| 1. |
- Achtert, Peggy, 1982-
(författare)
-
Lidar Measurements of Polar Stratospheric Clouds in the Arctic
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polar Stratospheric Clouds (PSCs) play a key role for ozone depletion in the polar stratosphere. Its magnitude depends on the type of PSC and its lifetime and extent. This thesis presents PSC observations conducted with the Esrange lidar and the space-borne CALIPSO lidar.PSCs are separated into three types according to their optical properties. The occurrence rate of the different types which are often observed simultaneously as well as their interaction and connection is not well understood. To better understand the processes that govern PSC formation, observations need to be combined with a detailed view of the atmospheric background in which PSCs develop, exist, and are transformed from one type to another.This thesis introduces a new channel of the Esrange lidar for temperature profiling at heights below 35 km. The design of this channel and first temperature measurements within PSCs and cirrus clouds are presented. This is an important step since the majority of PSC-related literature extracts temperatures within PSCs from reanalysis data.In contrast to ground–based measurements space–borne lidar does not rely on cloud–free conditions. Hence, it provides an unprecedented opportunity for studying the connection between PSCs and the underlying synoptic–scale conditions which manifest as tropospheric clouds. This thesis shows that most of the PSCs observed in the Arctic during winter 2007/08 occurred in connection with tropospheric clouds.A combined analysis of ground-based and space-borne lidar observation of PSCs in combination with microphysical modeling can improve our understanding of PSC formation. A first case study of this approach shows how a PSC that was formed by synoptic-scale processes is transformed into another type while passing the Scandinavian mountains.Today a variety of classification schemes provides inconsistent information on PSC properties and types. This thesis suggests a unified classification scheme for lidar measurements of PSCs.
|
|
| 2. |
- Achtert, Peggy, 1982-, et al.
(författare)
-
Pure rotational-Raman channels of the Esrange lidar for temperature and particle extinction measurements in the troposphere and lower stratosphere
- 2013
-
Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 6:1, s. 91-98
-
Tidskriftsartikel (refereegranskat)abstract
- The Department of Meteorology at Stockholm University operates the Esrange Rayleigh/Raman lidar at Esrange(68° N, 21° E) near the Swedish city of Kiruna. This paper describes the design and first measurements of the newpure rotational-Raman channel of the Esrange lidar. The Esrange lidar uses a pulsed Nd:YAG solid-state laser operating at 532 nm as light source with a repetition rate of 20 Hz and a pulse energy of 350 mJ. The minimum vertical resolution is 150m and the integration time for one profile is 5000 shots. The newly implemented channel allows for measurements of atmospheric temperature at altitudes below 35 km and is currently optimized for temperature measurements between 180 and 200 K. This corresponds to conditions in the lower Arctic stratosphere during winter. In addition to the temperature measurements, the aerosol extinction coefficientand the aerosol backscatter coefficient at 532 nm can be measured in dependently. Our filter-based design minimizes the systematic error in the obtained temperature profile to less than 0.51 K. By combining rotational-Raman measurements (5–35 km height) and the integration technique (30–80 kmheight), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the upper troposphere up to the mesosphere. With the improved setup, the system can be used to validate current lidar-based polar stratospheric cloud classification schemes. The new capability of the instrument measuring temperature and aerosol extinction furthermore enables studies of the thermal structure and variability of the upper troposphere/lower stratosphere. Although several lidars are operated at polar latitudes, there are few instruments that are capable of measuring temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratospherewith daylight capability.
|
|
