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M. Bentsen, G. Evensen, H. Drange, and A. D. Jenkins

Abstract

When setting up global ocean circulation models one faces the problem of including the Arctic Ocean where the traditional spherical coordinate system has a singularity at the pole. In addition, in regional model applications one has to deal with open boundaries where assumptions are made about the normally poorly known boundary conditions. Here an analytical reversible coordinate transformation on a sphere that preserves the orthogonality and the shape of infinitesimal figures is presented. Starting from a standard spherical coordinate system, the transformation is able to map the North and South Poles to two arbitrary locations of the earth and this is readily done with the aid of a conformal mapping in the extended complex plane. The resulting coordinate system will have enhanced resolution along the geodesic curve between the new poles. Examples are given where the transformation is used to strongly increase the resolution in a particular region of interest in the model domain.

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M. A. Jenkins, W. C. Wong, K. Higuchi, and J. L. Knox

Abstract

This paper examines the 27-yr record of precipitation measurements at Ocean Weather Station “P” (50°N, 145°W). The credibility of the rainfall observations is assessed, and the testing of certain extraordinary features of the fall and winter seasonal precipitation time series is outlined. Using the portion of the record established to be close to “ground truth” (1954–1967), the authors have statistically related present weather observations to seasonal precipitation amounts at Ocean Weather Station “P.” With this approach, the authors have reproduced the first half (1954–1967) and predicted the second half (1969–1980) of the precipitation time series to compare to observations. Precipitation is physically estimated by determining the vertical moisture convergence at Ocean Weather Station “P” and comparing the relative consistency of the moisture convergence time series to the contemporaneous seasonal rate of measured precipitation. The analysis suggests that the Ocean Weather Station “P” record of measured precipitation is a substantial improvement over previous estimates of precipitation in the northeast Pacific for the period between 1954 and 1967, but that the second half of the record, particularly during the early 1970s, remains questionable. Reliable rainfall estimates along with measurements for the 27-yr record are given to aid studies dealing with energy balance calculations and the verification of oceanic precipitation generated by global climate models.

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Stephan T. Kral, Joachim Reuder, Timo Vihma, Irene Suomi, Kristine F. Haualand, Gabin H. Urbancic, Brian R. Greene, Gert-Jan Steeneveld, Torge Lorenz, Björn Maronga, Marius O. Jonassen, Hada Ajosenpää, Line Båserud, Phillip B. Chilson, Albert A. M. Holtslag, Alastair D. Jenkins, Rostislav Kouznetsov, Stephanie Mayer, Elizabeth A. Pillar-Little, Alexander Rautenberg, Johannes Schwenkel, Andrew W. Seidl, and Burkhard Wrenger

Abstract

The Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer Program (ISOBAR) is a research project investigating stable atmospheric boundary layer (SBL) processes, whose representation still poses significant challenges in state-of-the-art numerical weather prediction (NWP) models. In ISOBAR ground-based flux and profile observations are combined with boundary layer remote sensing methods and the extensive usage of different unmanned aircraft systems (UAS). During February 2017 and 2018 we carried out two major field campaigns over the sea ice of the northern Baltic Sea, close to the Finnish island of Hailuoto at 65°N. In total 14 intensive observational periods (IOPs) resulted in extensive SBL datasets with unprecedented spatiotemporal resolution, which will form the basis for various numerical modeling experiments. First results from the campaigns indicate numerous very stable boundary layer (VSBL) cases, characterized by strong stratification, weak winds, and clear skies, and give detailed insight in the temporal evolution and vertical structure of the entire SBL. The SBL is subject to rapid changes in its vertical structure, responding to a variety of different processes. In particular, we study cases involving a shear instability associated with a low-level jet, a rapid strong cooling event observed a few meters above ground, and a strong wave-breaking event that triggers intensive near-surface turbulence. Furthermore, we use observations from one IOP to validate three different atmospheric models. The unique finescale observations resulting from the ISOBAR observational approach will aid future research activities, focusing on a better understanding of the SBL and its implementation in numerical models.

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