Continuous observations of synoptic-scale dust transport at the Nepal Climate Observatory-Pyramid (5079 m a.s.l.) in the Himalayas
R. Duchi1,7, P. Cristofanelli1, A. Marinoni1, P. Laj2, S. Marcq2, P. Villani2, K. Sellegri3, F. Angelini4, F. Calzolari1, G. P. Gobbi4, G. P. Verza5, E. Vuillermoz5, A. Sapkota6, and P. Bonasoni1,51CNR-Institute of Atmospheric Sciences and Climate, Bologna, Italy 2Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Grenoble 1-CNRS, Grenoble, France 3Laboratoire de Météorologie Physique, CNRS – Université Blaise Pascal, Aubière, France 4CNR-Institute of Atmospheric Sciences and Climate, Rome, Italy 5Ev-K2-CNR Committee, Bergamo, Italy 6Department of Environment Science and Engineering, Kathmandu University, Dhulikhel, Nepal 7Science and Technology Faculty, Urbino University, Urbino, Italy
Received: 20 Dec 2010 – Accepted for review: 24 Jan 2011 – Discussion started: 04 Feb 2011
Abstract. This study presents two years of continuous observations of physical aerosol properties at the GAW-WMO global station "Nepal Climate Observatory – Pyramid" (NCO-P, 27°57' N, 86°48' E), sited at 5079 m a.s.l. in the high Himalayan Khumbu Valley (Nepal). Measurements of aerosol number size distribution, aerosol optical depth (AOD) and single scattering albedo (SSA) are analysed from March 2006 to February 2008. By studying the temporal variations of coarse (1 μm < Dp ≤ 10 μm) particle number concentration, 53 mineral Dust Transport Events (DTEs) are identified, accounting for 22.2% of the analysed data-set. Such events occurred prevalently during pre-monsoon (for 30.6% of the period) and winter (22.1%) seasons. However, uncommon cases of mineral dust transport are observed even during the monsoon season. The main sources of mineral dust reaching NCO-P are identified in the arid regions not far from the measurement site, i.e. from Tibetan Plateau, and Lot-Thar deserts, which account for 52% of the dust transport days. Moreover, a non-negligible contribution can be attributed to the Arabian Peninsula (17%) and the Indo-Gangetic Plains (16%), as indicated by three dimensional (3-D) back-trajectory analyses performed with LAGRANTO model.
The observed DTEs lead to significant enhancements in the coarse aerosol number concentration (+513%) and coarse aerosol mass (+655%), as compared with average values observed in "dust-free" conditions ( 0.05 ± 0.11 cm−3 and 3.4 ± 3.7 μg m−3, respectively). During DTEs, SSA is higher (0.84–0.89) than on "dust-free" days (0.75–0.83), confirming the importance of this class of events as a driver of the radiative features of the regional Himalayan climate. Considering the dust events, a significant seasonal AOD increase (+37.5%) is observed in the post-monsoon, whereas lower increase (less than +11.1%) characterises the pre-monsoon and winter seasons confirming the influence of synoptic-scale mineral dust transports on the aerosol optical properties observed at NCO-P.
Duchi, R., Cristofanelli, P., Marinoni, A., Laj, P., Marcq, S., Villani, P., Sellegri, K., Angelini, F., Calzolari, F., Gobbi, G. P., Verza, G. P., Vuillermoz, E., Sapkota, A., and Bonasoni, P.: Continuous observations of synoptic-scale dust transport at the Nepal Climate Observatory-Pyramid (5079 m a.s.l.) in the Himalayas, Atmos. Chem. Phys. Discuss., 11, 4229-4261, doi:10.5194/acpd-11-4229-2011, 2011.