Changes In Cyclone Activity Research Articles

Spatial and Temporal Patterns of Chloride Deposition in Southern Sweden

Monthly bulk deposition of chloride at 49 stations in Southern Sweden between 1989 and 1995 was used to produce quarterly and annual deposition maps through ordinary block kriging. Generally, deposition decreases from the west coast and eastward and displays a large annual variation, governed by the frequency and intensity of midlatitude cyclones. The 1st quarter dominates the temporal pattern all years except 1992. The 4th quarter is the second most important and the 2nd and 3rd quarters have generallylow deposition. The spatial deposition maximum was often displaced from the west coast to the western fringe of the South Swedish highland, due to orographic enhancement of precipitation. On the western rise of the highland, deposition almost entirely co-variates with precipitation. On the west coast and in the eastern part of Southern Sweden, thetemporal pattern is a more complex result of precipitation and frequency of strong westerlies. Comparing the quarterly total dataset with precipitation and frequency of westerly gales shows that both the 3rd and 4th quarters have higher mean precipitation than the 1st quarter, but lower deposition, while the second quarter has substantially lower precipitation but almost equal deposition to the 3rd quarter. The frequency of westerly gales shows a clearer, linear relationship to quarterly deposition. The 1st quarter has the highest variability in deposition and precipitation as well as in frequency of westerly gales. The importance of single highlysalt laden cyclones to the annual deposition is obvious in the 1st quarter of 1993. Changes in cyclone activity due to climate change is therefore of vital importance for the chemical characteristics of the midlatitude atmosphere.

Possible connection between surface winds, solar activity and the Earth's magnetic field

RECORDS of 14C in tree rings provide a proxy for changes in solar activity on timescales of decades to centuries1,2. Here I report an association between Maunder-type solar cycles recorded in tree rings and fluctuations in surface wind intensity on a roughly 200-year timescale over a period of about 2,000 years in the mid-Holocene. The wind record is preserved as changes in the thickness of varved sediments in Elk Lake, Minnesota, which contain a large aeolian component. Changes in cyclonic activity and tropospheric winds have been reported1–5 to occur in this region a few days after strong coronal mass ejections (CMEs); increases of up to 7% in zonal flow have been reported5 at an altitude of ~ 300 m after strong CMEs in winter. The implication of this association is that century-scale changes in surface winds over Minnesota were the long-term (Maunder-scale) counterpart of short-term (daily) changes in winds after CMEs. The weak magnetic field strength of the Earth at this time6,7 might be relevant to a possible mechanism for the association.

Monthly variability of satellite‐derived cyclonic activity for the southern hemisphere winter

AbstractA satellite‐derived climatology of cloud vortices for the Southern Hemisphere winter (June to September) indicates that significant within‐season changes occur in the areal frequencies of extratropical depressions. This variability is found to be most strongly associated with the climatic frontal zones, while on a zonally‐averaged basis, the semi‐annual oscillation of the circumpolar vortex appears to dominate the latitudinal changes in cyclonic activity between June and September. Surface‐atmosphere interactions evidently play a key role in the wintertime circulation at middle and high latitudes. Cyclogenesis over the Southern Oceans is observed to be linked closely to the baroclinity associated with the Oceanic Polar Front, while on a regional scale, the presence of a time‐averaged zone of in situ cyclogenesis over sub‐antarctic latitudes of the South Pacific is found to be augmented by the influence of the unique winter season sea ice regime in that sector.