One of the most important problem in the climate research is the quality of data. Long series of reliable climatological data are required in climatological studies on the natural climate variability and the effect of anthropogenic influences on recent climate. However, high quality climatological data seldom exist because in reality many types of disturbances can cause apparent changes which complicate and sometimes even hide the true climatic signal in the time series. Therefore, it is recommended that besides routine quality control, the homogeneity testing of data be evaluated before performing climatic studies (Toumenvirta and Alexandersson, 1997). Several techniques have been developed for detecting inhomogeneities in time series of weather elements. Formerly, non-parametric models have been developed (Sneyers, 1990, 1999) and used for testing the homogeneity of a time series of observation and detecting the climate change signal. During the last decade techniques for data homogenization are continuously developed (Alexandersson, 1986, 1995; Alexandersson and Moberg, 1997; Szentimrey, 1995, 1997, 1999; Easterling and Peterson, 1995). Some tests depend on metadata while the others are purely statistical and may be used for homogeneity testing the series where station history are poorly documented or metadata are totally missing. It is therefore increasingly need for an intercomparison study of different methods to enable climatologists to compare the results emerging from different methods and, finally, choose the most appropriate one.
The international seminar on the homogenization of surface climatological data organized by the Hungarian Meteorological Service and supported by the WMO and the NCTD every two years, since 1996, in Budapest was a good framework for exchange of knowledge and practice of various homogenization methods.

The objective of our study was the homogeneity testing of air temperature series of annual and seasonal means at 14 stations in Romania. These stations are the most used in climatic studies in Romania as they are long and continuous and, uniformly distributed over the country's territory. The selected period was 1900-1997 and the analysis was performed for seasonal and annual series.
We have used two different methods for testing the homogeneity of these series and finally the results have been compared. These methods are the Standard Normal Homogeneity Test (SNHT) developed by Alexandersson (1986, 1995) and Alexandersson and Moberg (1997) and, the Multiple Analysis of Series for Homogenization (MASH) developed by Szentimrey (1995, 1997, 1999).

The SNHT is a parametric test assuming the hypothesis of normality of the series and using neighboring stations to create a reference series to identify non-homogeneities in the time series of the candidate station. This test is used to detect single, double shift or linearly developing differences between the candidate and the reference station. We have used the SNHTW software developed at the Danish Meteorological Institute.
The MASH method was developed in the Hungarian Meteorological Service. This test can detect and adjust possible break points and shifts through mutual comparison of series within the same climatic area. The candidate series is chosen from the available series and the remaining series are considered as reference series. The optimal weighting for constructing the reference series is determined by minimizing the variance of the difference series (Szentimrey, 1999). MASH is a multiple break points detection procedure which takes into account the significance and the efficiency of the test.

We present here the results obtained after proceeding the MASH and SNHT homogeneity tests.

- for the annual temperature mean both MASH and SNHT detect the same break point year which is 1927
- MASH detects also other break points which depend on the assumption of examination (i.e., ref. series is homogeneous or non-homogeneous) and on the selection of station group for constructing the reference series
- for the seasonal temperature means MASH and SNHT tests do not detect the same break point years, except for the winter
- the correction coefficients applied for adjusting the series are slightly different ranging between +/- 0.6 for both cases
- using these two homogenization methods we have obtained 2 sets of homogeneous annual and seasonal temperature series; they do not differ significantly and they can be used both optionally in climatological studies

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