Jet Strength Research Articles

Impacts of Latent Energy and Snow Fall Speed on a Wintertime Midlatitude Cyclone

AbstractThis study aimed to understand the impacts of latent energy as well as snow fall speeds on precipitation properties and synoptic‐scale storm characteristics of a wintertime midlatitude cyclone. Simulations of a potent winter storm that impacted the Rocky Mountains and northern Great Plains of the United States in February 2017 were performed using the Weather Research and Forecasting model with latent heating or cooling from individual microphysical processes systematically turned off and fall speeds adjusted by ±50%. Results indicated substantial impacts on the microphysical characteristics of the simulated storm to fall speed, cooling from sublimation, and warming from deposition. The impacts of cooling and warming were manifested as differences in accumulated snowfall. Increased (decreased) fall speeds led to smaller (larger) ice crystals and total mass, resulting in offsetting effects on the precipitation flux, and thus minimal impacts on snowfall and large‐scale characteristics of the storm. Warming and cooling associated with deposition and sublimation, respectively, impacted the synoptic‐scale dynamics, whereby removing warming from deposition resulted in an increased meridional temperature gradient near the jet stream, thus increasing the jet strength and causing it to be more westerly with less curvature aloft. This in turn limited upper‐level divergence, creating a weaker surface low and shifting the precipitation shield southward. The opposite occurred with the removal of latent cooling due to sublimation. This study highlights the potential importance of latent energy associated with ice sublimation and deposition and fall speeds in the larger‐scale characteristics of winter storms.

The Role of Tropical, Midlatitude, and Polar Cloud-Radiative Changes for the Midlatitude Circulation Response to Global Warming

AbstractPrevious studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMIP-like simulations. To this end, we study global warming simulations from the ICON model run with the cloud-locking method and prescribed sea surface temperatures, which isolate the impact of changes in atmospheric cloud-radiative heating. Tropical cloud changes dominate the global cloud impact on the 850 hPa zonal wind, jet strength, and storm track responses across most seasons and regions. For the jet shift, a more diverse picture is found. In the annual mean and DJF, tropical and midlatitude cloud changes contribute substantially to the poleward jet shift in all regions. The poleward jet shift is further supported by polar cloud changes across the Northern Hemisphere but not in the Southern Hemisphere. In JJA, the impact of regional cloud changes on the jet position is small, consistent with an overall small jet shift during this season. The jet shift can be largely understood via the anomalous atmospheric cloud-radiative heating in the tropical and midlatitude upper troposphere. The circulation changes are broadly consistent with the influence of cloud-radiative changes on upper-tropospheric baroclinicity and thus the mean potential energy available for conversion into eddy kinetic energy. Our results help to explain the jet response to global warming and highlight the importance of tropical and midlatitude cloud-radiative changes for this response.

Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO

AbstractNorthern Europe and the UK experienced an exceptionally warm and wet winter in 2019/20, driven by an anomalously positive North Atlantic Oscillation (NAO). This positive NAO was well forecast by several seasonal forecast systems, suggesting that this winter the NAO was highly predictable at seasonal lead times. A very strong positive Indian Ocean dipole (IOD) event was also observed at the start of winter. Here we use composite analysis and model experiments, to show that the IOD was a key driver of the observed positive NAO. Using model experiments that perturb the Indian Ocean initial conditions, two teleconnection pathways of the IOD to the north Atlantic emerge: a tropospheric teleconnection pathway via a Rossby wave train travelling from the Indian Ocean over the Pacific and Atlantic, and a stratospheric teleconnection pathway via the Aleutian region and the stratospheric polar vortex. These pathways are similar to those for the El Niño Southern Oscillation link to the north Atlantic which are already well documented. The anomalies in the north Atlantic jet stream location and strength, and the associated precipitation anomalies over the UK and northern Europe, as simulated by the model IOD experiments, show remarkable agreement with those forecast and observed.

An Evaluation of the Large‐Scale Atmospheric Circulation and Its Variability in CESM2 and Other CMIP Models

AbstractThe Community Earth System Model 2 (CESM2) is the latest Earth System Model developed by the National Center for Atmospheric Research in collaboration with the university community and is significantly advanced in most components compared to its predecessor (CESM1). Here, CESM2's representation of the large‐scale atmospheric circulation and its variability is assessed. Further context is providedthrough comparison to the CESM1 large ensemble and other models from the Coupled Model Intercomparison Project (CMIP5 and CMIP6). This includes an assessment of the representation of jet streams and storm tracks, stationary waves, the global divergent circulation, the annular modes, the North Atlantic Oscillation, and blocking. Compared to CESM1, CESM2 is substantially improved in the representation of the storm tracks, Northern Hemisphere (NH) stationary waves, NH winter blocking and the global divergent circulation. It ranks within the top 10% of CMIP class models in many of these features. Some features of the Southern Hemisphere (SH) circulation have degraded, such as the SH jet strength, stationary waves, and blocking, although the SH jet stream is placed at approximately the correct location. This analysis also highlights systematic deficiencies in these features across the new CMIP6 archive, such as the continued tendency for the SH jet stream to be placed too far equatorward, the North Atlantic westerlies to be too strong over Europe, the storm tracks as measured by low‐level meridional wind variance to be too weak and a lack of blocking in the North Atlantic sector.

The Tropical Easterly Jet over Africa, its representation in six reanalysis products, and its association with Sahel rainfall

AbstractThis paper compares the characteristics of the Tropical Easterly Jet (TEJ) and upper‐level winds in six reanalysis products, compares them with soundings at seven West African locations, examines the relationship between Sahel rainfall and the TEJ, and examines factors influencing the TEJ. The jet characteristics assessed by MERRA2, NCEP 1, JRA 55, and ERA 5 are similar. CFSR and 20th Century Reanalysis are outliers in nearly every analysis, overestimating wind speeds by as much as 25 to 40% compared to other reanalyses. Over the period 1948 to 2014, the correlation between rainfall and TEJ magnitude is .72. Arguments based on observations and modelling studies provide evidence that on interannual scales changes in the TEJ are not forced by rainfall, that large‐scale factors drive the TEJ. Potential mechanisms are discussed for a causal relationship such that a strong jet leads to high rainfall. However, further modelling efforts are needed to conclusively determine whether the TEJ/Sahel rainfall link is a result of common forcing factors. The factors that appear to control jet strength include sea‐surface temperature (SST) contrast between the central equatorial Pacific and central equatorial Indian Ocean (correlation of −.64), SST contrast between the central equatorial and the southern subtropical Indian Ocean (correlation of −.39), the latitude of the shift between upper‐tropospheric easterlies and westerlies in the Southern Hemisphere (correlation of −.84 at 150 hPa), and the intensity of the Southern Hemisphere westerlies (correlation of +.52 at 200 hPa). This suggests considerable control on the TEJ by extra‐tropical circulation in the Southern Hemisphere.

The influence of tidal jet current – Ocean wave interaction on the embayed beach processes

Many embayed beaches are formed by barriers that block embayments to create barrier-enclosed estuaries. These embayed beaches are characterized by strong tidal jets that drain the estuaries through a tidal inlet, often debouching at one end. A field study was conducted on Buffalo Beach in Mercury Bay (Waikato, New Zealand) to study wave energy changes caused by the ebb tidal jet. Acoustic Doppler Current Meter observations showed that during peak ebb jet flow, a decrease in wave height occurred along the beach sites that were in close proximity to the ebb jet. A DELFT3D hydrodynamic and wave model was used to further show that wave height variance was due to the jet current causing shoaling and refraction between the central beach and inlet adjacent southern beach. The resulting wave energy focused along the southern beach, diverged along the central beach and increased the alongshore radiation stress gradient. Under modeled storm conditions within the bay, when wave heights exceed 1.5 m, the jet was found to increase spreading and overall jet width. The jet orientation was also deflected shoreward towards the inlet adjacent headland. The radiation stresses driving alongshore transport became increasingly dominant with increased wave height, suggesting that alongshore sediment mobility increases substantially during a storm event due to the presence of the jet. Implications are that jet strength and orientation play a role in embayed beach rotation.

Testing the Limits and Breakdown of the Nonacceleration Theorem for Orographic Stationary Waves

AbstractThe nonacceleration theorem states that the torque exerted on the atmosphere by orography is exactly balanced by the convergence of momentum by the stationary waves that the orography excites. This balance is tested in simulations with a stationary wave model and with a dry, idealized general circulation model (GCM), in which large-scale orography is placed at the latitude of maximum surface wind speed. For the smallest mountain considered (maximum height H = 0.5 m), the nonacceleration balance is nearly met, but the damping in the stationary wave model induces an offset between the stationary eddy momentum flux (EMF) convergence and the mountain torque, leading to residual mean flow changes. A stationary nonlinearity appears for larger mountains (H ≥ 10 m), driven by preferential deflection of the flow around the poleward flank of the orography, and causes further breakdown of the nonacceleration balance. The nonlinearity grows as H is increased, and is stronger in the GCM than in the stationary wave model, likely due to interactions with transient eddies. The midlatitude jet shifts poleward for H ≤ 2 km and equatorward for larger mountains, reflecting changes in the transient EMFs, which push the jet poleward for smaller mountains and equatorward for larger mountains. The stationary EMFs consistently force the jet poleward. These results add to our understanding of how orography affects the atmosphere’s momentum budget, providing insight into how the nonacceleration theorem breaks down; the roles of stationary nonlinearities and transients; and how orography affects the strength and latitude of eddy-driven jets.

Use of synthetic jet to a fully-active flapping foil for power extraction enhancement

The power extraction performance of a fully-active flapping foil with synthetic jet is numerically investigated in this work. An elliptic airfoil with ratio of 8, which is placed in a two-dimensional laminar flow, is adopted to extract power from the flow. The foil implements the imposed translational and rotational motions synchronously. A pair of synthetic jets with the same frequency and strength is integrated into the upper and lower surfaces of flapping foil. As a result, the flow field around the foil could be affected by the synthetic jets greatly. At the Reynolds number of 1000 and the pitching axis location of half chord, the effects of the jet strength, the inclined angle between the jet direction and the chord line, as well as the phase angle between the synthetic jets and the flapping motion on the power extraction performance are systematically investigated. Compared with the traditional flapping foil, it is demonstrated that the enhancement of power extraction efficiency can be achieved with the help of synthetic jets. Based on the numerical analysis, it is indicated that the jet flow on the foil surfaces alters the vortex-shedding process and modifies the pressure distribution on the foil surface. As a result, the overall power extraction of the flapping foil can be benefitted.

Sensitivity study of the wave-driven current in an Arctic frazil-pancake ice zone

A coupled ocean-ice-wave model is used to study ice-edge jet and eddy genesis during surface gravity wave dissipation in a frazil-pancake ice zone. With observational data from the Beaufort Sea, possible wave dissipation processes are evaluated using sensitivity experiments. As wave energy dissipated, energy was transferred into ice floe through radiation stress. Later, energy was in turn transferred into current through ocean-ice interfacial stress. Since most of the wave energy is dissipated at the ice edge, ice-edge jets, which contained strong horizontal shear, appeared both in the ice zone and the ocean. Meanwhile, the wave propagation direction determines the velocity partition in the along-ice-edge and cross-ice-edge directions, which in turn determines the strength of the along-ice-edge jet and cross-ice-edge velocity. The momentum applied in the along-ice-edge (cross-ice-edge) direction increased (decreased) with larger incident angle, which is favorable condition for producing stronger mesoscale eddies, vice versa. The dissipation rate increases (decreases) with larger (smaller) wavenumber, which enhances (reduces) the jet strength and the strength of the mesoscale eddy. The strong along-ice-edge jet may extend to a deep layer (> 200 m). If the water depth is too shallow (e.g., 80 m), the jet may be largely dampened by bottom drag, and no visible mesoscale eddies are found. The results suggest that the bathymetry and incident wavenumber (magnitude and propagation direction) are important for wave-driven current and mesoscale eddy genesis.

Effects of Topography and Realistic Drag on the Southern Hemisphere Midlatitude Jet in a Dry Model

AbstractClimate models have substantial biases in the climatological latitude of the Southern Hemisphere eddy‐driven jet and the time scale of annular mode variability and disagree on the jet response to climate change. Zonally symmetric dry dynamical cores are often used for idealized modeling of the jet response to forcing and its sensitivity to model setup changes. The limits to which these models represent the key mechanisms that control the jet in complex models or the real world have not been systematically investigated. Here we show that substantial intermodel differences in jet latitude and strength can arise from differences in dynamical cores and resolved topography. Including topography and a more realistic surface drag in a dry model substantially alters the jet response to changes in drag strength. Using real‐world maps, enhanced drag over land shifts the jet poleward, whereas enhanced drag over the ocean leads to an equatorward shift. No universal relationship between annular mode time scale and forced response emerges in the dry model with topography. These results suggest that zonally symmetric models with Rayleigh drag lack important mechanisms that control the behavior of the midlatitude jet in coupled climate models. A dry model with topography and quadratic surface drag can fill this gap in the model hierarchy.

Blocking, gap flow and mountain wave interaction along the coastal escarpment of South Africa

A fatal light aircraft crash occurred in the complex mountainous terrain along the coast of the South African Southern Cape in December 2015. An investigation into the meteorological conditions on this day revealed the interaction between mountain waves, gap flow and blocking near a cold front. The crash highlighted the need to equip forecasters with knowledge of the turbulence produced under these circumstances. With this in mind, experiments were conducted in the vicinity of the crash site, with automatic weather stations and radiosondes, to answer this question. Turbulent features were successfully characterised by Froude numbers, the Froude-derived height scale and the thermal wind equation. The Bernoulli equation, which classifies gap flow, was not helpful due to the effect of the upwind blocking area. Phenomena in descending order of wind strength produced compressional effect (44.7 ms−1), blocking (26 ms−1) and lastly, gap flow. Gap flow negatively impacted blocking jet strength. Phenomena in descending order of turbulence intensity gap flow, mountain wave/rotors and lastly, blocking. Gap flow produced greater vertical velocities than mountain waves. These mountain waves produced the highest vertical velocities measured to date in South Africa, associated with the shortest wavelength waves. Blocking jets of 600 m deep, 80 km wide and extending 30 km downwind of its exit region was found to modulate mountain wave characteristics significantly. A combination of mountain waves, gap flow and blocking was most likely responsible for the crash, highlighting that these three features cannot be seen as separate processes.

Active sorting of droplets by using an ECF (Electro-conjugate Fluid) micropump

This paper proposes an on-demand method to sort water-in-oil (W/O) droplets by using an ECF (Electro-Conjugate Fluid) micropump on a chip. ECF is a kind of functional and dielectric oil, which can generate a strong and active flow (called ECF jet) when a high DC voltage is applied to its corresponding anode & cathode in ECF. Targeting at on-demand droplets sorting, we design a new sorter including several parts: a T-junction droplet generator made of SU-8, a sorting area, an ECF micropump, and I/O ports. The ECF combined with a suitable concentration of a surfactant (Span 80) and DI (deionized) water are utilized as the continuous and the dispersed fluids, respectively. The mixture of ECF and Span 80 can also be pumped by our ECF micropump and then forms the ECF jet. The fabrication of the sorter is based on the photolithographic patterning of thick resists (KMPR and SU-8) and the electroforming. We model the ECF micropump and also analyze the sorting performance of our sorter based on the FEM analysis. To validate the sorter, we investigate the influence of two vital parameters of the strength of ECF jets and the droplet sizes on the sorter. Then, we also research the working zones (areas), throughput and sorting efficiency in terms of flow rate ratios and the applied voltages of our device.

Regional and Temporal Variability of Lateral Mixing in the North Atlantic

AbstractGeostrophic eddies contribute to the mixing of heat, carbon, and other climatically important tracers. A passive tracer driven by satellite-derived surface velocity fields is used to study the regional and temporal variability of lateral eddy mixing in the North Atlantic. Using a quasi-Lagrangian diffusivity diagnostic, we show that the upstream region (80°–50°W) of the Gulf Stream jet exhibits a significant mixing barrier (with diffusivity of ≈1 × 103 m2 s−1), compared to the downstream region (50°–10°W), which displays no mixing suppression (≈10 × 103 m2 s−1). The interannual variability is 10%–20% of the time mean in both regions. By analyzing linear perturbations of mixing-length diffusivity expression, we show that the across-jet mixing in the upstream region is driven by variations in the mean flow, rather than eddy velocity. In the downstream region, both the mean flow and eddy velocity contribute to the temporal variability. Our results suggest that an eddy parameterization must take into account the along-jet variation of mixing, and within jets such diffusivities may be a simple function of jet strength.

Study and analysis of the cavitating and non-cavitating jets - Part one: Parameters controlling force, power and the jet behavior

This paper presents the dependency of the jet power and the cavitation intensity on the working conditions of the cavitating and non-cavitating jet flow. This dependency is indicated by the cavitation erosion process and flow structure. The effects of working conditions on the cavitation erosion were experimentally investigated. The flow visualization was done using a high-speed photography recording system. The analysis shows that the erosion rate calculation and the visualization of the jet structure can be used as tools to estimate the jet strength, the jet actions, the jet power, and the performance of the jetting system.

An Overview of Low‐Level Jet Winds and Corresponding Mixed Layer Depths During PECAN

AbstractThirty southerly low‐level jet (LLJ) events were observed during the Plains Elevated Convection at Night (PECAN) field campaign in the Great Plains region of the United States during summer 2015. Here we present Doppler lidar wind data from three PECAN instrumentation sites to explore characteristics of LLJs and the boundary layer as well as some of the heterogeneities possible within the wind field of a LLJ. Southerly LLJs were observed on 66% of nights at the southwestern site (Greensburg, KS) but only 56% and 53% of nights at the eastern and northern sites, respectively (Hesston and Ellis, KS). The northernmost site had a relative abundance of weaker jets or nonjet conditions due to fronts or convective systems that only affected part of the observation domain. Plotting mean wind fields of each LLJ type reveals that the strongest LLJs tend to develop under very similar conditions but begin to show variability in wind profile evolution after several hours. A robust mixed layer height retrieval algorithm is used to investigate the interplay between the jets and the turbulent convective boundary layer, showing that stronger LLJs are preceded by deeper afternoon mixed layers and often have a later decoupling of mixing between the upper convective mixed layer and the near‐surface layer. Only the strongest LLJs generated a shallow mixing layer overnight. Comparing jet strength and direction to pristine nocturnal convection initiation shows that the strongest southerly LLJs yielded the most pristine nocturnal convection initiation events per night, and the pristine nocturnal convection initiation occurred farther north.

Role of premonsoon meridional SST gradient of north Indian Ocean and frequency of typhoon activities on monsoon depression over Bay of Bengal

The paper presents the impact of premonsoon meridional sea surface temperature (SST) gradient of a part of north Indian Ocean (84°E–92°E, 0°N–18°N) and frequency of north-west Pacific weather systems (mainly typhoons and super-typhoons) on the formation of monsoon depressions over Bay of Bengal. Analysis shows that decreasing frequency of monsoon depression over BOB may occur as a result of decreasing trend of premonsoon meridional SST gradients over the region 84°E–92°E and 0°N–18°N. Higher frequency of north-west Pacific weather systems (i.e. higher the total number of typhoons and super-typhoons) during the monsoon month (June, July, August, September-JJAS) may be considered as one of the important aspect for the reduction in monsoon depression frequency over BOB (mostly, during last decade). Tropical easterly jet (TEJ) strength (60°E–100°E, 5°N–20°N) is also analysed to check the relationship between convection over BOB and monsoon circulation pattern which is dependent on SST gradient as well as north-west Pacific weather system frequency. Possible explanation is also presented.

Taylor-Couette flow of shear-thinning fluids

The flow between two concentric cylinders, one of which is rotating (Taylor-Couette flow), has been the focus of extensive research, due to the number of flow instabilities that may occur and its use in various industrial applications. We examine Taylor-Couette flow of Newtonian and shear-thinning fluids (solutions of xanthan gum in water/glycerol) using a combination of particle-image velocimetry and flow visualization for a wide range of Reynolds number, spanning the circular Couette flow, Taylor vortex flow, and wavy vortex flow regimes. Shear thinning is associated with an increase in the axial wavelength and has a nonmonotonic effect on the critical Reynolds number for transition to Taylor vortex flow and wavy vortex flow. The magnitude of vorticity and the strength of the radial jets transporting fluid away from the inner cylinder (“outward jets”) are both reduced in shear-thinning fluids relative to the Newtonian case; the vorticity in the shear-thinning fluids also tends to concentrate at the edges of vortices, rather than in the cores. In the wavy vortex flow regime for Newtonian fluids, the amplitudes of the waves at the “inward jets” (moving toward the inner cylinder) are low compared to those at the outward jets. However, for the shear-thinning fluids, the amplitudes of the waves at both the inward and outward jets tend to be significantly larger. Finally, shear thinning is associated with greater variations in time and space: we observe slow drifts in the axial positions of vortices and spatial variations in the amplitudes of the wavy instability, which are absent in Newtonian fluids.

Role of the position of the North Atlantic jet in the variability and odds of extreme PM10 in Europe

We have analysed the impact of the North Atlantic jet on the winter PM10 (particulate matter with aerodynamic diameter ≤ 10 μm) concentrations in Europe during a 10-year period. For this purpose we have extracted the daily latitude and strength of the jet from a reanalysis dataset and surface PM10 observations from the AirBase network. We show that the detection of the jet over the eastern North Atlantic (0°–15° W) is preferred compared to the whole North Atlantic basin as this maximises the signal on the PM10 concentrations. Four preferred jet positions have been identified over that region and season: southern (south of 41° N), central-southern (between 41° N and 51° N), central-northern (between 51° N and 63° N) and northern (north of 63° N). According to our results, the jet latitude exerts a stronger influence than the jet strength on the mean PM10 levels. We also examine the impact of the jet positions on the full distribution of PM10 as well as on the odds of PM10 extremes (exceedances of the local winter 95th percentiles). The latter is done through a logistic regression model which considers the effect of the persistence of extremes and different time lags for the jet position. The northern position is associated with enhanced PM10 concentrations (on average ∼9 μg m−3) over northwestern/central Europe and threefold increases in the odds of PM10 extremes at most sites in the region. Similar increases have been found for PM10 in southern Europe when the jet is in its central-northern position. In both cases, the rise in the PM10 concentrations is associated with anticyclonic conditions over those regions and the impact on PM10 extremes is maximised for time lags of around 1–2 days. On the other hand, the central-southern and southern jet positions yield large PM10 decreases (on average around −9 μg m−3) in northwestern/central Europe and southern Europe, respectively.

Observed relationship between the Turkana low-level jet and boreal summer convection

The Turkana low-level jet is a circulation feature over northern Kenya that is not spatially well-resolved in many observational datasets. Here, high-resolution TRMM, IMERG, and CMORPH precipitation estimates, along with the ERA5 and MERRA2 reanalyses are analyzed to better understand the controls on jet strength and the relationship between the jet and boreal summer rainfall variability in the jet exit region over South Sudan. The height of the South Sudan wet season, August, is analyzed for 2000–2017. Climatologically, rainfall peaks over the jet exit region during the early morning hours, coinciding with the jet maximum. The strong jet enhances low-level wind convergence and briefly shifts the low-level zonal moisture gradient westward. Over the western South Sudan, rainfall peaks in the late afternoon/evening in association with daytime heating. The correlation between the daily Turkana Jet strength and precipitation indicates a significant negative relationship over eastern South Sudan, and over the Ethiopian and East African Highlands. Composite analysis of strong and weak jet periods reveal that the atmospheric conditions associated with a strong jet include enhanced low-level ridging along the East African coast south of the equator resulting in a stronger height gradient in the Turkana Channel, as well drier conditions over the channel and adjacent highlands. These conditions support a stronger jet that is further enhanced by katabatic flow due to the stronger nighttime cooling over the highlands, as well as enhanced dry air advection over the jet exit region. Thus, while low-level convergence may increase, convection weakens over eastern South Sudan due to the reduced atmospheric moisture content and weaker instability. The opposite occurs for the weak jet case.

Residual layer ozone, mixing, and the nocturnal jet in California's San Joaquin Valley

Abstract. The San Joaquin Valley of California is known for excessive ozone air pollution owing to local production combined with terrain-induced flow patterns that channel air in from the highly populated San Francisco Bay area and stagnate it against the surrounding mountains. During the summer, ozone violations of the National Ambient Air Quality Standards (NAAQS) are notoriously common, with the San Joaquin Valley having an average of 115 violations of the current 70 ppb standard each year between 2012 and 2016. Because regional photochemical production peaks with actinic radiation, most studies focus on the daytime, and consequently the nocturnal chemistry and dynamics that contribute to these summertime high-ozone events are not as well elucidated. Here we investigate the hypothesis that on nights with a strong low-level jet (LLJ), ozone in the residual layer (RL) is more effectively mixed down into the nocturnal boundary layer (NBL) where it is subject to dry deposition to the surface, the rate of which is itself enhanced by the strength of the LLJ, resulting in lower ozone levels the following day. Conversely, nights with a weaker LLJ will sustain RLs that are more decoupled from the surface, retaining more ozone overnight, and thus lead to more fumigation of ozone the following mornings, giving rise to higher ozone concentrations the following afternoon. The relative importance of this effect, however, is strongly dependent on the net chemical overnight loss of Ox (here [Ox] ≡ [O3] + [NO2]), which we show is highly uncertain, without knowing the ultimate chemical fate of the nitrate radical (NO3). We analyze aircraft data from a study sponsored by the California Air Resources Board (CARB) aimed at quantifying the role of RL ozone in the high-ozone events in this area. By formulating nocturnal scalar budgets based on pairs of consecutive flights (the first around midnight and the second just after sunrise the following day), we estimate the rate of vertical mixing between the RL and the NBL and thereby infer eddy diffusion coefficients in the top half of the NBL. The average depth of the NBL observed on the 12 pairs of flights for this study was 210(±50) m. Of the average −1.3 ppb h−1 loss of Ox in the NBL during the overnight hours from midnight to 06:00 PST, −0.2 ppb h−1 was found to be due to horizontal advection, −1.2 ppb h−1 due to dry deposition, −2.7 ppb h−1 to chemical loss via nitrate production, and +2.8 ppb h−1 from mixing into the NBL from the RL. Based on the observed gradients of Ox in the top half of the NBL, these mixing rates yield eddy diffusivity estimates ranging from 1.1 to 3.5 m2 s−1, which are found to inversely correlate with the following afternoon's ozone levels, providing support for our hypothesis. The diffusivity values are approximately an order of magnitude larger than the few others reported in the extant literature for the NBL, which further suggests that the vigorous nature of nocturnal mixing in this region, due to the LLJ, may have an important control on daytime ozone levels. Additionally, we propose that the LLJ is a branch of what is colloquially referred to as the Fresno eddy, which has been previously proposed to recirculate pollutants. However, vertical mixing from the LLJ may counteract this effect, which highlights the importance of studying the LLJ and Fresno eddy as a single interactive system. The synoptic conditions that are associated with strong LLJs are found to contain deeper troughs along the California coastline. The LLJs observed during this study had an average centerline height of 340 m, average speed of 9.9 m s−1 (σ=3.1 m s−1), and a typical peak timing around 23:00 PST. A total of 7 years of 915 MHz radioacoustic sounding system and surface air quality network data show an inverse correlation between the jet strength and ozone the following day, further suggesting that air quality models need to forecast the strength of the LLJ in order to more accurately predict ozone violations.