Impacts of Subtropical Highs on Summertime Precipitation in North America

Schmidt, Daniel F.; Grise, Kevin M.

doi:10.1029/2019jd031282

Cited by 10 publications

(16 citation statements)

References 69 publications

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“…The North Pacific High Intensity index shown in Fig. 1b is based on the North Pacific Subtropical High (NPSH) strength index developed by Schmidt et al 44 , which measures the average monthly mean NCEP Reanalysis 2 SLP in a 10 × 10 box centered on the NPSH SLP centroid. See ref.…”

Section: Methodsmentioning

confidence: 99%

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Physical drivers of the summer 2019 North Pacific marine heatwave

et al. 2020

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Summer 2019 observations show a rapid resurgence of the Blob-like warm sea surface temperature (SST) anomalies that produced devastating marine impacts in the Northeast Pacific during winter 2013/2014. Unlike the original Blob, Blob 2.0 peaked in the summer, a season when little is known about the physical drivers of such events. We show that Blob 2.0 primarily results from a prolonged weakening of the North Pacific High-Pressure System. This reduces surface winds and decreases evaporative cooling and wind-driven upper ocean mixing. Warmer ocean conditions then reduce low-cloud fraction, reinforcing the marine heatwave through a positive low-cloud feedback. Using an atmospheric model forced with observed SSTs, we also find that remote SST forcing from the central equatorial and, surprisingly, the subtropical North Pacific Ocean contribute to the weakened North Pacific High. Our multi-faceted analysis sheds light on the physical drivers governing the intensity and longevity of summertime North Pacific marine heatwaves.

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Section: Methodsmentioning

confidence: 99%

“…See ref. 44 for more details. We then show anomalies of this index (hPa) relative to a 1982-2018 climatology in Fig.…”

Section: Methodsmentioning

confidence: 99%

Physical drivers of the summer 2019 North Pacific marine heatwave

et al. 2020

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“…Both approaches reveal that zonal mean widening does not imply a widening at all longitudes. For example, the southeastern United States, though in the subtropical belt, is removed from the prototypical Hadley cell-wise circulation (Staten et al 2019); there, shifts in the North Atlantic subtropical high modulate large-scale precipitation patterns (Schmidt and Grise 2019).…”

Section: E901mentioning

confidence: 99%

Tropical Widening: From Global Variations to Regional Impacts

Staten

Grise

Davis

et al. 2020

Bulletin of the American Meteorological Society

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Over the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade‒1—within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.

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“…Previous studies have shown that the NASH affects precipitation in the SE US on timescales that range from diurnal to multi‐decadal (e.g., Diem, 2006; Li et al ., 2011, 2012, 2013; Bishop et al ., 2019; Schmidt and Grise, 2019). On daily timescales, Luchetti et al .…”

Section: Introductionmentioning

confidence: 99%

“…On multi‐decadal timescales the NASH western ridge has been shown to have shifted westward between 1948 and 1977 (Li et al ., 2011) and eastward from 1978–2007 (Diem, 2013a; 2013b). Some of this variability has been linked to the influence of stationary wave trains driven by the Pacific Decadal Oscillation (Li et al ., 2011; 2013) as well as to a possible intensification and expansion of the NASH during this period (Li et al ., 2011; He et al ., 2017; Schmidt and Grise, 2019).…”

Section: Introductionmentioning

confidence: 99%

Effects of the North Atlantic Subtropical High on summertime precipitation organization in the southeast United States

Ferreira

Rickenbach

2020

Intl Journal of Climatology

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This study analyzes the effect of the location of the North Atlantic Subtropical High (NASH) western ridge on the daily variability of precipitation organization in the southeastern United States (SE US). The western side of the NASH, also known as the NASH western ridge, plays an important role in the variability of summertime precipitation in this region. In this study, the mean summertime position of the NASH western ridge was determined and used to classify each summer day during 2009–2012 into one of four quadrants. Composites of synoptic‐scale circulation and precipitation from mesoscale and isolated precipitation features (MPF and IPF) were calculated for each NASH western ridge quadrant. MPF contributed most (about 65%) of the total summertime precipitation and accounted for most of the differences between the four NASH quadrants. Domain‐averaged precipitation was highest (lowest) during NASH‐SW (NASH‐NW) when IPF (MPF) precipitation was strongest (weakest). The regionality of MPF precipitation maxima was generally associated with the location of low‐level jets and upper‐level troughs. For instance, positive MPF anomalies occurred across the SE US during NASH‐SW when the Great Plains low‐level jet turned eastward bringing moisture to fuel convection in the SE US. In contrast, IPF rain was distributed more uniformly across the SE US. Finally, this study revealed a dipole of precipitation that is controlled by the position of the NASH western ridge and its associated low‐level jets. In one extreme of the dipole NASH‐SE, periods are associated with enhanced MPF precipitation along the coast and offshore for days at a time, and suppressed MPF precipitation inland. The opposite pattern occurs during NASH‐NW when MPF precipitation is enhanced inland and suppressed along the coast and offshore.

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Impacts of Subtropical Highs on Summertime Precipitation in North America

Cited by 10 publications

References 69 publications

Physical drivers of the summer 2019 North Pacific marine heatwave

Physical drivers of the summer 2019 North Pacific marine heatwave

Tropical Widening: From Global Variations to Regional Impacts

Effects of the North Atlantic Subtropical High on summertime precipitation organization in the southeast United States

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