scholarly journals Investigating the frequency and trends in global above-cloud aerosol characteristics with CALIOP and OMI

2015 ◽  
Vol 15 (4) ◽  
pp. 4173-4217 ◽  
Author(s):  
R. Alfaro-Contreras ◽  
J. Zhang ◽  
J. R. Campbell ◽  
J. S. Reid
Keyword(s):  
Orthogonal Polarization ◽  
Ozone Monitoring Instrument ◽  
Regional Trends ◽  
Data Record ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Increasing Trends ◽  
First Time ◽  
Aerosol Index

Abstract. Seven and a half years (June 2006–November 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud layer products are compared with collocated Ozone Monitoring Instrument (OMI) Aerosol Index (AI) data and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products, to investigate variability in estimates of bi-annual and monthly above-cloud aerosol (ACA) events globally. The active- (CALIOP) and passive-based (OMI-MODIS) techniques have their advantages and caveats for ACA detection, and thus both are used to get a thorough and robust comparison of daytime cloudy-sky ACA distribution and climatology. For the first time, baseline above-cloud aerosol optical depth (ACAOD) and AI thresholds are derived and examined (AI = 1.0, ACAOD = 0.015) for each sensor. Both OMI-MODIS and CALIOP-based daytime spatial distributions of ACA events show similar patterns during both study periods (December–May) and (June–November). Divergence exists in some regions, however, such as Southeast Asia during June through November, where daytime cloudy-sky ACA frequencies of up to 10% are found from CALIOP yet are non-existent from the OMI-based method. Conversely, annual cloudy-sky ACA frequencies of 20–30% are reported over Northern Africa from the OMI-based method, yet are largely undetected by the CALIOP-based method. This is possibly due to a misclassification of thick dust plumes as clouds by the OMI-MODIS based method. An increasing trend of ~0.5% per year (since 2009) in global monthly cloudy-sky ACA daytime frequency of occurrence is found using the OMI-MODIS based method. Yet, CALIOP-based global daytime ACA frequencies exhibit a near-zero trend. Further analysis suggests that the OMI derived cloudy-sky ACA frequency trend may be affected by OMI row anomalies in later years. A few regions are found to have increasing trends of cloudy-sky ACA frequency, including the Middle-East and India. Regions with slightly negative cloudy-sky ACA frequency trends are found over South America and the Southern Oceans, while remaining regions in the study show a near-zero trend. Global and regional trends are not statistically significant, though, given relatively lacking sample sizes. A longer data record of ACA events is needed in order to establish a more significant trend of ACA frequency regionally and globally.

scholarly journals Investigating the frequency and interannual variability in global above-cloud aerosol characteristics with CALIOP and OMI

2016 ◽  
Vol 16 (1) ◽  
pp. 47-69 ◽  
Author(s):  
R. Alfaro-Contreras ◽  
J. Zhang ◽  
J. R. Campbell ◽  
J. S. Reid
Keyword(s):  
Interannual Variability ◽  
Orthogonal Polarization ◽  
Cloud Detection ◽  
Ozone Monitoring Instrument ◽  
Data Set ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
First Time ◽  
Aerosol Index

Abstract. Seven and a half years (June 2006 to November 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud layer products are compared with collocated Ozone Monitoring Instrument (OMI) aerosol index (AI) data and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products in order to investigate variability in estimates of biannual and monthly above-cloud aerosol (ACA) events globally. The active- (CALIOP) and passive-based (OMI-MODIS) techniques have their advantages and caveats for ACA detection, and thus both are used to derive a thorough and robust comparison of daytime cloudy-sky ACA distribution and climatology. For the first time, baseline above-cloud aerosol optical depth (ACAOD) and AI thresholds are derived and examined (AI  =  1.0, ACAOD  =  0.015) for each sensor. Both OMI-MODIS and CALIOP-based daytime spatial distributions of ACA events show similar patterns during both study periods (December–May) and (June–November). Divergence exists in some regions, however, such as Southeast Asia during June through November, where daytime cloudy-sky ACA frequencies of up to 10 % are found from CALIOP yet are non-existent from the OMI-based method. Conversely, annual cloudy-sky ACA frequencies of 20–30 % are reported over northern Africa from the OMI-based method yet are largely undetected by the CALIOP-based method. Using a collocated OMI-MODIS-CALIOP data set, our study suggests that the cloudy-sky ACA frequency differences between the OMI-MODIS- and CALIOP-based methods are mostly due to differences in cloud detection capability between MODIS and CALIOP as well as QA flags used. An increasing interannual variability of  ∼  0.3–0.4 % per year (since 2009) in global monthly cloudy-sky ACA daytime frequency of occurrence is found using the OMI-MODIS-based method. Yet, CALIOP-based global daytime ACA frequencies exhibit a near-zero interannual variability. Further analysis suggests that the OMI-derived interannual variability in cloudy-sky ACA frequency may be affected by OMI row anomalies in later years. A few regions are found to have increasing slopes in interannual variability in cloudy-sky ACA frequency, including the Middle East and India. Regions with slightly negative slopes of the interannual variability in cloudy-sky ACA frequencies are found over South America and China, while remaining regions in the study show nearly zero change in ACA frequencies over time. The interannual variability in ACA frequency is not, however, statistically significant on both global and regional scales, given the relatively limited sample sizes. A longer data record of ACA events is needed in order to establish significant trends of ACA frequency regionally and globally.

scholarly journals Estimates of aerosol absorption over India using multi-satellite retrieval

2013 ◽  
Vol 31 (10) ◽  
pp. 1773-1778 ◽  
Author(s):  
D. Narasimhan ◽  
S. K. Satheesh
Keyword(s):  
Regional Distribution ◽  
Single Scattering ◽  
Ozone Monitoring Instrument ◽  
Satellite Retrieval ◽  
Aerosol Absorption ◽  
Moderate Resolution ◽  
Indian Landmass ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
First Time

Abstract. Aerosol absorption is poorly quantified because of the lack of adequate measurements. It has been shown that the Ozone Monitoring Instrument (OMI) aboard EOS-Aura and the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard EOS-Aqua, which fly in formation as part of the A-train, provide an excellent opportunity to improve the accuracy of aerosol retrievals. Here, we follow a multi-satellite approach to estimate the regional distribution of aerosol absorption over continental India for the first time. Annually and regionally averaged aerosol single-scattering albedo over the Indian landmass is estimated as 0.94 ± 0.03. Our study demonstrates the potential of multi-satellite data analysis to improve the accuracy of retrieval of aerosol absorption over land.

scholarly journals Μελέτη επεισοδίων αερολυμάτων στην ευρύτερη περιοχή της λεκάνης της Μεσογείου με τη χρήση σύγχρονων δορυφορικών δεδομένων

2012 ◽  
Author(s):  
Αντώνιος Γκίκας
Keyword(s):  
North Atlantic ◽  
Fine Fraction ◽  
Total Ozone Mapping Spectrometer ◽  
Ozone Monitoring Instrument ◽  
Santa Barbara ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Atmospheric Radiative Transfer ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Aerosol Index

Στην παρούσα Διδακτορική Διατριβή, μελετάται το καθεστώς των επεισοδίων αερολυμάτων στην ευρύτερη περιοχή της λεκάνης της Μεσογείου, κατά την περίοδο 2000-2007. Πιο συγκεκριμένα, μελετώνται τα χωρικά και χρονικά χαρακτηριστικά της συχνότητας εμφάνισής τους, της έντασής τους και της διάρκειάς τους, ο ρόλος της ατμοσφαιρικής κυκλοφορίας που ευνοεί την εκδήλωσή τους, καθώς και η διαταραχή του ισοζυγίου της ηλιακής ακτινοβολίας που αυτά προκαλούν. Η ταυτοποίηση των επεισοδίων αερολυμάτων πραγματοποιείται με έναν αντικειμενικό και δυναμικό αλγόριθμο, ο οποίος αναπτύχθηκε στα πλαίσια της Διδακτορικής Διατριβής. Μέσω του αλγορίθμου, ορίζονται τα επίπεδα αποκοπής (threshold levels) και ταξινομούνται τα επεισόδια, με βάση την έντασή τους, σε ισχυρά και ακραία, καθώς και με βάση τον τύπο τους. Σε ό,τι αφορά στο δεύτερο διαχωρισμό, προέκυψαν οι εξής πέντε (5) τύποι επεισοδίων: (i) επεισόδια αερολυμάτων από αστικές/βιομηχανικές δραστηριότητες και καύση βιομάζας (Biomass Urban episodes, BU), (ii) επεισόδια αερολυμάτων ερημικής σκόνης (Desert Dust episodes, DD) (iii) επεισόδια αερολυμάτων θαλάσσιου τύπου (Sea-Salt-like episodes, SS-like), (iv) επεισόδια μίξης αερολυμάτων διαφορετικού τύπου (Mixed episodes, MX) και (v) επεισόδια τα οποία δεν κατατάσσονται σε κάποιον από τους προηγούμενους τύπους (Undetermined episodes, UN). Ως δεδομένα εισαγωγής στον αλγόριθμο χρησιμοποιούνται ημερήσιες δορυφορικές μετρήσεις, σε πλεγματική μορφή χωρικής ανάλυσης 1ox1o γεωγραφικού πλάτους και μήκους, για το οπτικό βάθος αερολυμάτων (Aerosol Optical Depth, AOD), τον εκθετικό παράγοντα Ångström (α) των αερολυμάτων, το δείκτη αερολυμάτων (Aerosol Index, ΑΙ), την αναλογία λεπτόκοκκων αερολυμάτων ως προς το σύνολό τους (Fine Fraction, FF) και τη μέση ενεργό ακτίνα (effective radius, reff). Τα δεδομένα αυτά ελήφθησαν από τους δορυφόρους MODIS (MODerate Resolution Imaging Spectroradiometer)-Terra, EP-TOMS (Earth Probe-Total Ozone Mapping Spectrometer) και ΟΜΙ (Ozone Monitoring Instrument)-Aura.Σε ετήσια βάση, τα ισχυρά επεισόδια εκδηλώνονται περισσότερο συχνά (έως 13.3 επεισόδια/έτος) στη Δ. Μεσόγειο και λιγότερο συχνά στην Α. Μεσόγειο (έως 2 επεισόδια/έτος). Αντίθετα, τα ακραία επεισόδια εκδηλώνονται με μεγαλύτερη συχνότητα στην Κ. Μεσόγειο (4 επεισόδια/έτος), ενώ οι μικρότερες συχνότητες παρατηρούνται στα βόρεια τμήματα της Βαλκανικής Χερσονήσου (0.3 επεισόδια/έτος). Η ένταση των ισχυρών επεισοδίων (εκπεφρασμένη σε τιμές AOD στα 550nm) κυμαίνεται μεταξύ 0.43 και 1.5, ενώ η ένταση των ακραίων επεισοδίων είναι μεγαλύτερη και κυμαίνεται μεταξύ 0.67 και 4.07. Κοινό χαρακτηριστικό, αποτελεί η μείωση της έντασης των επεισοδίων προς τα βορειότερα γεωγραφικά πλάτη, κυρίως εξαιτίας της εξασθένησης του μηχανισμού μεταφοράς ερημικής σκόνης. Το μεγαλύτερο ποσοστό (> 85%) των ισχυρών και ακραίων επεισοδίων διαρκεί μία (1) ημέρα. Κατά τη διάρκεια του έτους, τα επεισόδια εκδηλώνονται με μεγαλύτερη συχνότητα τους καλοκαιρινούς (Δ. Μεσόγειος) και εαρινούς μήνες (Κ. και Α. Μεσόγειος), ενώ το αντίστροφο ισχύει για το χειμώνα (επίδραση της βροχόπτωσης). Η συχνότητα εμφάνισης των επεισοδίων, κατά την περίοδο 2000-2007, εμφανίζει πτωτικές τάσεις (έως 100%), ενώ δεν παρατηρούνται σημαντικές τάσεις μεταβολής της έντασής τους.Το μεγαλύτερο ποσοστό των ισχυρών και κυρίως των ακραίων επεισοδίων στην περιοχή απαρτίζεται από επεισόδια ερημικής σκόνης (έως 71.5%), ενώ τα μικρότερα ποσοστά καταγράφονται για τα BU επεισόδια (έως 1.5%). Η περισσότερο συχνή εμφάνιση των επεισοδίων παρατηρείται: για τα BU επεισόδια (έως 1 επεισόδιο/έτος) στα βόρεια τμήματα της Βαλκανικής Χερσονήσου, για τα DD επεισόδια στη Δ. Μεσόγειο (έως 11.4 επεισόδια/έτος), για τα SS-like επεισόδια στην Ιβηρική Χερσόνησο και στη Χερσόνησο της Ανατολίας (3.9 επεισόδια/έτος) και για τα ΜΧ επεισόδια στα δυτικά τμήματα της θάλασσας της Μεσογείου (5 επεισόδια/έτος). Η μεγαλύτερη ένταση των ισχυρών BU επεισοδίων σημειώνεται στην Κοιλάδα του Πάδου (1.2) στην Ιταλία, ενώ για τα DD, SS-like και ΜΧ επεισόδια στον Κόλπο της Σίδρας και στη θαλάσσια περιοχή της Λιβύης (έως 1.6). Σε μεμονωμένες περιπτώσεις η ένταση των ακραίων SS-like και ΜΧ επεισοδίων μπορεί να ανέλθει έως 5 (τιμές AOD στα 550nm). Η μέγιστη συχνότητα, σε μηνιαία και περιοχική κλίμακα, των ισχυρών BU επεισοδίων σημειώθηκε τον Αύγουστο του 2003 (0.13 επεισόδια/κυψελίδα). Η ανάλυση μας αναδεικνύει χαρακτηριστικά εποχικού κύκλου για τα ισχυρά και ακραία DD επεισόδια, με τις μέγιστες συχνότητες να σημειώνονται τη ξηρή περίοδο του έτους και την άνοιξη, αντίστοιχα. Σύμφωνα με τα αποτελέσματά μας, προκύπτει συσχέτιση της συχνότητας εμφάνισης των DD επεισοδίων με την κύμανση του Βορείου Ατλαντικού (North Atlantic Oscillation, ΝΑΟ) που είναι σε συμφωνία με ευρήματα προηγούμενων μελετών που ανέφεραν συσχέτιση του φορτίου των ερημικών αερολυμάτων στη Μεσόγειο με το ΝΑΟ. Με την εφαρμογή του μοντέλου HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) μελετήθηκαν οι τροχιές των αερίων μαζών, για μια περίοδο 5 ημερών πριν την εκδήλωση ακραίων επεισοδίων διαφορετικών τύπων. Τέλος, τα αποτελέσματα του αλγορίθμου, για τις περιπτώσεις DD επεισοδίων, αξιολογήθηκαν επιτυχώς έναντι επίγειων μετρήσεων συγκέντρωσης του σωματιδιακού φορτίου (Dust PM10) και οπτικών ιδιοτήτων (AERONET).Επιχειρήθηκε, επίσης, η περιγραφή της ατμοσφαιρικής κυκλοφορίας, στην κατώτερη τροπόσφαιρα, και ο ρόλος της στην εκδήλωση επεισοδίων στην ευρύτερη περιοχή της λεκάνης της Μεσογείου. Για το σκοπό αυτό, τέθηκαν κριτήρια επιλογής των ημερών μελέτης, για τις οποίες η ατμοσφαιρική κυκλοφορία ταξινομήθηκε αντικειμενικά, με την εφαρμογή πολυμεταβλητών στατιστικών μεθόδων, όπως αυτών της Παραγοντικής Ανάλυσης (Factor Analysis S-mode) και της Ανάλυσης κατά Συστάδες (Cluster Analysis). Από την εφαρμοσθείσα μεθοδολογία, προέκυψαν 8 τύποι ατμοσφαιρικής κυκλοφορίας των οποίων τα χαρακτηριστικά περιγράφηκαν, ενώ προσδιορίστηκαν οι γεωγραφικές κατανομές της συχνότητας εμφάνισης των επεισοδίων, της έντασής τους και της επικράτησής τους (ισχυρά ή ακραία), για την κάθε Ομάδα (Cluster). Αντίστοιχη μελέτη πραγματοποιήθηκε και για την περιγραφή των τύπων ανάπτυξης της ατμοσφαιρικής κυκλοφορίας που οδηγούν στην πρόκληση επεισοδίων μεταφοράς ερημικής σκόνης, καταλήγοντας σε 6 Ομάδες. Τέλος, υπολογίστηκε η άμεση διαταραχή του ισοζυγίου της ακτινοβολίας (direct radiative effect, DRE) που προκαλείται από την εκδήλωση ακραίων επεισοδίων, διαφορετικού τύπου, υπό συνθήκες ανέφελου ουρανού. Οι υπολογισμοί πραγματοποιήθηκαν στην κορυφή της ατμόσφαιρας (TOA), στην ατμόσφαιρα (atmab) και στο έδαφος (surf, surfnet) με την εφαρμογή του μοντέλου διάδοσης ακτινοβολίας SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer). Σε τοπικό επίπεδο, κατά την εκδήλωση ακραίων DD επεισοδίων πάνω από θάλασσα, το σύστημα Γης-ατμόσφαιρας ψύχεται ανακλώντας περισσότερη ηλιακή ακτινοβολία κατά 85 W/m2, η ατμόσφαιρα θερμαίνεται απορροφώντας περισσότερη ηλιακή ακτινοβολία κατά 408 W/m2, ενώ το έδαφος ψύχεται δεχόμενο λιγότερη ακτινοβολία κατά 493 W/m2. Επίσης, ο υπολογιζόμενος ρυθμός θέρμανσης της ατμόσφαιρας, λόγω των επεισοδίων DD, ανέρχεται σε έως και 10 Κ/day, στα 2.5 Km, επιφέροντας σημαντικές τροποποιήσεις στη δυναμική της.

scholarly journals A Climatological Assessment of Intense Desert Dust Episodes over the Broader Mediterranean Basin Based on Satellite Data

2021 ◽  
Vol 13 (15) ◽  
pp. 2895
Author(s):  
Maria Gavrouzou ◽  
Nikolaos Hatzianastassiou ◽  
Antonis Gkikas ◽  
Christos J. Lolis ◽  
Nikolaos Mihalopoulos
Keyword(s):  
Mediterranean Basin ◽  
Eastern Mediterranean ◽  
Mean Value ◽  
Early Spring ◽  
Dust Aerosol ◽  
Ozone Monitoring Instrument ◽  
Central Mediterranean ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer

A satellite algorithm able to identify Dust Aerosols (DA) is applied for a climatological investigation of Dust Aerosol Episodes (DAEs) over the greater Mediterranean Basin (MB), one of the most climatologically sensitive regions of the globe. The algorithm first distinguishes DA among other aerosol types (such as Sea Salt and Biomass Burning) by applying threshold values on key aerosol optical properties describing their loading, size and absorptivity, namely Aerosol Optical Depth (AOD), Aerosol Index (AI) and Ångström Exponent (α). The algorithm operates on a daily and 1° × 1° geographical cell basis over the 15-year period 2005–2019. Daily gridded spectral AOD data are taken from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua Collection 6.1, and are used to calculate the α data, which are then introduced into the algorithm, while AI data are obtained by the Ozone Monitoring Instrument (OMI) -Aura- Near-UV aerosol product OMAERUV dataset. The algorithm determines the occurrence of Dust Aerosol Episode Days (DAEDs), whenever high loads of DA (higher than their climatological mean value plus two/four standard deviations for strong/extreme DAEDs) exist over extended areas (more than 30 pixels or 300,000 km2). The identified DAEDs are finally grouped into Dust Aerosol Episode Cases (DAECs), consisting of at least one DAED. According to the algorithm results, 166 (116 strong and 50 extreme) DAEDs occurred over the MB during the study period. DAEDs are observed mostly in spring (47%) and summer (38%), with strong DAEDs occurring primarily in spring and summer and extreme ones in spring. Decreasing, but not statistically significant, trends of the frequency, spatial extent and intensity of DAECs are revealed. Moreover, a total number of 98 DAECs was found, primarily in spring (46 DAECs) and secondarily in summer (36 DAECs). The seasonal distribution of the frequency of DAECs varies geographically, being highest in early spring over the eastern Mediterranean, in late spring over the central Mediterranean and in summer over the western MB.

scholarly journals A high spatial resolution retrieval of NO<sub>2</sub> column densities from OMI: method and evaluation

2011 ◽  
Vol 11 (4) ◽  
pp. 12411-12440 ◽  
Author(s):  
A. R. Russell ◽  
A. E. Perring ◽  
L. C. Valin ◽  
E. Bucsela ◽  
E. C. Browne ◽  
...  
Keyword(s):  
Boundary Layer ◽  
The Arctic ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Aircraft Observations ◽  
Vertical Column Density ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Better Than

Abstract. We present a new retrieval of tropospheric NO2 vertical column density from the Ozone Monitoring Instrument (OMI) based on high spatial and temporal resolution terrain and profile inputs. We find non-negligible impacts on the retrieved NO2 column for terrain pressure (±20%), albedo (±40%), and NO2 vertical profile (−75%–+10%). We compare our NO2 product, the Berkeley High-Resolution (BEHR) product, with operational retrievals and find that the operational retrievals are biased high (30%) over remote areas and biased low (8%) over urban regions. We validate the operational and BEHR products using boundary layer aircraft observations from the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS-CA) field campaign which occurred in June 2008 in California. Results indicate that columns derived using our boundary layer extrapolation method show good agreement with satellite observations (R2 = 0.65–0.83; N = 68) and provide a more robust validation of satellite-observed NO2 column than those determined using full vertical spirals (R2 = 0.26; N = 5) as in previous work. Agreement between aircraft observations and the BEHR product (R2 = 0.83) is better than agreement with the operational products (R2 = 0.65–0.72). We also show that agreement between satellite and aircraft observations for all products can be further improved (e.g. BEHR: R2 = 0.91) using cloud information from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument instead of the OMI cloud product. These results indicate that much of the variance in the operational products can be attributed to coarse resolution terrain and profile parameters.

scholarly journals MODIS Cloud Detection Evaluation Using CALIOP over Polluted Eastern China

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 333 ◽  
Author(s):  
Saichun Tan ◽  
Xiao Zhang ◽  
Guangyu Shi
Keyword(s):  
Eastern China ◽  
Cloud Fraction ◽  
Orthogonal Polarization ◽  
Aerosol Layer ◽  
Cloud Detection ◽  
Haze Pollution ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Cloud Optical Thickness ◽  
Moderate Resolution Imaging Spectroradiometer

Haze pollution has frequently occurred in winter over Eastern China in recent years. Over Eastern China, Moderate Resolution Imaging Spectroradiometer (MODIS) cloud detection data were compared with the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) for three years (2013–2016) for three kinds of underlying surface types (dark, bright, and water). We found that MODIS and CALIOP agree most of the time (82% on average), but discrepancies occurred at low CALIOP cloud optical thickness (COT < 0.4) and low MODIS cloud top height (CTH < 1.5 km). In spring and summer, the CALIOP cloud fraction was higher by more than 0.1 than MODIS due to MODIS’s incapability of observing clouds with a lower COT. The discrepancy increased significantly with a decrease in MODIS CTH and an increase in aerosol optical depth (AOD, about 2–4 times), and MODIS observed more clouds that were undetected by CALIOP over PM2.5 > 75 μg m−3 regions in autumn and particularly in winter, suggesting that polluted weather over Eastern China may contaminate MODIS cloud detections because MODIS will misclassify a heavy aerosol layer as cloudy under intense haze conditions. Besides aerosols, the high solar zenith angle (SZA) in winter also affects MODIS cloud detection, and the ratio of MODIS cloud pixel numbers to CALIOP cloud-free pixel numbers at a high SZA increased a great deal (about 4–21 times) relative to that at low SZA for the three surfaces. As a result of the effects of aerosol and SZA, MODIS cloud fraction was 0.08 higher than CALIOP, and MODIS CTH was more than 2 km lower than CALIOP CTH in winter. As for the cloud phases and types, the results showed that most of the discrepancies could be attributed to water clouds and low clouds (cumulus and stratocumulus), which is consistent with most of the discrepancies at low MODIS CTH.

scholarly journals A high spatial resolution retrieval of NO<sub> 2</sub> column densities from OMI: method and evaluation

2011 ◽  
Vol 11 (16) ◽  
pp. 8543-8554 ◽  
Author(s):  
A. R. Russell ◽  
A. E. Perring ◽  
L. C. Valin ◽  
E. J. Bucsela ◽  
E. C. Browne ◽  
...  
Keyword(s):  
Boundary Layer ◽  
The Arctic ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Aircraft Observations ◽  
Vertical Column Density ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Better Than

Abstract. We present a new retrieval of tropospheric NO2 vertical column density from the Ozone Monitoring Instrument (OMI) based on high spatial and temporal resolution terrain and profile inputs. We compare our NO2 product, the Berkeley High-Resolution (BEHR) product, with operational retrievals and find that the operational retrievals are biased high (30 %) over remote areas and biased low (8 %) over urban regions. Additionally, we find non-negligible impacts on the retrieved NO2 column for terrain pressure (±20 %), albedo (±40 %), and NO2 vertical profile (−75 %–+10 %). We validate the operational and BEHR products using boundary layer aircraft observations from the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS-CA) field campaign which occurred in June 2008 in California. Results indicate that columns derived using our boundary layer extrapolation method show good agreement with satellite observations (R2 = 0.65–0.83; N = 68) and provide a more robust validation of satellite-observed NO2 column than those determined using full vertical spirals (R2 = 0.26; N = 5) as in previous work. Agreement between aircraft observations and the BEHR product (R2 = 0.83) is better than agreement with the operational products (R2 = 0.65–0.72). We also show that agreement between satellite and aircraft observations can be further improved (e.g. BEHR: R2 = 0.91) using cloud information from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument instead of the OMI cloud product. These results indicate that much of the variance in the operational products can be attributed to coarse resolution terrain pressure, albedo, and profile parameters implemented in the retrievals.

scholarly journals The Continuity MODIS-VIIRS Cloud Mask

2020 ◽  
Vol 12 (20) ◽  
pp. 3334 ◽  
Author(s):  
Richard A. Frey ◽  
Steven A. Ackerman ◽  
Robert E. Holz ◽  
Steven Dutcher ◽  
Zach Griffith
Keyword(s):  
Infrared Imaging ◽  
Cloud Fraction ◽  
The Arctic ◽  
Orthogonal Polarization ◽  
Cloud Detection ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Hit Rates ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Cloud Mask

This paper introduces the Continuity Moderate Resolution Imaging Spectroradiometer (MODIS)-Visible Infrared Imaging Radiometer Suite (VIIRS) Cloud Mask (MVCM), a cloud detection algorithm designed to facilitate continuity in cloud detection between the MODIS (Moderate Resolution Imaging Spectroradiometer) on the Aqua and Terra platforms and the series of VIIRS (Visible Infrared Imaging Radiometer Suite) instruments, beginning with the Soumi National Polar-orbiting Partnership (SNPP) spacecraft. It is based on the MODIS cloud mask that has been operating since 2000 with the launch of the Terra spacecraft (MOD35) and continuing in 2002 with Aqua (MYD35). The MVCM makes use of fourteen spectral bands that are common to both MODIS and VIIRS so as to create consistent cloud detection between the two instruments and across the years 2000–2020 and beyond. Through comparison data sets, including collocated Aqua MODIS and Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) from the A-Train, this study was designed to assign statistical consistency benchmarks between the MYD35 and MVCM cloud masks. It is shown that the MVCM produces consistent cloud detection results between Aqua MODIS, SNPP VIIRS, and NOAA-20 VIIRS and that the quality is comparable to the standard Aqua MODIS cloud mask. Globally, comparisons with collocated CALIOP lidar show combined clear and cloudy sky hit rates of 88.2%, 87.5%, 86.8%, and 86.8% for MYD35, MVCM Aqua MODIS, MVCM SNPP VIIRS, and MVCM NOAA-20 VIIRS, respectively, for June through until August, 2018. For the same months and in the same order for 60S–60N, hit rates are 90.7%, 90.5%, 90.1%, and 90.3%. From the time series constructed from gridded daily means of 60S–60N cloud fractions, we found that the mean day-to-day cloud fraction differences/standard deviations in percent to be 0.68/0.55, 0.94/0.64, −0.20/0.50, and 0.44/0.82 for MVCM Aqua MODIS-MVCM SNPP VIIRS day and night, and MVCM NOAA-20 VIIRS-MVCM SNPP VIIRS day and night, respectively. It is seen that the MODIS and VIIRS 1.38 µm cirrus detection bands perform similarly but with MODIS detecting slightly more clouds in the middle to high levels of the troposphere and the VIIRS detecting more in the upper troposphere above 16 km. In the Arctic, MVCM Aqua MODIS and SNPP VIIRS reported cloud fraction differences of 0–3% during the mid-summer season and −3–4% during the mid-winter.

scholarly journals Satellite Observations of Cloud-Related Variations in Aerosol Properties

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 430 ◽  
Author(s):  
Tamás Várnai ◽  
Alexander Marshak
Keyword(s):  
Particle Size ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Cloud Amount ◽  
Orthogonal Polarization ◽  
Radiative Processes ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Aerosol Properties

This paper presents an overview of our efforts to characterize and better understand cloud-related changes in aerosol properties. These efforts primarily involved the statistical analysis of global or regional datasets of Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud observations. The results show that in oceanic regions, more than half of all aerosol measurements by passive satellite instruments come from near-cloud areas, where clouds and cloud-related processes may significantly modify aerosol optical depth and particle size. Aerosol optical depth is also shown to increase systematically with regional cloud amount throughout the Earth. In contrast, it is shown that effective particle size can either increase or decrease with increasing cloud cover. In bimodal aerosol populations, the sign of changes depends on whether coarse mode or small mode aerosols are most affected by clouds. The results also indicate that over large parts of Earth, undetected cloud particles are not the dominant reason for the satellite-observed changes with cloud amount, and that 3D radiative processes contribute about 30% of the observed near-cloud changes. The findings underline the need for improving our ability to accurately measure aerosols near clouds.

scholarly journals Calibration of global MODIS cloud amount using CALIOP cloud profiles

2020 ◽  
Author(s):  
Andrzej Z. Kotarba
Keyword(s):  
Cloud Amount ◽  
Satellite Observation ◽  
Cloud Fraction ◽  
Orthogonal Polarization ◽  
Polar Regions ◽  
Cloud Detection ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Cloud Mask

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) cloud detection procedure classifies instantaneous fields of view (IFOV) as either confident cloudy, probably cloudy, probably clear, or confident clear. The cloud amount calculation requires quantitative cloud fractions to be assigned to these classes. The operational procedure used by NASA assumes that confident clear and probably clear IFOV are cloud-free (cloud fraction 0 %), while the remaining categories are completely filled with clouds (cloud fraction 100 %). This study demonstrates that this best guess approach is unreliable, especially on a regional/ local scale. We use data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument flown on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission, collocated with MODIS/ Aqua IFOV. Based on 33,793,648 paired observations acquired in January and July 2015, we conclude that actual cloud fractions to be associated with MODIS cloud mask categories are 21.5 %, 27.7 %, 66.6 %, and 94.7 %. Spatial variability is significant, even within a single MODIS algorithm path, and the operational approach introduces uncertainties of up to 30 % of cloud amount, notably in the polar regions at night, and in selected locations over the northern hemisphere. Applications of MODIS data at ~10 degrees resolution (or finer) should first assess the extent of the error. Uncertainties were related to the efficiency of the cloud masking algorithm. Until the algorithm can be significantly modified, our method is a robust way to calibrate (correct) MODIS estimates. It can be also used for MODIS/ Terra data, and other missions where the footprint is collocated with CALIPSO.

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