Journal of Atmospheric and Solar-Terrestrial Physics 66 (2004) 393–405 www.elsevier.com/locate/jastp Eects of energetic solar proton events on the cyclone development in the North Atlantic S. Veretenenko a ; ∗ , P. Thejll b a InstituteofRadiophysics,UniversityofSt.Petersburg,St.Petersburg,Petrodvorets198904,Russia b DanishMeteorologicalInstitute,Lyngbyvej1000,CopenhagenDK-2100,Denmark Received 8 April 2003; received in revised form 3 November 2003; accepted 20 November 2003 Abstract Short-term eects of the energetic solar proton events (SPE) on the dierent characteristics of the lower atmosphere were studied in the North Atlantic region, which is an area of intensive cyclone genesis and development. The data of aerological soundings over the set of Danish stations (Greenland, Faeroe Islands and Denmark), the vorticity data at the dierent pressure levels and weather charts at the Earth’s surface were used. It was shown that the SPE under study are accompanied by noticeable pressure and temperature decreases at the high-latitudinal stations in the cold (October–March) half of year as well as by relative vorticity increases in the troposphere. The most pronounced eects were found in the region of the arctic front near the south-eastern Greenland coasts and Iceland. The weather chart analysis showed that the eects discovered seem to be related to the intensication of the deepening of well developed cold cyclones in this region. The results obtained suggest that the SPE with particle energies sucient to penetrate the stratospheric heights may inuence the cyclone evolution over the northern part of the Atlantic Ocean, a possible physical mechanism involving the radiative forcing of the cloudiness changes which may be associated with cosmic ray variations. c 2004 Elsevier Ltd. All rights reserved. Keywords: Solar activity; Cosmic rays; Weather; Climate 1. Introduction It is well known that the weather in middle latitudes strongly depends on extratropical cyclones forming and developing over the North Atlantic and North Pacic re- gions. Therefore, the inuence of solar activity and related phenomena on the cyclone genesis and intensication in these regions is of substantial interest for the investiga- tors of solar-climate relationships. Macdonald and Roberts (1960) and Roberts and Olson (1973) showed that the win- tertime low-pressure troughs at the 300 mb isobaric level in the North Pacic region tend to deepen more strongly if preceded by geomagnetic or auroral activity. Schuurmans and Oort (1969) considered the variations of the 500 mb level heights after strong solar ares and found the pressure ∗ Corresponding author. Fax: +7-812-428-72-89. E-mailaddress: vereten@SV2135.spb.edu (S. Veretenenko). decrease predominating at polar and subpolar latitudes (mainly over oceans) and the pressure increase at lower lat- itudes. Wilcox et al. (1974) showed the tropospheric trough area characterized by the vorticity index reaches a mini- mum 1 day after the passing of the sector boundary of the interplanetary magnetic eld. Olson et al. (1975) revealed the increase of the vorticity index at the 500 mb level re- lated to solar ares with its consequent decrease during the geomagnetic disturbances caused by these ares. Tinsley et al. (1989), and Tinsley and Deen (1991) found vorticity decreases, predominating at the latitudes 40–65 ◦ N over oceans, associated with Forbush-decreases of the galactic cosmic rays. However, the physical mechanism of solar activity eects on weather phenomena remains unclear. It is suggested that a signicant part in the transfer of the solar variability to the lower atmosphere may be played by charged particles of solar and galactic origin, mainly protons, with energies 1364-6826/$ - see front matter c 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2003.11.005