Year: 2004
Type: dissertation
Abstract: A study was made of the climate of Finland during the period since regular organised meteorological observations were recorded.Special attention was given to the reliability and homogeneity of the data.In the Finnish mean temperature and precipitation series there are synchronized, nation-wide homogeneity breaks that bias the original series.These discontinuities must be adjusted before performing studies of climatic changes.The Standard Normal Homogeneity Test (SNHT) was used for homogeneity testing of climatic time series.A homogeneity testing and adjustment methodology was developed, in which SNHT and metadata (information on data) are used complementarily to produce homogenous series.In addition, homogeneity of area-averages based on a large number of stations was examined.It turned out that the use of the First Difference Method enables one to maximise the number of stations and to calculate unbiased area-averages without relative homogeneity testing and adjustment.Statistical tests show that there has been a significant increase in the Finnish annual and spring (March-April-May) mean temperatures during the last 150 years or so.The spring temperature increase has been quite linear and it is more significant than the annual mean temperature increase.From the 1970s onwards there has been a rapid increase in temperature, especially during wintertime.A strong time-mean westerly wind, related to a positive North Atlantic Oscillation Index, was observed in connection with recent warm winters.Atmospheric circulation indices defined by zonal and meridional sea level pressure differences, along with sea level pressure and cloud cover anomalies were used to build a multiple linear regression model for the Fennoscandian Diurnal Temperature Range (DTR).During the period 1910-95 the model explains from 53% (winter) to 80% (summer) of the variation in DTR, and reproduces the statistically significant decreasing trend at an annual level.Cloud cover is the dominant predictor, while circulation provides substantial improvement in explanation.The decrease of DTR can be explained primarily by cloud cover increase and a strengthening of the westerly flow bringing more humid marine air masses into Fennoscandia.
Source: Työväentutkimus Vuosikirja
Author: Heikki Tuomenvirta
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
OpenAlex ID: W566872472