Northern hemisphere extratropical tropospheric planetary waves and their low-frequency variability: Their vertical structure and interaction with transient eddies and surface thermal contrasts

2010 ◽  
pp. 149-179 ◽  
Author(s):  
Hisashi Nakamura ◽  
Takafumi Miyasaka ◽  
Yu Kosaka ◽  
Koutarou Takaya ◽  
Meiji Honda
Keyword(s):  
Northern Hemisphere ◽  
Vertical Structure ◽  
Low Frequency ◽  
Planetary Waves ◽  
Low Frequency Variability

scholarly journals Eddy-Induced Growth Rate of Low-Frequency Variability and Its Mid- to Late Winter Suppression in the Northern Hemisphere

2014 ◽  
Vol 71 (7) ◽  
pp. 2281-2298 ◽  
Author(s):  
Hong-Li Ren ◽  
Fei-Fei Jin ◽  
Jong-Seong Kug
Keyword(s):  
Northern Hemisphere ◽  
Storm Track ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Surface Friction ◽  
Late Winter ◽  
Wind Maximum ◽  
Low Frequency Variability ◽  
Storm Track Activity ◽  
Effect Of Surface

Abstract Synoptic eddy and low-frequency flow (SELF) feedback plays an important role in reinforcing low-frequency variability (LFV). Recent studies showed that an eddy-induced growth (EIG) or instability makes a fundamental contribution to the maintenance of LFV. To quantify the efficiency of the SELF feedback, this study examines the spatiotemporal features of the empirical diagnostics of EIG and its associations with LFV. The results show that, in terms of eddy vorticity forcing, the EIG rate of LFV is generally larger (smaller) in the upper (lower) troposphere, whereas, in terms of eddy potential vorticity forcing, it is larger in the lower troposphere to partly balance the damping effect of surface friction. The local EIG rate shows a horizontal spatial distribution that corresponds to storm-track activity, which tends to be responsible for maintaining LFV amplitudes and patterns as well as sustaining eddy-driven jets. In fact, the EIG rate has a well-defined seasonality, being generally larger in cold seasons and smaller in the warmest season, and this seasonality is stronger in the Northern Hemisphere than in the Southern Hemisphere. This study also reveals a mid- to late winter (January–March) suppression of the EIG rate in the Northern Hemisphere, which indicates a reduced eddy feedback efficiency and may be largely attributed to the eddy kinetic energy suppression and the midlatitude zonal wind maximum in the midwinter of the Northern Hemisphere.

scholarly journals Interannual Subtropical Indian Ocean Variability due to Long Baroclinic Planetary Waves

2020 ◽  
Vol 33 (16) ◽  
pp. 6765-6791
Author(s):  
Christopher C. Chapman ◽  
Bernadette M. Sloyan ◽  
Terence J. O’Kane ◽  
Matthew A. Chamberlain
Keyword(s):  
Indian Ocean ◽  
Feature Tracking ◽  
Model Simulation ◽  
Low Frequency ◽  
Phase Speed ◽  
Heat Fluxes ◽  
Planetary Waves ◽  
Near Surface ◽  
South Indian ◽  
Low Frequency Variability

AbstractLow-frequency variability in the south Indian Ocean is studied by analyzing 200 years of output from a fully coupled climate model simulation. At time scales of 2–10 years, the variability is dominated by westward-propagating features that form on the eastern side of the basin. Using feature tracking and clustering, the spatiotemporal characteristics and preferred pathways of the propagating features are identified and studied in detail. By comparison of the phase speed and vertical structure of the propagating anomalies identified by the feature tracking with linear theory, we conclude that these features are likely mode 1 or 2 baroclinic planetary waves. The effects of this low-frequency variability on the climate system is investigated. By analysis of the mixed-layer temperature budget, it is shown that at particular geographic locations, the propagating features can substantially modify the near-surface ocean and induce significant fluxes of heat into the atmosphere. In turn, these heat fluxes can drive a coherent atmospheric response, although this response does not appear to feed back onto the ocean. Finally, we discuss the implications for the interannual climate predictability.

scholarly journals The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability

2012 ◽  
Vol 8 (2) ◽  
pp. 765-786 ◽  
Author(s):  
B. Christiansen ◽  
F. C. Ljungqvist
Keyword(s):  
Confidence Intervals ◽  
Northern Hemisphere ◽  
Little Ice Age ◽  
Low Frequency ◽  
Medieval Warm Period ◽  
Warm Period ◽  
Ice Age ◽  
Frequency Noise ◽  
Reference Period ◽  
Low Frequency Variability

Abstract. We present two new multi-proxy reconstructions of the extra-tropical Northern Hemisphere (30–90° N) mean temperature: a two-millennia long reconstruction reaching back to 1 AD and a 500-yr long reconstruction reaching back to 1500 AD. The reconstructions are based on compilations of 32 and 91 proxies, respectively, of which only little more than half pass a screening procedure and are included in the actual reconstructions. The proxies are of different types and of different resolutions (annual, annual-to-decadal, and decadal) but all have previously been shown to relate to local or regional temperature. We use a reconstruction method, LOCal (LOC), that recently has been shown to confidently reproduce low-frequency variability. Confidence intervals are obtained by an ensemble pseudo-proxy method that both estimates the variance and the bias of the reconstructions. The two-millennia long reconstruction shows a well defined Medieval Warm Period, with a peak warming ca. 950–1050 AD reaching 0.6 °C relative to the reference period 1880–1960 AD. The 500-yr long reconstruction confirms previous results obtained with the LOC method applied to a smaller proxy compilation; in particular it shows the Little Ice Age cumulating in 1580–1720 AD with a temperature minimum of −1.0 °C below the reference period. The reconstructed local temperatures, the magnitude of which are subject to wide confidence intervals, show a rather geographically homogeneous Little Ice Age, while more geographical inhomogeneities are found for the Medieval Warm Period. Reconstructions based on different subsets of proxies show only small differences, suggesting that LOC reconstructs 50-yr smoothed extra-tropical NH mean temperatures well and that low-frequency noise in the proxies is a relatively small problem.

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