Variability of daily course of selected bioclimatic indices in Kołobrzeg during summer-season over the period 1981–1990

Abstract

Changes in biometeorological conditions are of special significance at health resorts. The recognition of a daily cyclicity in this respect therefore leads to more effective planning of climatic therapy at coastal sites. The purpose of the paper is to analyze and evaluate daily variability to biothermal conditions in Kołobrzeg over the period 1981-1990. Calculations were based on average values for air temperature, dewpoint temperature, cloud cover, wind speed and air pressure at 0:00, 3:00, 6:00, 9:00, 12:00, 15:00, 18:00 and 21:00 UTC. The period of analysis covers June, July and August. Bioclimatic conditions were evaluated in terms of bioclimatic indices, these being: simple: - Insulation Predicted (Iclp, in clo) - predicted value for the thermal insulation of clothing that is necessary to assure a person thermal comfort; - Maximal Activity Level (MHR, in Wnr2) - the limit value for activity that does not provoke a rise in heart rate in the given meteorological conditions above 90 beats per minute. - based on human heat balance: - an index illustrating the thermal stimuli felt subjectively by a person and caused by the ambient environment in advance of the activation of adaptation processes; STI depending on both ambient conditions as regards temperature, solar radiation, wind and humidity and man-environment heat exchange, and hence indicating the thermal load formed in the air layer surrounding an outer layer of clothing: thermal impacts of the environment are expressed by reference to mean radiant temperature, while the physiological response of an organism is represented by net heat storage; - Physiological Strain (PhS, dimensionless) - indicates which physiological processes adapt the human organism to given outdoor conditions; Solar radiation absorbed by a nude man (R', in Wm-2) - as dependent on the intensity and structure of solar radiation, the elevation of the sun, ground albedo, body-to-Sun orientation and insulation. Calculations were carried out using BioKlima 2.5 software. The research applied the arithmetic mean, linear regression, polynomial functions and frequency of occurrence in respect of STI and PhS across specific ranges. To evaluate the variability to ranges of fluctuations, amplitudes of indices were calculated. The 3-hour data were approximated by a fourth-order polynomial function, while the maximal and minimal values of air temperature and STI were estimated. Also determined were the average daily courses to be noted for bioclimatic indices in the presence of different (arctic, polar-maritime, polar-continental, and tropical) masses of air. Calculations reveal some variability to the daily cyclicty of meteorological elements and bioclimatic indices. This variability concerns both values of elements and indices and special features characterising daily courses. It was possible to note a marked, if not significant, upward trend for cloud cover around noon, this reducing the solar stimuli reaching an organism. Moreover, decreased wind speed and increased air temperature during daytime hours were to be observed. The analysis shows that values for the Subjective Temperature Index and Physiological Strain increase around noon, this pointing to the appearance of heat stress. These results correspond to growing values for solar radiation absorbed by a nude man (R') at noon, this confirming the influence of solar radiation in increasing heat load. The extreme values for temperature and cloud cover show that differences between minimal and maximal values became greater, while the minimal values were noted earlier. STI and PhS indicate that cool and moderate cold stress dominate during the night hours, while heat stress appears at noon. The most comfortable conditions occur at 6 a.m. and 3 and 6 p.m. Taking into consideration air masses, the best conditions are shown to be observed under arctic and polar-maritime air masses. The polar-continental and tropical masses represent an obstacle to active forms of recreation.