The 2021 Pacific Northwest heat wave and associated blocking: meteorology and the role of an upstream cyclone as a diabatic source of wave activity

Although heat waves account for more premature deaths in the Australian region than any other natural disaster, an understanding of their dynamics is still incomplete. The present study identifies the dynamical mechanisms responsible for heat waves in southeastern Australia using 10-day backward trajectories computed from the ERA-Interim reanalyses. Prior to the formation of a heat wave, trajectories located over the south Indian Ocean and over Australia in the lower and midtroposphere ascend diabatically ahead of an upper-level trough and over a baroclinic zone to the south of the continent. These trajectories account for 44% of all trajectories forming the anticyclonic upper-level potential vorticity anomalies that characterize heat waves in the region. At the same time, trajectories located over the south Indian Ocean in the lower part of the troposphere descend and aggregate over the Tasman Sea. This descent is accompanied by a strong adiabatic warming. A key finding is that the temperatures are raised further through diabatic heating in the boundary layer over eastern Australia but not over the inner Australian continent. From eastern Australia, the air parcels are advected southward as they become incorporated into the near-surface anticyclone that defines the heat wave. In contrast to past studies, the importance of cloud-diabatic processes in the evolution of the midlatitude large-scale flow and the role of adiabatic compression in elevating the near-surface temperatures is emphasized. Likewise, the role of the local surface sensible heat fluxes is deemphasized.

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Astrosclereids In Needles Of Old-Growth Douglas-Fir Trees

Microscopy and Microanalysis ◽

10.1017/s1431927600019528 ◽

1999 ◽

Vol 5 (S2) ◽

pp. 1240-1241

Author(s):

M. Apple ◽

A. Soeldner ◽

R. Hamill ◽

K. Tiekotfer

Keyword(s):

Pacific Northwest ◽

Cell Walls ◽

Douglas Fir ◽

Old Growth ◽

Mesophyll Cells ◽

Mesophyll Tissue ◽

The Pacific ◽

And Function ◽

Development Structure

Old-growth Douglas-fir trees in the Pacific Northwest are venerable giants that often live for 500 years and reach heights of over 75 meters. Their needles are relatively ephemeral and small but have the important role of interacting with the atmosphere in order to transpire and photosynthesize. Within the photosynthetic mesophyll tissue of Douglas-fir needles, there are large, non-living cells with lignified secondary cell walls that are known as astrosclereids. Apparent channels in the secondary wall may provide a route for exchange or transport of materials between the astrosclereid lumen and mesophyll cells or the vascular cylinder. Astrosclereids may be involvev d in storage of secondary metabolites such as tannin and may develop in response to fungi, mistletoe, or other pathogens. More knowledge is needed about the development, structure and function of astrosclereids.Needles were collected from sapling and old-growth Douglas-fir, Pseudotsuga menziesii, (Mirb.) Franco, trees at the Wind River Canopy Crane in Carson, Washington and from three sites in the Cascade Mountains of Oregon in 1997 and 1998.

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Northern Eurasian Heat Waves and Droughts

Journal of Climate ◽

10.1175/jcli-d-13-00360.1 ◽

2014 ◽

Vol 27 (9) ◽

pp. 3169-3207 ◽

Cited By ~ 101

Author(s):

Siegfried D. Schubert ◽

Hailan Wang ◽

Randal D. Koster ◽

Max J. Suarez ◽

Pavel Ya. Groisman

Keyword(s):

Soil Moisture ◽

Heat Wave ◽

Extreme Events ◽

Decadal Variability ◽

Heat Waves ◽

Precipitation Variability ◽

Northern Eurasia ◽

Temperature And Precipitation ◽

Warming World

Abstract This article reviews the understanding of the characteristics and causes of northern Eurasian summertime heat waves and droughts. Additional insights into the nature of temperature and precipitation variability in Eurasia on monthly to decadal time scales and into the causes and predictability of the most extreme events are gained from the latest generation of reanalyses and from supplemental simulations with the NASA Goddard Earth Observing System model, version 5 (GEOS-5). Key new results are 1) the identification of the important role of summertime stationary Rossby waves in the development of the leading patterns of monthly Eurasian surface temperature and precipitation variability (including the development of extreme events such as the 2010 Russian heat wave); 2) an assessment of the mean temperature and precipitation changes that have occurred over northern Eurasia in the last three decades and their connections to decadal variability and global trends in SST; and 3) the quantification (via a case study) of the predictability of the most extreme simulated heat wave/drought events, with some focus on the role of soil moisture in the development and maintenance of such events. A literature survey indicates a general consensus that the future holds an enhanced probability of heat waves across northern Eurasia, while there is less agreement regarding future drought, reflecting a greater uncertainty in soil moisture and precipitation projections. Substantial uncertainties remain in the understanding of heat waves and drought, including the nature of the interactions between the short-term atmospheric variability associated with such extremes and the longer-term variability and trends associated with soil moisture feedbacks, SST anomalies, and an overall warming world.

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Role of watering practices in large-scale urban planning strategies to face the heat-wave risk in future climate

Urban Climate ◽

10.1016/j.uclim.2016.11.001 ◽

2018 ◽

Vol 23 ◽

pp. 287-308 ◽

Cited By ~ 19

Author(s):

M. Daniel ◽

A. Lemonsu ◽

V. Viguié

Keyword(s):

Urban Planning ◽

Heat Wave ◽

Large Scale ◽

Future Climate ◽

Planning Strategies

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Prediction of Flash Droughts over the United States

Journal of Hydrometeorology ◽

10.1175/jhm-d-19-0221.1 ◽

2020 ◽

Vol 21 (8) ◽

pp. 1793-1810

Author(s):

Kingtse C. Mo ◽

Dennis P Lettenmaier

Keyword(s):

United States ◽

Soil Moisture ◽

High Temperature ◽

Pacific Northwest ◽

Heat Wave ◽

Late Summer ◽

The United States ◽

Late Spring ◽

The North ◽

June July

AbstractWe examine reforecasts of flash droughts over the United States for the late spring (April–May), midsummer (June–July), and late summer/early autumn (August–September) with lead times up to 3 pentads based on the NOAA second-generation Global Ensemble Forecast System reforecasts version 2 (GEFSv2). We consider forecasts of both heat wave and precipitation deficit (P deficit) flash droughts, where heat wave flash droughts are characterized by high temperature and depletion of soil moisture and P deficit flash droughts are caused by lack of precipitation that leads to (rather than being the cause of) high temperature. We find that the GEFSv2 reforecasts generally capture the frequency of occurrence (FOC) patterns. The equitable threat score (ETS) of heat wave flash drought forecasts for late spring in the regions where heat wave flash droughts are most likely to occur over the north-central and Pacific Northwest regions is statistically significant up to 2 pentads. The GEFSv2 reforecasts capture the basic pattern of the FOC of P-deficit flash droughts and also are skillful up to lead about 2 pentads. However, the reforecasts overestimate the P-deficit flash drought FOC over parts of the Southwest in late spring, leading to large false alarm rates. For autumn, the reforecasts underestimate P-deficit flash drought occurrence over California and Nevada. The GEFSv2 reforecasts are able to capture the approximately linear relationship between evaporation and soil moisture, but the lack of skill in precipitation forecasts limits the skill of P-deficit flash drought forecasts.

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