Seasonal migration of cirrus clouds by using CALIOP observations
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ORIGINAL PAPER
Seasonal migration of cirrus clouds by using CALIOP observations Jan‑Bai Nee1 · Chien‑Yin Lu1 Received: 18 June 2020 / Accepted: 22 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Cirrus clouds at heights of 10–18 km are investigated for the seasonal migrations based on 3 years observations of CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) in 2008–2012. Past studies have shown cirrus clouds migrate from their winter peaks in the equatorial regions to the maximum latitudes of ± 30° in the boreal summer as the migration of ITCZ (Intertropical Convergence Zone). However, this general picture does not show detailed distributions by including height, seasons and latitudinal dependences considering cirrus extended height and latitudinal coverages. We are also interested in understanding the occurrences of thin cirrus in the tropical tropopause and formation of all cirrus in the extratropics where little studies about their migration have been made. It is not well know if the summer enhancement in the extratropics is only related to the migration or by other factors. Cirrus distributions are studied in two height groups of low ( 15 km), and in three regions of EQ (− 15° to 15° latitudes), NH (15°–30°), and SH (− 15° to − 30°) for different seasons. Our results show a major part of cirrus, the low cirrus, migrate to the extratropics in the summer. Like ITCZ, they stay mostly in the north (64%) less in the south (36%) following the same migration pattern. High cirrus cloud is decoupled from ITCZ with the major part showing a boreal winter peak spread to higher latitudes with seasons. In the extratropics, enhanced production of high cirrus can be attributed to the convective production in the summer monsoons. The summer convective production is used to estimate the formation of equatorial high cirrus in terms of rapid convection or slow ascending with a ratio determined.
1 Introduction Cirrus clouds are composed of small and irregular shaped ice crystals which play important roles in affecting the climate and radiative transfer of the earth’s atmosphere (Liou 1986). Satellite measurements have shown cirrus clouds have the highest occurrence frequency of about 60% in the ITCZ with peak occurrence in the boreal winter (Wang et al. 1996; Dessler et al. 2006; Sassen et al. 2008, 2009; Nazaryan et al. 2008; Massie et al. 2010, 2013; Pandit et al. 2015). However, cirrus clouds do not always stay in the tropics but migrate with the season to higher latitudes as part of ITCZ activities (Sassen et al. 2008; Nazaryan et al. 2008). In the extratropics, cirrus occurrence in July was found to be a factor of three more than that in January by ground lidar
Responsible Editor: Sang-Woo Kim. * Jan‑Bai Nee [email protected] 1
observations (Das et al. 2009). This extratropical summer high may be related to the migration of cirrus clouds or by other factors. ITCZ is a region of intense connectivity by constituting the Hadley cell whose uprising branch can bring moisture t
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