HI Ana-Maria,

Thanks for attaching the graph to clarify your questions. In the graph, is it monthly averages being plotted on the Y-axis? I am assuming they are in my answer (even though the idea would be same even if they were not).

The higher atmospheric pressure values during the winter in Focsani are caused by the relatively cold conditions experienced in this region compared to summer.

Since Cold air is more dense than relatively warm air, it has a tendency to sink, relatively, and thus has a higher pressure than warm air. From this, it can be gleaned that the winter months would have an higher average atmospheric pressure than in the summer.

In mid latitude continental regions, such as Focsani, Romania, monthly average atmospheric pressure is usually characterized by seasonal variations, with the lowest values occurring in winter (when its colder) and highest in summer. Although periods of precipitation, and therefore fluctuations in atmospheric pressure, occur throughout the year in Focsani, these fluctuations would most likely not produce a signal on a time series plotting monthly averages. It would be more valuable to consider this variable using monthly averages in the context provided by your question.

Furthermore, it isn't clear if you are trying to explain the trend, but if so, a few ideas:

The trend you see would not be due to any increase in average air pressure over the period 2000-2012, but that is not to say that there was not an increase (or decrease). If the trend is what your are concerned with, I would plot the time series of monthly average for each year on the same plot. By comparing the time series of each year's monthly averages, you could see the shifts of year to year trends in order to gain an idea to whether there has been an increase or decrease. Of course, a robust quantitative analysis would have to be carried out in order to gauge the statistical significance of any such shift.

For summer is the paper...

http://rjm.inmh.ro/articole/busuioc.pdf

Thx Tivadar for the comment and for the article .

HI Ana-Maria,

Thanks for attaching the graph to clarify your questions. In the graph, is it monthly averages being plotted on the Y-axis? I am assuming they are in my answer (even though the idea would be same even if they were not).

The higher atmospheric pressure values during the winter in Focsani are caused by the relatively cold conditions experienced in this region compared to summer.

Since Cold air is more dense than relatively warm air, it has a tendency to sink, relatively, and thus has a higher pressure than warm air. From this, it can be gleaned that the winter months would have an higher average atmospheric pressure than in the summer.

In mid latitude continental regions, such as Focsani, Romania, monthly average atmospheric pressure is usually characterized by seasonal variations, with the lowest values occurring in winter (when its colder) and highest in summer. Although periods of precipitation, and therefore fluctuations in atmospheric pressure, occur throughout the year in Focsani, these fluctuations would most likely not produce a signal on a time series plotting monthly averages. It would be more valuable to consider this variable using monthly averages in the context provided by your question.

Furthermore, it isn't clear if you are trying to explain the trend, but if so, a few ideas:

The trend you see would not be due to any increase in average air pressure over the period 2000-2012, but that is not to say that there was not an increase (or decrease). If the trend is what your are concerned with, I would plot the time series of monthly average for each year on the same plot. By comparing the time series of each year's monthly averages, you could see the shifts of year to year trends in order to gain an idea to whether there has been an increase or decrease. Of course, a robust quantitative analysis would have to be carried out in order to gauge the statistical significance of any such shift.

Hi Dear Ana

Thanks to Mr. Andrew for his full answer. In addition, the mentioned graph is related to Mean Surface Pressure. However, In higher geopotential levels such as 500 hPa we observe the diverse pattern of Inter Tropical Convergence Zone (ITCZ) in summer and winter months along the mid latitudes of northern hemisphere. Consequently, we should consider the annual shifts of ITCZ to reach a correct trend analysis.

Good Luck

This is all very interesting, and I come at this question with complete ignorance, for which I apologise. However, although the temperature effect is presumably there to an extent, it seems too large an effect on its own. For example, if you take peak summer temperature as 20 K warmer than peak winter, the pressure difference due to temperature (and hence density) should be about 7% (~20/300) whereas the effect you see is an order of magnitude lower. I think it's important when you consider these factors, that it holds together QUANTITATIVELY. After all, we are supposed to be physicists! So, to me it seems that there is still an effect to be explained.

It depends on temperatures degree for ex. In iraq there is a high degree of temperatures in july compare with december

It depends on temperatures degree for ex. In iraq there is a high degree of temperatures in july compare with december