Miscellaneous

19 January 2009 - A few weeks ago, the Royal Meteorological Institute of Belgium (RMI) published the results of its study on the climate evolution in Belgium. "Eye on the Climate" covers the period 1833-2007 and is a well-balanced and thorough report on the various climate parameters and the possible factors that can influence the climate in Belgium. There does not seem to be an English version of this report, but it is highly recommended to take that French dictionary and read the entire text!

Probably the most important conclusions concerning the weather parameters are:

• Since 1900, the temperature in Belgium has increased by 2°C. However, this occured in 2 steps, i.e. around 1910 (+0,9°C) and at the end of the 1980's (+1,1°C).
• Though there are, since 1990, more heatwaves (and an increasing number of "summerdays"), their number is not higher than in the 1940's. The stepwise changes are noticeable again. The droughtperiods have not become longer.
• There is no significant evolution in the yearly number of precipitation days, nor in the amount and intensity (precipitation per hour) of thunderstorms in Uccle. ...if the vulnerability of the urban areas has increased due to thunderstorms, then this is probably the result of other factors like e.g. the building-concentration and the impenetrability of the soil. ...
• Since the 1980's, it snows considerably less. The first frost days occur almost 2 weeks later (since 1950), and the last frost days at least a week earlier (since 1980). Again there are stepwise changes.
• The average windspeed has decreased (-10% since the early 1980's), and neither in the number of storms nor in their intensity an increase has been found (since the last 20 years).
• The yearly number of hours with sunshine is very variable, but doesn't show any trend during the last 120 years.

Most important remarks concerning the climate factors are:

• There remains a big uncertainty on the reaction of the amount of clouds on the temperature increase caused by the increased greenhouse gases.
• From a study on aerosols, of which the amount is very probably controlled by the amount of atmospheric pollution, and the amount of sunshine, it appears that the heating of the earth's surface due to the increased solar radiation (post 1985) can at least partially explain the high temperatures. ... So we can't point only to the increasing greenhouse gases and in particular CO2 for being responsible for the recent temperature increase, also the increased solar radiation has to be taken into account. ...
• The variations in solar radiation are small (0,1°C per 0,1% variation in solar radiation), but can not be neglected when it comes to a correct estimation of the influence of greenhouse gases and aerosols.
• Longterm temperature reconstructions show a "Medieval warm period" (around 1100) and a "small ice age" around 1600 that can be likely explained by changes in the incoming solar radiation on top of the atmosphere.
• ... We would like to eliminate a often heard misunderstanding. The greenhouse effect is a natural phenomenon. Water vapour is without a doubt the most important greenhouse gas amongst the greenhouse gases,...
• Cosmic rays are responsible for the ionization in the upper layers of the troposphere and probably have an influence on the cloud cover.

On climate models:

• The obvious and irregular variability of the atmospheric parameters, and the sensitivity to the initial conditions, are the two visible aspects of the dynamics typical of the atmospheric models (chaotic dynamics). It is important to emphasize that this is not a consequence of our limited knowledge and incomplete description of the laws governing our atmosphere, but a true characteristic of the spectrum of possible dynamical systems obeying this kind of laws. ... One of the essential properties of these equations is that they are inherently non-linear. ... One of the biggest problems in this context is the precize modelling of all the exchanges between the different elements of the climate system. ... This leads to the question how well and how far in the future climate can be predicted, in view of the limited horizon of weather predictions....
• Numerous studies have shown that the oceans and the ice are playing a crucial role in climate dynamics, over longer timescales than those of the atmosphere. ... Another example of behaviour related to the presence of non-linear climate elements is the possible interruption of the so-called thermohaline circulation. ... The change of such a parameter can result in climate transiting from one condition to another, changing the statistical properties of the system entirely. ... It appears that the presence of modelling errors can have important consequences on the predictions. For example, a transition to a regime different than that which is being studied, can be missing. ...
• So, it looks like , at the moment, not all uncertainties related to our future climate have been accounted for and that the error margin of future developments is bigger than the error margin claimed in the current climate reports.

New topics (at least to me):

• The temperature anomaly in the period June 2006-July 2007 may possibly indicate a new stepwise increase in temperature. Of course, more research and more of these warm periods are necessary to confirm this anomaly.
• Little attention has been paid to the connection between climate changes and changes in the geomagnetic field. ... Indeed, for the last millennium, some researchers seem to have found an apparent relationship between rapid changes in the field intensity ... and periods of global cooling in Western Europe...

Evolution of polar faculae number: Observed vs. Seeing-corrected

The polar faculae (PF) I observed the last 10 years were done from 2 different locations: From mid-1996 till mid-2000 from Texas, USA (average seeing Q=4), and for the other years from Belgium (average seeing Q=3). The number of PF seen is heavily influenced by the seeing. This is readily apparent when determining the ratio R between PF as deduced from SOHO-images with my own PF-numbers for a certain Q-value (see table underneath).

Best fit is found for the formula R = (Q-2,15)/(Q-2,85). It was decided to rescale the observed PF-numbers in order to get comparable values where Q = 3,5 all the time, i.e. PF-numbers where Q > 3,5 will be reduced, and PF-numbers where Q < 3,5 get increased. This however resulted in overcorrections during the wintermonths of 2000-2003 in Belgium, where average seeing approaches 2,85 (correction approaches infinity!). For the smoothed period May 2000 - August 2003, R = (Q-2)/(Q-2,7) was applied. The 2,7-limit gives more margin during the Belgian wintermonths, but keeping at the same time a good fit with the ratio SOHO / JJ. The original and seeing-adjusted PF-evolution can be found underneath.

It may be clear that the current PF-numbers are steadily increasing, but are still far from the activity-levels during the previous solar cycle. This implies that solar minimum may be further away than is general believed (2007 in stead of late 2006), or the PF-maximum may be lower than the previous maximum, which -according to the solar dynamo model- could mean that the upcoming solar cycle may be lower than SC23.

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