Frauenfeld, O.W., T. Zhang, and J. L. McCreight. Submitted. Climatology and variability of the 20th century Northern Hemisphere freezing/thawing index. International Journal of Climatology.
Mitchell TD, Jones PD. 2005. An improved method of constructing a database of monthly climate observations and associated high-resolution grids. International Journal of Climatology 25, 693 712.
Simmons ... A. J., P. D. Jones, V da Costa Bechtold, A. C. M. Beljaars, P. W. KÃ¥llberg, S. Saarinen, S. M. Uppala, P. Viterbo, and N. Wedi. 2004. Comparison of trends and variability in CRU, ERA-40, and NCEP/NCAR analyses of monthly-mean surface air temperature. ERA-40 Project Report Series No. 18, 38.
Willmott C.J. and K. Matsura. 2001. Terrestrial air temperature and precipitation: Monthly and annual time series (1950-1999). Newark, DE: Center for Climatic Research, Department of Geography, University of Delaware, Newark.