Ground-based remote sensing of aerosol properties using the emission FTS in Ny-Ålesund, Spitsbergen (78°N)
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Ground-based remote sensing of aerosol properties using the emission FTS in Ny-Ålesund, Spitsbergen (78°N)_Ph_D__thesis_Denghui_Ji.pdf | 7.64 MB | Adobe PDF | View/Open |
Authors: | Ji, Denghui |
Supervisor: | Notholt, Justus |
1. Expert: | Notholt, Justus |
Experts: | Bösch, Hartmut |
Abstract: | Arctic amplification, the rapid warming of the Arctic compared to the global average, re mains partially understood. Key processes include temperature feedback, surface albedo feedback, and cloud and water vapor feedback, with aerosols playing a critical role. Since 2019, a Fourier-Transform Infrared Spectrometer (FTS) at the AWIPEV research base in Ny-Ålesund, Spitsbergen, has been used to mea... Arctic amplification, the rapid warming of the Arctic compared to the global average, re mains partially understood. Key processes include temperature feedback, surface albedo feedback, and cloud and water vapor feedback, with aerosols playing a critical role. Since 2019, a Fourier-Transform Infrared Spectrometer (FTS) at the AWIPEV research base in Ny-Ålesund, Spitsbergen, has been used to measure aerosol components. An algorithm based on the Line-by-Line Radiative Transfer Model and DIScrete Ordinate Radiative Transfer model (LBLDIS) was developed for retrieving aerosol composition. In order to show this measurement technique in details, a case study for an aerosol-only case is presented with data from the 10th of June 2020. In the aerosol-only case, the retrieval results show that sulfate (τ900cm−1=0.007 ± 0.0027) is the dominant aerosol during the whole day, followedbydust(τ900cm−1=0.0039 ± 0.0029) and black carbon (τ900cm−1=0.0017 ± 0.0007). Sea salt (τ900cm−1=0.0012 ± 0.0002), which has the weakest emission ability in the infrared waveband, shows the lowest AOD value. Such proportions of sulfate, dust and BC also show good agreement with MERRA-2 reanalysis data. Additionally, the comparison with a sun-photometer (AERONET) shows the daily variation of aerosol AOD retrieved from FTS to be similar with that of the sun-photometer. Based on this retrieval method, long time period observations dataset using FTS is retrieved and presented in this study. Based on the observed data, the infrared radiation effects of different aerosol compo sition are analyzed. The results show that the hygroscopic aerosols, such as sea salt and sulfate, have a warming effect in the Arctic during winter. These aerosols absorb atmospheric water vapor, leading to wet growth, increased size, and enhanced longwave downward radiation emission, defined as the Aerosol Infrared Radiation Effect (ARE). Observations of aerosols, especially their composition, are challenging during the Arctic winter. We use an emission Fourier Transform Spectrometer to measure aerosol composition. Observations show that the ARE of dry aerosols is limited to about 1.45 ±2.00 Wm−2. Wet growth significantly increases the ARE of aerosols. During winter, at relative humidity levels between 60% and 80%, wet aerosols exhibit the ARE approximately 10 times greater than dry aerosols. When relative humidity exceeds 80%, the effect can be up to 50 times higher (30- 100 Wm−2). Sea salt aerosols in Ny-Ålesund demonstrate high effect values, while non-hygroscopic aerosols like black carbon and dust show consistently low values. Reanalysis data indicates increased water vapor and sea salt aerosol optical depth in Ny-Ålesund after 2000, correlating with significant positive temperature anomalies in this area. Besides, wet aerosols can remain activated even in dry environments, continuously contributing high effects, thereby expanding the area affected by aerosol-induced warming. This warming effect may exacerbate Arctic warming, acting as a positive feedback mechanism. Additionally, the rapid Arctic warming, which is occurring faster than in other regions, leads to a meandering atmospheric circulation pattern. Recently, a new pathway for African dust transport to the Arctic has been identified. This study provides a detailed description of the Rapid Pathway (RP) and investigates the temporal variation of African dust influx into the Arctic via this route. Using GEOS-Chem model simulations, we demonstrate the RP’s enhanced efficiency in accelerating African dust transport to the Arctic within approximately one week, compared to other pathways. Our analysis reveals a significant shift in African dust transport routes after 2000, with a marked increase in dust transport through the central North Atlantic (RP region), particularly in March and April. ERA5 wind field data reveal significant positive anomalies in poleward winds over the North Atlantic in March and April after 2000, facilitating northward dust transport via the RP region. In contrast, negative wind anomalies over Europe suggest a diminished role for the European pathway in Arctic dust transport. |
Keywords: | aerosol; Arctic amplification; Fourier-Transform Infrared Spectrometer |
Issue Date: | 4-Dec-2024 |
Type: | Dissertation |
DOI: | 10.26092/elib/3517 |
URN: | urn:nbn:de:gbv:46-elib84913 |
Institution: | Universität Bremen |
Faculty: | Fachbereich 01: Physik/Elektrotechnik (FB 01) |
Appears in Collections: | Dissertationen |
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