Challenges in measuring winter precipitation: Advances in combining microwave remote sensing and surface observations

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dc.contributor.author von Lerber, Annakaisa
dc.date.accessioned 2018-01-15T08:32:10Z
dc.date.available 2018-01-15T08:32:10Z
dc.date.issued 2018-01
dc.identifier.isbn 978-952-336-045-7
dc.identifier.issn 0782-6117
dc.identifier.uri http://hdl.handle.net/10138/231104
dc.description.abstract Globally, snow influences Earth and its ecosystems in several ways by having a significant impact on, e.g., climate and weather, Earth radiation balance, hydrology, and societal infrastructures. In mountainous regions and at high latitudes snowfall is vital in providing freshwater resources by accumulating water within the snowpack and releasing the water during the warm summer season. Snowfall also has an impact on transportation services, both in aviation and road maintenance. Remote sensing instrumentation, such as radars and radiometers, provide the needed temporal and spatial coverage for monitoring precipitation globally and on regional scales. In microwave remote sensing, the quantitative precipitation estimation is based on the assumed relations between the electromagnetic and physical properties of hydrometeors. To determine these relations for solid winter precipitation is challenging. Snow particles have an irregular structure, and their properties evolve continuously due to microphysical processes that take place aloft. Hence also the scattering properties, which are dependent on the size, shape, and dielectric permittivity of the hydrometeors, are changing. In this thesis, the microphysical properties of snowfall are studied with ground-based measurements, and the changes in prevailing snow particle characteristics are linked to remote sensing observations. Detailed ground observations from heavily rimed snow particles to openstructured low-density snowflakes are shown to be connected to collocated triple-frequency signatures. As a part of this work, two methods are implemented to retrieve mass estimates for an ensemble of snow particles combining observations of a video-disdrometer and a precipitation gauge. The changes in the retrieved mass-dimensional relations are shown to correspond to microphysical growth processes. The dependence of the C-band weather radar observations on the microphysical properties of snow is investigated and parametrized. The results apply to improve the accuracy of the radar-based snowfall estimation, and the developed methodology also provides uncertainties of the estimates. Furthermore, the created data set is utilized to validate space-borne snowfall measurements. This work demonstrates that the C-band weather radar signal propagating through a low melting layer can significantly be attenuated by the melting snow particles. The expected modeled attenuation is parametrized according to microphysical properties of snow at the top of the melting layer. fi
dc.language.iso en fi
dc.publisher Finnish Meteorological Institute fi
dc.relation.ispartofseries Finnish Meteorological Institute Contributions 143 fi
dc.subject remote sensing fi
dc.subject radar fi
dc.subject snowfall fi
dc.subject precipitation microphysics fi
dc.subject surface observations fi
dc.title Challenges in measuring winter precipitation: Advances in combining microwave remote sensing and surface observations fi
dc.type Thesis fi

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