A network-based detection scheme for the jet stream core
The polar and subtropical jet streams are strong upper-level winds with a crucial influence on weather throughout the Northern Hemisphere midlatitudes. In particular, the polar jet is located between cold arctic air to the north and warmer subtropical air to the south. Strongly meandering states the...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-02-01
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| Series: | Earth System Dynamics |
| Online Access: | http://www.earth-syst-dynam.net/8/75/2017/esd-8-75-2017.pdf |
| Summary: | The polar and subtropical jet streams are strong upper-level winds
with a crucial influence on weather throughout the Northern Hemisphere
midlatitudes. In particular, the polar jet is located between cold arctic
air to the north and warmer subtropical air to the south. Strongly
meandering states therefore often lead to extreme surface weather.
<br><br>
Some algorithms exist which can detect the 2-D (latitude and longitude) jets'
core around the hemisphere, but all of them use a minimal threshold to
determine the subtropical and polar jet stream. This is particularly
problematic for the polar jet stream, whose wind velocities can change
rapidly from very weak to very high values and vice versa.
<br><br>
We develop a network-based scheme using Dijkstra's shortest-path algorithm
to detect the polar and subtropical jet stream core. This algorithm not only
considers the commonly used wind strength for core detection but
also takes wind direction and climatological latitudinal position into
account. Furthermore, it distinguishes between polar and subtropical jet,
and between separate and merged jet states.
<br><br>
The parameter values of the detection scheme are optimized using simulated
annealing and a skill function that accounts for the zonal-mean jet stream
position (Rikus, 2015). After the successful optimization process,
we apply our scheme to reanalysis data covering 1979–2015 and calculate
seasonal-mean probabilistic maps and trends in wind strength and position of
jet streams.
<br><br>
We present longitudinally defined probability distributions of the positions
for both jets for all on the Northern Hemisphere seasons. This shows that
winter is characterized by two well-separated jets over Europe and Asia (ca.
20° W to 140° E). In contrast, summer normally has a
single merged jet over the western hemisphere but can have both merged and
separated jet states in the eastern hemisphere.
<br><br>
With this algorithm it is possible to investigate the position of the jets'
cores around the hemisphere and it is therefore very suitable to analyze jet
stream patterns in observations and models, enabling more advanced model-validation. |
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| ISSN: | 2190-4979 2190-4987 |