100 research outputs found
Arctic Mission Benefit Analysis: impact of sea ice thickness, freeboard, and snow depth products on sea ice forecast performance
Assimilation of remote-sensing products of sea ice thickness (SIT) into sea
ice–ocean models has been shown to improve the quality of sea ice forecasts.
Key open questions are whether assimilation of lower-level data products such
as radar freeboard (RFB) can further improve model performance and what
performance gains can be achieved through joint assimilation of these data
products in combination with a snow depth product. The Arctic Mission Benefit
Analysis system was developed to address this type of question. Using the
quantitative network design (QND) approach, the system can evaluate, in a
mathematically rigorous fashion, the observational constraints imposed by
individual and groups of data products. We demonstrate the approach by
presenting assessments of the observation impact (added value) of different
Earth observation (EO) products in terms of the uncertainty reduction in a
4-week forecast of sea ice volume (SIV) and snow volume (SNV) for three
regions along the Northern Sea Route in May 2015 using a coupled model of the
sea ice–ocean system, specifically the Max Planck Institute Ocean
Model. We assess seven satellite products: three real products and four
hypothetical products. The real products are monthly SIT, sea ice freeboard
(SIFB), and RFB, all derived from CryoSat-2 by the Alfred Wegener Institute.
These are complemented by two hypothetical monthly laser freeboard (LFB)
products with low and high accuracy, as well as two hypothetical monthly snow
depth products with low and high accuracy.On the basis of the per-pixel uncertainty ranges provided with the CryoSat-2
SIT, SIFB, and RFB products, the SIT and RFB achieve a much better
performance for SIV than the SIFB product. For SNV, the performance of SIT is
only low, the performance of SIFB is higher and the performance of RFB is yet
higher. A hypothetical LFB product with low accuracy (20 cm
uncertainty) falls between SIFB and RFB in performance for both SIV and SNV.
A reduction in the uncertainty of the LFB product to 2 cm yields a
significant increase in performance.Combining either of the SIT or freeboard products with a hypothetical
snow depth product achieves a significant performance increase.
The uncertainty in the snow product matters: a higher-accuracy product
achieves an extra performance gain.
Providing spatial and temporal uncertainty correlations with the
EO products would be beneficial not only for QND assessments,
but also for assimilation of the products.</p
Freezing in the Sun
When the air is very cold, water at the surface of the ocean freezes, forming sea ice. Parts of the Arctic Ocean are covered by sea ice during the entire year. Often, snow falls onto the sea ice. Despite the cold, many plants and animals can live in the Arctic Ocean, some in the water, and some even in the sea ice. Particularly, algae can live in small bubbles in the sea ice. Like other plants, algae need energy to grow. This energy comes from food and sunlight. But how can the sunlight reach these little algae living inside the sea ice? From the sun, the light must pass through the atmosphere, the snow, and finally the sea ice itself. In this article, we describe how ice algae can live in this special environment and we explain what influences how much light reaches the algae to make them grow
Sensitivities and uncertainties in a coupled regional atmosphere-ocean-ice model with respect to the simulation of Arctic sea ice
An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 58 (2011): 173-185, doi:10.1016/j.dsr.2010.12.002.Unprecedented summer-season sampling of the Arctic Ocean during the period 2006−2008 makes
possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins.
In comparison to observations from 1992−1999, LFW content relative to a salinity of 35 in the layer
from the surface to the 34 isohaline increased by 8400 ± 2000 km3 in the Arctic Ocean (water depth
greater than 500m). This is close to the annual export of freshwater (liquid and solid) from the Arctic
Ocean reported in the literature.
Observations and a model simulation show regional variations in LFW were both due to changes
in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a
mean freshening of the water column above this depth, associated with an increased net sea ice melt
and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic
Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in
LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a
quarter of the salinity contribution, and non-linear effects due to both factors were negligible.This work was supported by the Co-Operative Project “The
North Atlantic as Part of the Earth System: From System Comprehension to Analysis of Regional
Impacts” funded by the German Federal Ministry for Education and Research (BMBF) and by the European Union Sixth Framework Programme project DAMOCLES (Developing Arctic Modelling and
Observing Capabilities for Long-term Environment Studies), contract number 018509GOCE
Testing variational estimation of process parameters and initial conditions of an earth system model
We present a variational assimilation system around a coarse resolution Earth System Model (ESM) and apply it for estimating initial conditions and parameters of the model. The system is based on derivative information that is efficiently provided by the ESM's adjoint, which has been generated through automatic differentiation of the model's source code. In our variational approach, the length of the feasible assimilation window is limited by the size of the domain in control space over which the approximation by the derivative is valid. This validity domain is reduced by non-smooth process representations. We show that in this respect the ocean component is less critical than the atmospheric component. We demonstrate how the feasible assimilation window can be extended to several weeks by modifying the implementation of specific process representations and by switching off processes such as precipitation
Future extreme events in European climate: an exploration of regional climate model projections
Modeling decadal variability of the Baltic Sea. Part 1: Reconstructing atmospheric surface data for the period 1902-1998
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