Temperature of polar corona of the sun during the last 50 years (1952-2001)

We investigate the variations of temperature in the polar corona using the long-term observations of intensity of the coronal lines FeXIV 530.3 nm and FeX 637.4 nm at the high latitudes during 1952-2001. We composed a combined series of the green and red intensities for 1952-2001, using the Kislovodsk data as basis, inserting missing data from other observatories. The mean monthly coronal intensities KI5303 and KI6374 have been calculated in the sunspot (0degrees-45degrees) and in the high-latitude (45degrees-90degrees) zones. We found that the average intensity of KI5303 decreased 1.5 times, while the intensity of KI6374 increased 1.7 times at the high-latitude zone during the last 50 years. The ratio KI6374/KI5303 shows the 22-year cycle of temperature of the polar corona. The average value of KI6374 /KI5303 more than doubled during 1957-2001. It corresponds to a decrease of average coronal temperature at the high latitudes by 0.2 (.) 10(6) K. We argue that a decrease of coronal temperature is connected with the increase (doubling) of the area of the polar zones A(pz) occupied by unipolar magnetic fields (Makarov et al., 2002) and, probably, with an increase of the area of polar coronal holes.