Aerosol-cloud interactions are the most uncertain component of the anthropogenic radiative forcing. A substantial part of this uncertainty comes from the limitations of currently used spaceborne CCN proxies that (i) are column integrated and do not guarantee vertical co-location of aerosols and clouds, (ii) have retrieval issues over land, and (iii) do not account for aerosol hygroscopicity. A possible solution to overcome these limitations is to use height-resolved measurements of the spaceborne lidar aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. This thesis presents a novel CCN retrieval algorithm based on Optical Modelling of CALIPSO Aerosol Microphysics (OMCAM) that is designed particularly for CALIPSO lidar measurements, along with its validation with airborne and surface in-situ measurements.
\noindent OMCAM uses a set of normalized size distributions from the CALIPSO aerosol model and modifies them to reproduce the CALIPSO measured aerosol extinction coefficient. It then uses the modified size distribution and aerosol type-specific CCN parameterizations to estimate the number concentration of CCN (nCCN) at different supersaturations. The algorithm accounts for aerosol hygroscopicity by using the kappa parametrization. Sensitivity studies suggest that the uncertainty associated with the output nCCN may range between a factor of 2 and 3. OMCAM-estimated aerosol number concentrations (ANCs) and nCCN are validated using temporally and spatially co-located in-situ measurements. In the first part of validation, the airborne observations collected during the Atmospheric Tomography (ATom) mission are used. It is found that the OMCAM estimates of ANCs are in good agreement with the in-situ measurements with a correlation coefficient of 0.82, an RMSE of 247.2 cm-3, and a bias of 44.4 cm-3. The agreement holds for all aerosol types, except for marine aerosols, in which the OMCAM estimates are about an order of magnitude smaller than the in-situ measurements. An update of the marine model in OMCAM improve the agreement significantly. In the second part of validation, the OMCAM-estimated ANC and nCCN are compared to measurements from seven surface in-situ stations covering a variety of aerosol environments. The OMCAM-estimated monthly nCCN are found to be in reasonable agreement with the in-situ measurements with a 39 % normalized mean bias and 71 % normalized mean error. Combining the validation studies, the algorithm outputs are found to be consistent with the co-located in-situ measurements at different altitude ranges over both land and ocean. Such an agreement has not yet been achieved for spaceborne-derived CCN concentrations and demonstrates the potential of using CALIPSO lidar measurements for inferring global 3D climatologies of CCN concentrations related to different aerosol types.:1 Introduction . . . . . . . . . . . . . . . 1
1.1 Background: Aerosols in the climate system . . . . . . . . . . . . . . . . . 1
1.1.1 Aerosol-induced effective radiative forcing . . . . . . . . . . . . . . 3
1.1.2 Significance of aerosol-cloud interactions . . . . . . . . . . . . . . . 3
1.2 Observation-based ACI studies . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 In-situ studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.2 Spaceborne studies . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Spaceborne CCN proxies and their limitations . . . . . . . . . . . . . . . . 8
1.4 CCN concentrations from lidars . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5 Objective: CCN from spaceborne lidar . . . . . . . . . . . . . . . . . . . . 11
2 Paper 1: Estimating cloud condensation nuclei concentrations from
CALIPSO lidar measurements . . . . . . . . . . . . . . . 15
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 Data and retrievals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1 CALIPSO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 MOPSMAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2.3 POLIPHON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3.1 Aerosol size distribution . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3.2 Aerosol hygroscopicity . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.3 CCN parameterizations . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.4 Application of OMCAM to CALIPSO retrieval . . . . . . . . . . . 23
2.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.1 Sensitivity analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.2 Comparison with POLIPHON . . . . . . . . . . . . . . . . . . . . . 30
2.4.3 Case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.5 Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3 Paper 2: Evaluation of aerosol number concentrations from CALIPSO
with ATom airborne in situ measurements . . . . . . . . . . . . . . . 39
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.2 Data, retrievals, and methods . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2.1 ATom
3.2.2 CALIOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2.3 Aerosol number concentration from CALIOP . . . . . . . . . . . . 44
3.2.4 Data matching and comparison . . . . . . . . . . . . . . . . . . . . 48
3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.3.1 Example cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.3.2 General findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.6 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4 Paper 3: Assessment of CALIOP-derived CCN concentrations by in
situ surface measurements . . . . . . . . . . . . . . . 65
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.2 Data and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2.1 In situ observations . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.2.2 CALIOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.2.3 Comparison Methodology . . . . . . . . . . . . . . . . . . . . . . . 71
4.3 Comparison of CCN Concentrations . . . . . . . . . . . . . . . . . . . . . . 73
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5 Summary and conclusions . . . . . . . . . . . . . . . 79
6 Outlook . . . . . . . . . . . . . . . 83
References . . . . . . . . . . . . . . . 88
List of Abbreviations . . . . . . . . . . . . . . . 107
List of Variables . . . . . . . . . . . . . . . 109
List of Figures . . . . . . . . . . . . . . . 111
List of Tables . . . . . . . . . . . . . . . 113
A List of Publications . . . . . . . . . . . . . . . 115
B Acknowledgements . . . . . . . . . . . . . . . 117
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:83140 |
| Date | 30 January 2023 |
| Creators | Choudhury, Goutam |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/acceptedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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