (black solid line), although the total frequencies are very small (less than 3 % of the sample size).Consequently, warmer TB 11 appears to be more frequent (in percentage) over the land regions of Africa and South America.
Corresponding reflectivity distributions are shown in Fig. 2b.The western Pacific region shows a more widely distributed pattern, with a reflectivity peak around 0.98, compared to the two land regions.On the contrary, the two land regions exhibit patterns shifted to higher reflectivity, with a more dominant probability at a peak reflectivity of about 1.It is clear that DCCs found over the western Pacific are generally darker than those found over tropical Africa and South America; their mean values are 0.93, 0.98, and 0.98, respectively (Table 2).By combining these with the patterns noted Introduction

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Full in TB 11 distributions, the DCCs over the two tropical land regions can be characterized as clouds that show warmer cloud tops along with higher reflectivity compared to those in the western Pacific: 199.6 K (Africa) and 200.2K (South America) vs. 198.8K (western Pacific) (Table 2).These results are consistent with the findings of Doelling et al. (2013a).
PDFs of MODIS-derived COT and R e are given in Fig. 2c and d, respectively.Because the MODIS cloud algorithm only provides COT up to 100 even if clouds are thought to be optically thicker than 100 and because DCCs having COT = 100 occupy 69.5, 71.5 %, and 49.0 % of the DCCs for Africa, South America, and the western Pacific domains, respectively, the dominant portion of PDFs should be located near COT = 100.Thus, separate plots are made for COT < 100 and for COT > 90.As shown in Fig. 2b, the majority of DCCs over the two land regions show DCCs with reflectivity (i.e.bidirectional reflectance based on the Lambertian assumption) higher than or equal to 1.In contrast, about half of the DCC samples over the western Pacific show COT > 100, indicating that the DCCs found over the western Pacific are optically thinner than those of the two land counterparts.Furthermore, considering that remaining 50 % of DCC pixels are more evenly distributed throughout the covered COT range, the DCCs determined by applying only the criteria of TB 11 = 205 K may have contained more optically thinner convective/anvil-type clouds.DCC samples that are possibly contaminated by optically thinner clouds over the western Pacific may have caused the lower reflectivity there.However, even when we remove possible contaminated scenes (e.g., reflectivity lower than 0.95), the average of highly reflective clouds (i.e., Ref 0.6 > 0.95) is higher in the land regions: 0.99, 1.00, and 0.98 for Africa, South America, and western Pacific, respectively (Table 2).The persistent lower reflectivity strongly suggests that the contamination may not be the reason for the relatively low reflectivity over the west- SDs are about 1.2 µm for all three distributions, but average values are 24.8,22.4 µm, and 22. µm for the western Pacific, Africa, and South America, respectively, delineating relatively larger particles over the western Pacific.Because backward scattering tends to decrease while forward scattering slightly increases with respect to particle size, the difference in R e can also be considered as one of the reasons causing the regionally different DCC reflectivity over the tropical latitudes.Note that MODIS-derived cloud parameters such as COT and R e are based purely on visible and near-infrared radiance measurements (King et al., 1997).Thus, if measured radiances are smaller, especially for the 0.645 µm and 2.12 µm bands in the first place, smaller COT and/or larger R e of DCCs can arise from those measurements, as was also suggested by Doelling et al. (2013a).However, since MODIS-derived cloud properties cannot be independent of measured radiances themselves on focus, it should be difficult to examine measured characteristics from their derived properties.Because of this reasoning, we further use CloudSat and CALIPSO measurements to find possible causes.

CloudSat observations and derived cloud products
To avoid circular interpretation in the use of MODIS cloud products, we first use Cloud-Sat measurements to examine the regionally varying characteristics of tropical DCCs causing the different reflectivities.

Radar reflectivity profiles
The radar reflectivity profile is a fundamental observation of CloudSat that allows the examination of the vertical structure of DCC clouds.Two-dimensional histograms of the radar reflectivity for DCCs over Africa, South America, and the western Pacific and their corresponding mean profiles are given in Fig. 3.The two-dimensional distributions show similar parabolic shapes, but substantial differences exist between the western Pacific and the two continental regions, especially in the altitudes from 7 to 15 km Introduction

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Full (Fig. 3a-c).These features are more evident in the averaged profiles (Fig. 3d).Large radar echoes (e.g., greater than 10 dBZ) more frequently observed in the 7-15 km layer of DCCs over the continental regions, in comparison to the western Pacific counterpart.Moreover, maximum values of radar reflectivity for DCCs over the continental regions are located at relatively high altitudes (i.e., 9-10 km compared to 7-8 km).The larger reflectivity in the higher altitudes over the tropical continental areas implies stronger convective updraft there, as in large radar echoes introduced as a proxy of strong convection (Liu et al., 2007;Luo et al., 2008;Luo et al., 2011).These results are consistent with the finding that typical updrafts over the African Congo region are stronger than those over the tropical Pacific, and so lift larger particles into high altitudes (Liu and Zipser 2005;Zipser et al., 2006;Liu et al., 2007).CloudSat reflectivities of 0 or 10 dBZ are often used for tracing the precipitation-size particles within convective clouds (Stephens and Wood 2007).Here, to further examine DCC structure and related convection intensity, cloud top height is determined for each sample using the radar reflectivity threshold of −28 dBZ (Stephens et al., 2008).The highest altitudes showing radar reflectivities of −10, 0, and 10 dBZ (hereafter referred to as −10 dBZ height, 0 dBZ height, and 10 dBZ height) are also obtained.Average distributions are calculated from the obtained heights, −10, 0, and 10 dBZ heights, for the three analysis regions, and the results are given in Fig. 4. The mean distributions of cloud top heights for the DCCs show that the DCCs are in general slightly higher over the western Pacific compared to the African and South American regions (Fig. 4a).This result is consistent with the more frequent occurrence of cold clouds over the western Pacific (Fig. 2a).When the distributions of the highest altitudes showing −10, 0, and 10 dBZ reflectivities are compared, the difference appears to be more pronounced as the observed radar signal becomes larger.The distributions of −10 dBZ height seem to be similar among three regions (Fig. 4b).0 dBZ heights for the western Pacific appear to be generally lower than those of the other two regions, and a substantial portion exists even at levels below 12 km.The two land regions show a nearly identical distribution.In the case of the 10 dBZ height, a much broader distribution, with a peak Introduction

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Full located at the relatively low altitude of about 10 km, is apparent in the western Pacific DCCs compared to the land regions.Thus, radar reflectivity showing a relatively larger value (here 10 dBZ) appears at a comparatively lower level over the western Pacific region compared to Africa and South America.Overall, the upper part of DCCs over the western Pacific may be less dense because the 0 and 10 dBz heights are lower in spite of generally taller cloud compared to DCCs over tropical land regions.In other words, because the CloudSat radar reflectivity is proportional to the summed sixthpower of geometric particle size, the larger radar reflectivity in the upper part of clouds over the two land regions can be interpreted as either a larger amount of ice particles or larger sizes of ice there.

Profiles of ice water content (IWC)
As cloud particles have a direct effect on scattering and thus reflectivity, we examine the vertical distribution of IWC of DCCs collected over the three selected regions.Two-dimensional histograms of IWC and its mean vertical profiles are given in Fig. 5. Significant land-ocean contrast is evident in the IWC profiles; a much broader IWC range is shown over the two continental regions compared with the narrower IWC distribution over the western Pacific region.A majority of IWC over the western Pacific appears to have values smaller than 200 mg m −3 whereas there are much wider IWC distributions over two land regions up to 800-1000 mg m −3 , especially in layers below about 13 km.
The mean profiles of IWC of DCCs over the three regions summarize the tropical land-ocean contrast discussed above.IWC profiles appear to be similar in the upper part of the DCC layer (i.e., above 15 km).The differences in IWC between land and ocean and between the two land regions become substantial in layers below 15 km.The largest mean IWCs are shown over the South American region, and their magnitudes are as much as twice those for the western Pacific.The African region also shows a larger amount of IWC compared to that over the western Pacific, although values are smaller than those over the South American region.Overall, the zonal mean Introduction

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Full profile manifests that the total amount of ice water for DCCs over the western Pacific is much smaller than those in the two continental regions and that the level showing the maximum value is lower over the western Pacific.

Profiles of effective radius (R e ) for ice particles
Figure 6 represents CloudSat-derived R e profiles for DCCs over the three regions.It is noted that the narrower R e range with smaller particles in the upper part of DCC tends to become wider with larger particles in the lower layers.It is also of interest to note that maximum occurrence levels are significantly different between the land and ocean regions; maximum occurrences for the western Pacific are at about 15 km with particle sizes of 30-50 µm, but the two land regions show maximum occurrences at lower and thicker layers below 13 km with particle sizes larger than 100 µm.
The generally increasing tendency of R e with decreasing altitude is more evident in the averaged profiles (Fig. 6d).Even though a slight difference exists between the two land regions (i.e., African and South American domains) in the layer between 15 and 11 km, the two R e profiles are similar to each other, but these are clearly different from that of the western Pacific.In summary, R e for ice particles over the western Pacific is substantially smaller than those found for the two land regions, especially below the altitude of 15 km.These CloudSat results in effective radius appear to contradict the MODIS results in Fig. 2d, which show a much smaller radius range (e.g., hardly larger than 30 µm) and rather larger sizes over the western Pacific.Furthermore, the gradual increase in particle sizes from South America to Africa and the western Pacific appears to be opposite to the result found from the CloudSat retrievals.

Profiles of extinction coefficient (k ext )
k ext in the visible band enables us to interpret features of cloud reflectivity at the TOA because COT is proportional to reflectivity and can be obtained by vertically integrating k ext in the cloud layer.As in Eq. ( 1), k ext in each layer can be determined from IWC Introduction

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Full and R e , thus larger k ext implies larger IWC, smaller effective radius, or both.Thus, the DCC optical properties of a smaller amount of ice water and smaller particle sizes over the western Pacific region determined from CloudSat measurements seem to have a compensating effect on k ext .The resultant k ext profiles associated with ice water of DCCs are given in Fig. 7.The figure shows that the general patterns of the k ext profiles are very similar to the IWC profiles in Fig. 5, suggesting that the effect from different radius between land and ocean regions and between Africa and South America is minor.In other words, k ext is controlled largely by the amount of ice water content.
In the average profiles (Fig. 7d), k ext over the western Pacific is much smaller than those over Africa and South America, again similar to the IWC profiles.These results strongly suggest that among the three analysis domains reflectivity is lowest over the western Pacific, mainly because of the smaller amount of ice cloud particles there, compared to the tropical continental African and South American regions.

CALIPSO-derived ice water path (IWP) and COT
As CALIPSO uses a visible wavelength, it can observe optical properties related to small particles such as ice crystals, but observation is limited to small optical thickness because of the fast attenuation of emitted radiation.DCC heights determined from CALIPSO are relatively high, up to 2 km, compared to CloudSat-determined DCC heights, and CALIPSO observation is generally available for only a 1-3 km depth below the CALIPSO-determined cloud top in the case of convective clouds (not shown).
The cloud depth detectable from CALIPSO measurements tends to be slightly thicker over the western Pacific than over the central Africa and South America regions (not shown), suggesting that ice water density of the upper part of DCCs over the western Pacific is lower than that in the other two regions.
In order to investigate features of optical properties above the CloudSat more fluctuating pattern found for Africa that is probably an effect of the smaller sample size.The similarity of the PDFs found among the three analysis domains strongly suggests that the contribution from ice particles above the CloudSat-determined cloud top to the regionally different reflectivity is minor.Furthermore, magnitudes of IWP and COT seem too small when a majority of DCCs shows COT larger than 100 (Fig. 2).
Thus, the contribution of ice particles residing in the uppermost layers of DCCs, only detected by CALIPSO measurements, to the regional difference of reflectivity should be insignificant.

Conclusions and discussion
It has been reported that DCCs over the tropical western Pacific are generally darker (i.e., lower reflectivity) compared with the reflectivities of DCCs over tropical Africa and South America.In order to examine the main cause of the lower reflectivity over the western Pacific, we first examined the regional differences in cloud optical properties observed in satellite measurements of MODIS (Aqua), CloudSat, and CALIPSO.In doing so, DCC was defined as cloud whose cloud top temperature is colder than The collocated CloudSat observations revealed that heights showing large radar echoes (e.g., 10 dBZ) appear to be lower over the western Pacific.At the same time, both IWC and R e of ice particles in DCCs are smaller over the western Pacific.Furthermore, vertical distributions of k ext calculated from IWC and R e profiles are evidently smaller over the western Pacific, possibly leading to the lower COT and then lower TOA reflectivity there.However, considering that smaller particles contribute more to the backscattered radiation, the smaller particles over the western Pacific from Cloud-Sat measurements cannot explain the comparatively lower reflectivity.These results strongly suggest that darker DCCs over the western Pacific are mainly caused by the smaller amount of ice water content compared to those of the tropical Africa and South America regions.
The regional differences in DCC's optical properties noted in this study cast a cautionary warning for the ubiquitous use of DCCs for the solar channel calibration without taking those different factors into account.On the other hand, the results also suggest a way how DCC samples can be better selected over the western Pacific for the solar channel calibration.For instance, instead of using the same criteria to determine the DCCs everywhere over the globe (e.g.TB 11 = 205 K), regionally different criteria at least between the land and ocean can be introduced.It is because, as shown in Fig. 2 and Table 2,   Full

(
DCC) targets is interesting because DCCs are highly reflective and thus can serve as Discussion Paper | Discussion Paper | Discussion Paper | , CloudSat, and CALIPSO measurements MODIS is a passive imager having 36 spectral bands that cover the visible and infrared spectrum.In this study, brightness temperature at 11 µm (TB 11 ) and reflectivity at 0.645 µm (Ref 0.6 ) converted from MODIS-measured radiances (MYD021 products; Collection-5 version) are used to define DCC and to examine characteristic reflec-Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | America (10 • N-30 • S, 40-70 • W), and the oceanic western Pacific (20 • N-20 • S, 100-180 • E).Collocation data of Aqua MODIS, CloudSat, and CALIPSO measurements are constructed for the four January months in the 2007-2010 period.
Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ern Pacific.In other words, highly reflective clouds found over the western Pacific are generally darker compared to the two continental regions.PDF distributions of R e of the DCCs for the three regions are given in Fig. 2d.The overall shapes, showing a type of normal distribution, are similar to each other; but the Discussion Paper | Discussion Paper | Discussion Paper | R e modes are evidently different between the western Pacific and tropical land regions.
Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | -detected cloud top, IWP and COT are calculated by vertically integrating CALIPSO-derived layermean IWC and k ext profiles, respectively.PDF distributions for IWP and COT are given in Fig. 8.The figure shows that all the PDF distributions are nearly similar despite the Discussion Paper | Discussion Paper | Discussion Paper | 205 K (i.e., TB 11 < 205 K).From the MODIS-derived DCCs collected from the four January months of the 2007-2010 period, it was shown that the DCCs found over the western Pacific are colder and darker than the DCCs found over the Africa and South America domains(198.8K vs. 199.6 and 200.2 K, and 0.93 vs. 0.98 and 0.98).MODISderived COTs of DCCs showed that DCCs over the western Pacific determined by applying TB 11 = 205 K as a threshold are optically thinner than those over the two land regions.This may suggest that only the criterion of TB 11 = 205 K allowed more optically thinner convective/anvil-type clouds over the western Pacific region.However, considering the fact that the mean reflectivity of highly reflective clouds (i.e., Ref 0.6 > 0.95) was also higher in the land regions (i.e., 0.99, 1.00, and 0.98 for Africa, South America, and the western Pacific, respectively), DCCs over the western Pacific should generally be darker compared to those over the two tropical land regions.Discussion Paper | Discussion Paper | Discussion Paper | the use of more stringent criteria of TB 11 = 195 K over the western Pacific area may bring in DCCs, which are comparable, in terms of their occurrence and reflectivity, to those from the use of TB = 205 K over South America or Africa.Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | tivity features, respectively.MODIS-derived cloud parameters such as cloud optical thickness (COT) and column-integrated effective radius (R e ) are obtained from MYD06 products in order to analyze differences in cloud parameters between land and ocean regions in interest.All data are from MODIS Aqua products (http://ladsweb.nascom.nasa.gov/data/search.html).

A cautionary use of DCC as a solar calibration target Introduction
• E), South

Table 1 .
The numbers of MODIS-CloudSat collocated DCC pixels over the three analysis regions.