Milan Milenković

THE NORTH ATLANTIC OSCILLATION (NAO) AND THE WATER TEMPERATURE OF THE SAVA RIVER IN SERBIA

The data on the water temperature of the Sava in Serbia (hydrological stations Sabac and Belgrade, period 1961–2015) were used for the research, as well as the data on the surface air temperature. The temperature trends were determined and the significance (at p≤0.05 and p≤0.01) was established on the basis of the t-test. The Pearson correlation coefficient (R) was used for the calculation of the correlation. Increasing trends of the water temperature of the Sava were recorded in all cases at both stations. However, in the case of the HS Sabac, the trends for 6 months (February–April and September–November) were not statistically significant. In the case of the HS Belgrade, all the calculations (except for April) showed statistically significant increasing trends, which can be explained by anthropogenic influence. High level of correlation between the surface air temperature and the water temperature was also determined. In this research, the lowest values of R were recorded for October (0.561 for Belgrade), and on the seasonal level, for autumn (0.625 for Sabac). The research on the correlation between the water temperature of the Sava River and the NAO index showed the highest values of R for January (0.512 for HS Sabac and 0.528 for HS Belgrade). On the seasonal level, the highest values were recorded for winter (0.422 for HS Sabac and 0.432 for HS Belgrade).

FOREST FIRES IN PORTUGAL — THE CONNECTION WITH THE ATLANTIC MULTIDECADAL OSCILLATION (AMO)

The data on forest fires in Portugal in the period 1980–2015 were used in the research: the annual number of forest fires, the annual burned area and the average burned area per fire. Increasing trend of the annual number of forest fires (statistically significant at p≤0.01), non-significant increasing trend of the annual burned area and decreasing trend of the average burned area per fire (statistically significant at p≤0.01) were recorded. Portugal is the most endangered country by forest fires in comparison with the other European countries. During the research period, fires in Portugal covered 23.6% of the total burned area in five the most affected European countries (Portugal, Spain, France, Italy and Greece). In the research of the connection between forest fires and the Atlantic Multidecadal Oscillation (AMO) Pearson correlation coefficient (R) was used. Monthly, seasonal and annual values of the AMO index were used in calculations. All R values recorded for the annual number of fires were positive and statistically significant at p≤0.01. The highest values were recorded for August (0.543) and for summer (0.525). With the annual burned area all R values were also positive and the highest one on the seasonal level was for summer (0.359). With the average burned area per fire all R values were negative (−0.428 was recorded for winter). The results of the research could be applied in the fire danger forecast for periods of several months. Other climate indices should also be considered in future research.

ELECTRONS OR PROTONS: WHAT IS THE CAUSE OF FOREST FIRES IN WESTERN EUROPE ON JUNE 18, 2017?

Forest fires in Portugal (June 17–24, 2017) destroyed 64 lives and caused considerable material damage. The coronal hole CH807 and the energy region S5710 were in the geoeffective position on the Sun immediately before the outbreak of fires. In the period that preceded it, as well as at the time of the fires, increased values of the solar wind (SW) parameters (temperature, speed and density of particles) were recorded. In addition, a geomagnetic disorder was recorded. The shape and size of the burning areas, as well as the low air pressure over Portugal indicate the possibility of the effect of positively charged particles that came from the area south, i.e. southwest of Portugal. Nevertheless, it is a specific case that would have to be investigated in more detail.

Tropical temperature altitude amplification in the hiatus period (1998-2012)

In the period 1998-2012 there was a stagnation in temperature rise, despite the GHGs radiation forcing is increased (hiatus period). According to Global Circulation Models simulations, expected response on the rise of GHGs forcing is tropical temperature altitude amplification - temperature increases faster in higher troposphere than in lower troposphere. In this paper, two satellite data sets, UAH MSU and RSS, were used to test altitude temperature amplification in tropic (20°N-20°S) in the hiatus period. We compared data from satellite data sets from lower troposphere (TLT) and middle troposphere (TMT) in general and particularly for land and ocean (for UAH MSU). The results from both satellite measurements showed the presence of hiatus, i.e. slowdown of the temperature rise in the period 1998-2012 compared to period 1979-2012 (UAH MSU) and temperature fall for RSS data. Smaller increase, i.e. temperature fall over ocean showed that hiatus is an ocean phenomenon above all. Data for UAH MSU showed that temperature altitude amplification in tropic was not present either for period 1979-2012, or 1998-2012. RSS data set also do not show temperature altitude amplification either for longer (1979-2012), or for shorter period (1998-2012). RSS data for successive 15-year periods from 1979-1993 till 1998-2012 does not show tropical temperature altitude amplification and in one case negative trend is registered in TLT and in two cases in TMT. In general, our results do not show presence of temperature altitude amplification in tropic in the hiatus period. [Projekat Ministarstva nauke Republike Srbije, br. III47007]