What Controls the Probability Distribution of Local Wave Activity in the Midlatitudes?

Valva, Claire; Nakamura, Noboru

doi:10.1029/2020jd034501

Cited by 3 publications

(3 citation statements)

References 42 publications

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“…(Only for Figure 2b we use hourly data.) The diagnostic framework follows the prescription of HN16 and HN17 (see also N. Nakamura & Huang, 2018; Valva & Nakamura, 2021, and Supporting Information of the present article). To quantify the jet stream's meander and identify blocks we use LWA, which measures the meridional displacement of quasigeostrophic potential vorticity (QGPV), q , from a zonally symmetric reference state

A(\lambda ,\phi ,z,t)=-\frac{a}{\mathrm{cos}\,\phi }{\int }_{0}^{{\Delta}\phi }{q}_{e}\left(\lambda ,\phi +{\phi }^{\prime },z,t\right)\mathrm{cos}\left(\phi +{\phi }^{\prime }\right)d{\phi }^{\prime },

where ( λ , ϕ , z , t ) specifies longitude, latitude, pressure pseudoheight and time, a is planetary radius and q e is the QGPV field relative to its reference state value at ϕ

{q}_{e}\left(\lambda ,\phi +{\phi }^{\prime },z,t\right)=q\left(\lambda ,\phi +{\phi }^{\prime },z,t\right)-{q}_{\text{REF}}(\phi ,z,t).

…”

Section: Data and The Wave Activity Diagnostic Formalismmentioning

confidence: 99%

“…(Only for Figure 2b we use hourly data.) The diagnostic framework follows the prescription of HN16 and HN17 (see also N. Nakamura & Huang, 2018;Valva & Nakamura, 2021, and Supporting Information of the present article). To quantify the jet stream's meander and identify blocks we use LWA, which measures the meridional displacement of quasigeostrophic potential vorticity (QGPV), q, from a zonally symmetric reference state…”

Section: Data and The Wave Activity Diagnostic Formalismmentioning

confidence: 99%

See 1 more Smart Citation

The 2021 Pacific Northwest Heat Wave and Associated Blocking: Meteorology and the Role of an Upstream Cyclone as a Diabatic Source of Wave Activity

Neal

Huang

Nakamura

2022

Geophysical Research Letters

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The heat wave that enveloped the Pacific Northwest from late June through early July 2021 delivered unprecedented temperatures to the normally cool region -108°F (42°C) in Seattle, 116°F (47°C) in Portland -and claimed over 1,000 lives mostly in British Columbia (AON, 2021). One preliminary study puts it in a 1-in-1,000 years event category (Philip et al., 2021). As with most heat waves in the midlatitudes (Fang & Lu, 2020;Pfahl & Wernli, 2012), the event was associated with an anomalous behavior of the jet stream (atmospheric blocking).In this study, we address (a) the dynamics that led to the formation of an unusually strong blocking anticyclone and (b) how the blocking anticyclone drove extreme surface temperatures during this particular event. Both topics have been studied extensively in a broader context. For example, backward trajectory studies (e.g., Zschenderlein et al., 2019) identified subsidence in the free troposphere, as well as the prolonged downward solar radiation, as a key ingredient for extreme surface heat inside a persistent blocking anticyclone. Soil moisture feedback was also a significant contributor to past major heat events in Europe (Black et al., 2004;Whan et al., 2015). We will show that during the Pacific Northwest event of 2021 the formation of an upper-level blocking preceded the extreme surface temperatures by 2-3 days, demonstrating a top-down thermodynamic control of blocking on the surface temperatures. The warm air mass inside the block was created upstream and its arrival capped convection over land and raised surface temperatures to an unusual level.The mechanism of block formation is a major topic in its own right. Synoptic eddies migrating along the jet stream have long been thought of as feeding and maintenance mechanisms of blocks (Luo,

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A(\lambda ,\phi ,z,t)=-\frac{a}{\mathrm{cos}\,\phi }{\int }_{0}^{{\Delta}\phi }{q}_{e}\left(\lambda ,\phi +{\phi }^{\prime },z,t\right)\mathrm{cos}\left(\phi +{\phi }^{\prime }\right)d{\phi }^{\prime },

where ( λ , ϕ , z , t ) specifies longitude, latitude, pressure pseudoheight and time, a is planetary radius and q e is the QGPV field relative to its reference state value at ϕ

{q}_{e}\left(\lambda ,\phi +{\phi }^{\prime },z,t\right)=q\left(\lambda ,\phi +{\phi }^{\prime },z,t\right)-{q}_{\text{REF}}(\phi ,z,t).

…”

Section: Data and The Wave Activity Diagnostic Formalismmentioning

confidence: 99%

“…(Only for Figure 2b we use hourly data.) The diagnostic framework follows the prescription of HN16 and HN17 (see also N. Nakamura & Huang, 2018;Valva & Nakamura, 2021, and Supporting Information of the present article). To quantify the jet stream's meander and identify blocks we use LWA, which measures the meridional displacement of quasigeostrophic potential vorticity (QGPV), q, from a zonally symmetric reference state…”

Section: Data and The Wave Activity Diagnostic Formalismmentioning

confidence: 99%

The 2021 Pacific Northwest Heat Wave and Associated Blocking: Meteorology and the Role of an Upstream Cyclone as a Diabatic Source of Wave Activity

Neal

Huang

Nakamura

2022

Geophysical Research Letters

Self Cite

View full text Add to dashboard Cite

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“…Interestingly, the LWA bias estimated from the tracer model tends to be more zonally extended while the LWA bias in large ensembles is more regional. This is likely because the passive tracer, unlike PV, does not feedback on advecting winds or transient eddies (e.g., storm tracks) and thus induces a dynamical inconsistency in eddy‐mean flow interactions and jet meandering (Haynes et al., 2007; Valva & Nakamura, 2021).…”

Section: Resultsmentioning

confidence: 99%

Constraining the Varied Response of Northern Hemisphere Winter Circulation Waviness to Climate Change

Nie

Chen

et al. 2023

Geophysical Research Letters

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The extratropical westerly circulation exhibits frequent latitudinal displacements on the synoptic timescale, manifesting as Rossby waves with alternating ridges and troughs. Under certain circumstances, a large meandering of the westerly jet induces stagnant weather patterns such as atmospheric blocking, resulting in regional temperature extremes or severe air pollution (Buehler et al., 2011;Pfahl & Wernli, 2012;W. Sun et al., 2019). It was hypothesized that Arctic amplification, the enhanced surface warming in the Arctic region relative to lower latitudes under increasing greenhouse gases, slows down the midlatitude westerly flow, which, in turn, causes an increase in circulation waviness and associated weather extremes (Francis & Vavrus, 2012). While there is observational evidence for the coincidence between Arctic amplification and increasing waviness (Francis et al., 2017;Vavrus, 2018), the observed multidecadal trends in waviness are rather weak and largely obscured by internal variability of the climate system (Blackport & Screen, 2020). Using large ensembles from multiple climate models, Smith et al. ( 2022) conclude a robust, weak winter circulation response to future Arctic sea ice loss, but models also exhibit substantial internal variability, for which even a 100-member ensemble may be insufficient to detect robust midlatitude circulation response to Arctic warming (Peings et al., 2021;L. Sun et al., 2022). Moreover, the weakened midlatitude jet stream due to Arctic warming can be offset by tropical upper-tropospheric warming that strengthens the jet, producing a net effect of small decreases in waviness at the end of the 21st century, albeit with considerable model spread (

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Jet Stream Meandering in the Northern Hemisphere Winter: An Advection–Diffusion Perspective

Nie

Zhang

2022

Journal of Climate

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Large meridional excursions of a jet stream are conducive to blocking and related midlatitude weather extremes, yet the physical mechanism of jet meandering is not well understood. This paper examines the mechanisms of jet meandering in boreal winter through the lens of a potential vorticity (PV)-like tracer advected by reanalysis winds in an advection-diffusion model. As the geometric structure of the tracer displays a compact relationship with PV in observations and permits a linear mapping from tracer to PV at each latitude, jet meandering can be understood by the geometric structure of tracer field that is only a function of prescribed advecting velocities. This one-way dependence of tracer field on advecting velocities provides a new modeling framework to quantify the effects of time mean flow versus transient eddies on the spatiotemporal variability of jet meandering. It is shown that the mapped tracer wave activity resembles the observed spatial pattern and magnitude of PV wave activity for the winter climatology, interannual variability, and blocking-like wave events. The anomalous increase in tracer wave activity for the composite over interannual variability or blocking-like wave events is attributed to weakened composite mean winds, indicating that the low-frequency winds are the leading factor for the overall distributions of wave activity. It is also found that the tracer model underestimates extreme wave activity, likely due to the lack of feedback mechanisms. The implications for the mechanisms of jet meandering in a changing climate are also discussed.

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What Controls the Probability Distribution of Local Wave Activity in the Midlatitudes?

Cited by 3 publications

References 42 publications

The 2021 Pacific Northwest Heat Wave and Associated Blocking: Meteorology and the Role of an Upstream Cyclone as a Diabatic Source of Wave Activity

The 2021 Pacific Northwest Heat Wave and Associated Blocking: Meteorology and the Role of an Upstream Cyclone as a Diabatic Source of Wave Activity

Constraining the Varied Response of Northern Hemisphere Winter Circulation Waviness to Climate Change

Jet Stream Meandering in the Northern Hemisphere Winter: An Advection–Diffusion Perspective

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