This was soon followed by others: Viivi Russak in 1990 "Trends of solar radiation, cloudiness and atmospheric transparency during recent decades in Estonia", and Beate Liepert in 1994 "Solar radiation in Germany — Observed trends and an assessment of their causes".
比如Viivi Russak在1990年的“爱沙尼亚近几十年来的太阳辐射、云量、大气透明度的趋势”，和Beate Liepert在1994年的“德国的太阳辐射——观测到的趋势以及造成原因的估计”。