Analysis of Observed Discrepancies in Precipitation Measurements in the Complex Terrain of East-Iceland

• Main Author: Þórarinsson, Páll Ágúst
• Format: Bachelor Thesis
• Language: English
• Published: Uppsala universitet, Luft-, vatten- och landskapslära 2021
• Subjects: Precipitation; precipitation measurements; weather observation; complex terrain; weather regimes; Iceland; Nederbörd; nederbördmätningar; väder observationer; komplex terräng; vädersituationen; Island; Meteorology and Atmospheric Sciences; Meteorologi och atmosfärforskning; Irminger Sea; Norwegian Sea; North Atlantic
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-444558

Spatial distribution of precipitation in complex terrain can be very uneven and there are many factors to consider when studying it. The goal of this study was such a problem; to analyse the difference in observed annual precipitation in the complex terrain of Seyðisfjörður, a fjord in East-Iceland. The study was carried out in three parts. First, it was investigated if there was a systematic difference between measurement methods using different instruments. Second, the effect of the complex terrain on the spatial distribution of precipitation was investigated, and lastly if this observed difference could be linked to any certain kind of weather regimes. To simplify the analysis, only liquid precipitation was included in the data set. In Seyðisfjörður there are three divergently located precipitation gauges of three different types and set up. At the Icelandic Meteorological Office in Reykjavík the same type of gauges are co-located with the exact same set up as in Seyðisfjörður. A statistical analysis of those measurements showed that there is a systematic undercatch in tipping bucket gauges compared to weighted capacity and standard accumulation gauges. However, the difference is insignificant in size compared to the observed difference in the complex terrain. The complex terrain was found to highly affect the airflow and therefore the spatial distribution of precipitation, as it almost only rains in synoptic wind directions with an easterly component (measured at a mountain station). To connect events where there was a great difference in precipitation measurements to the synoptic weather situation over the North-Atlantic, a projection connecting the geostrophic and local winds in the fjord was made. It showed that great precipitation as well as when great differences are observed, during two kind of weather regimes. One where a low pressure is travelling along the North-Atlantic storm track to the Norwegian Sea. The other were a low pressure is stationed southwest or west of Iceland in the Irminger Sea ...