Vincent Courtillot教授学术报告

题    目：Persistent temperature disturbances and solar forcing

主讲人：Prof. Vincent Courtillot

时    间：6月11日14:00-16:00

地    点：215会议室

报告摘要：

In a recent series of papers, we have analyzed daily land-based
temperature
series (maximum, minimum, mean, differences between  maximum and minimum)
from
tens of meteorological stations in several  regions (Europe, USA,
Australia).
We select stations with long (100 to  300 years), homogeneous series with
almost no gap. The long-term  (decadal to centennial) evolution of
temperature
disturbances (which  display characteristic times from several days to 1-2
weeks) reveals a  clear solar signature. The secular trend of disturbances
rises from  1900 to 1950, decreases from 1950 to 1975 and then increases
again,
decreasing in the most recent decade. This trend is the same as that  found
for a number of solar indices. Our investigations reveal high  heterogeneity
and seasonality of the climate system and underlines  regional and seasonal
variations in the observed solar signature. We  compare short-term
autocorrelation properties of temperature  disturbances for different
seasons
at decadal timescales. The solar  signature appears to be significantly
stronger in Winter and in the  late Fall seasons. Intensities of
disturbances
may vary by a factor in  excess of 2. We have performed a special analysis
of
tens of station  data from two 2.5°x2.5° areas of the US North Pacific:
again
we find  that the long term evolution of temperature disturbances from 1945
to
2008 closely follows that of solar activity, with a large (30%)  modulation
compared to corresponding changes in solar irradiance. In  another study, we
have analyzed the longest (up to 300 years) series  from 3 European
stations.
We have partitioned daily temperatures and  their differences in two subsets
as
a function of high vs low solar  activity. We follow a pattern recognition
approach and demonstrate,  using the two-sample Kolmogorov-Smirnov
statistics,
that the  separation is statistically significant and robust. Differences
between the annual changes for the two classes are large (1°C). In all  of
these studies, significant solar forcing is present and may be a  rather
general feature. We speculate over possible mechanisms: these  likely
involve
cloudiness modulated by cosmic rays, solar activity,  the EUV part of the
solar
flux, the downward ionosphere-earth current  density…