DETAILED  REPORT  FOR  THE  COST-­‐STSM-­‐ES1005-­‐13486,  14.IV-­‐05.V.2013,  INSTITUTE  OF  ATMOSPHERIC  PHYSICS  and  CHARLES  UNIVERSITY,  PRAGUE    

I. Abstract  The STSM was carried out for the period indicated in the application approved by

COST: April 14 - May 5, 2013. The work during the stage was splitted in data preparation, data analysis, mapping and evaluation of the results. The study is focused on data not only at European scale, as proposed in the primary application, but included the entire Northern Hemisphere, aiming at a better understanding of the possible influence of solar activity upon the continental scale. Sea surface pressure and 500 hPa geopotential height data were analysed. The main results indicate that the solar activity affects especially the North Atlantic region and the position of the Icelandic low center.

II. Purpose of the STSM The aim of the STSM was to analyse solar activity effects on the frequency and the

intensity of the main pressure centres influencing the European continent (Icelandic Low, Azores High, Mediteranean Low, Eurasian High). We considered that solar impact on atmospheric circulation is a possible primary signature of solar variability in the Earth climate. These results could be seen as a continuation of previous studies relating solar activity to atmospheric circulation in Europe (Huth et al., 2008, Barriopedro et al., 2008, Kuroda et al., 2005 etc.).

III. Work description during the STSM a. Construction of data-base for geopotential height at 500 hPa and sea surface level

pressure for the Northern Hemisphere between 30˚N and the North Pole from NCEP/NCAR (5 deg. lat/lon gridpoints)

b. Correlation analysis at monthly and seasonal level for each gridpoint for geopotential height at 500 hPa and sea surface level on the one hand, and the solar activity on other hand;

c. Pearson correlation analysis for each gridpoint between the solar activity and 1 month lagged geopotential height at 500 hPa (eg. December 1948 solar activity with January 1949 geopotential height) at monthly and seasonal level.

d. Serial autocorrelation check using Durbin-Watson test for all regions with significant Pearson correlation coefficients;

e. Separation between low and high solar activity months using sunspot number between 1948 and 2012.

f. Computing the differences between the level of 500 hPa geopotential height and sea level pressure in high solar months and low solar months.

g. Running a t-test for the difference of mean under independence; h. Mapping the main results; i. Identification of the lowest gridpoint sea surface pressure in the North Atlantic (from

all years) and assuming this point as the centre of Islandic low in both low and high solar months;

k. Creating frequency maps showing the position of the centre of Islandic low in the North Atlantic region in low and high solar years;

l. Bibliographical research. IV. Main results obtained a. Correlations between sunspot number and geopotential height: - Pearson correlation at monhly scale indicates no clear pattern and it is assumed for

possible randomness;

- generally the correlation is highest for the period between February and April. - the above results are not infuenced by autocorrelation for these months; - the North Atlantic region, the main domain of the Icelandic Low, presents a persistent

negative correlation between solar activity and 500 hPa geopotential height; - the Pearson seasonal correlation proves that the possible link between solar activity

(as reflected by sunspot number) and geopotential height is restricted to the cold season (December-January-February) and dissapears entirely during the other seasons;

- the Pearson seasonal correlation with 1 month lag (eg. nov-dec-jan for the sunspot number with dec-jan-feb geopotential height, below) shows better correlations the the direct ones with the same pattern (Fig. 1);

- the second region with significant correlations can be seen in Pacific.  

   

Fig. 1 - Pearson correlation between direct (left) and 1 month lagged (right) winter's 500 hPa geopotential height and solar activity (white-no signficant correlation; light red - significant positive correlations at 10%; dark red -positive significant correlation at 5%; light blue - significant negative

correlations at 10%; dark blue - significant regative correlation at 5%)  2. Differences between geopotential height during high and low solar months: - the North Atlantic region presents the highest significant differences of geopotential

height between high and low solar activity; - variations are rather small in terms of absolute values (50 m at monthly level and 30 m

at seasonal level for geopotential height; ± 3 hPa for sea surface pressure at seasonal level); - in the North Atlantic region the geopotential height is lower during high solar

conditions suggesting a deepening of the Islandic Low in such conditions (eg. Fig. 2 - Latitudinal differences between high and low solar conditions at seasonal scale in the North Atlantic region 0-40˚long W);

- for sea surface pressure a similar spatial pattern as for geopotential height could be identified; in comparison with 500 hPa geopotential height, other limited areas of significant differences apear in the region of Aleutian low and Central Asia (fig. 3).

 

   Fig. 2 - Mean difference (in m) between winter's 500 hPa geopotential height during high and low solar

months (left) and regions where this difference is statistically significant(white-no signficant correlation; light red - significant positive correlations at 10%; dark red -positive significant correlation at 5%; light blue -

significant negative correlations at 10%; dark blue - significant regative correlation at 5%) after t-test verification (right)

 

   

Fig. 3 - Mean difference (in hPa) between winter's sea level pressure during high and low solar months (left) and regions where this difference is statistically significant(white-no signficant correlation; light red -

significant positive correlations at 10%; dark red -positive significant correlation at 5%; light blue - significant negative correlations at 10%; dark blue - significant regative correlation at 5%) after t-test verification (right)

3. Influence of the solar activity on the position of the Islandic low: - the Islandic low has a main domain of development concentrated on the south of

Greenland and another one on the ENE of Island; - in the low solar months the depression tends to be centered more noth-easterly than in

high solar months when its developments shifts to the south-west.  

   

Fig. 4 - Spatial relative frequency (%) of Islandic Low center during high(left) and low(right)solar months

 - in the solar maximum months the depression is centred between 61-65˚N and 26-35˚W

while in the solar minimum months is centred between 56-60˚N and 36-45˚W: there is a shift of about 1000 km between the two phases of solar activity (fig. 4).

 V. Future colaboration with the host institution Considering that Charles University (Czech Republic) and Alexandru Ioan Cuza

University (Romania) are both members in the European Erasmus programme, teaching and/or research stays are possible for both the applicant and the host of the STSM. The exchange will be planned during the coming two years. We intend to extend our collaboration on the basis of the Erasmus programme; in the scientific program, we plan, among others, to include more solar activity proxies.

VI. Foreseen publications/articles resulting from the STSM We plan to submit one or two articles to renowned peer-reviewed journals with the

following subjects: 1. Influence of solar activity upon the pressure field in Northern Hemisphere's troposphere.

2. Differences between the main position of the Islandic low during high and low solar activity.

VII. Other comments I benefited of a very nice accommodation in a beautiful town. Professor Huth and his

collaborators were very helpful, which contributed to an efficient implementation of this mission.

References: 1. Barriopedro, D., R. Garcıa-Herrera, R. Huth, 2008, Solar modulation of Northern Hemisphere

winter blocking, J. Geophys. Res., 113, D14118, doi:10.1029/2008JD009789. 2. Radan Huth, LuciePokorna, Josef Bochnıcek, Pavel Hejda, Combined solar and QBO effects

on the modes of low-frequency atmospheric variability in the Northern Hemisphere, Journal of Atmospheric and Solar-Terrestrial Physics 71 (2009) 1471–1483.

3. Kuroda, Y. and K. Kodera, 2005, Solar cycle modulation of the Southern Annular Mode, Geophys. Res. Letters, 33, L13802, doi: 10.1029/2005GL022516.