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Many people have a turbulence story: perhaps a specific memorable experience or just an unpleasant flight where the seatbelt sign remained on for hours. While more rare, severe turbulence encounters can result in serious (even fatal) injuries and significant operational costs to airlines. While storms themselves are highly turbulent, they can also modify their environment in ways that lead to turbulence far from the storm. Using limited datasets, past studies indicate moderate or greater (MoG) turbulence can extend beyond current federal guidelines for avoidance (20 mi or 32 km), but many questions remain. For example, 1) What is the spatial distribution of turbulence relative to storms? 2) What environmental factors influence the spatial distribution? Now, extensive archives of radar data and automated turbulence reports from commercial aircraft allow us to thoroughly investigate turbulence near storms. To this end, we compare turbulence reports to storm locations over 9 years (2009–17) in the United States. We find that 32 km from 10-dBZ echoes at flight altitude, the risk of MoG turbulence is nearly 5 times the background occurrence and that elevated risk extends beyond 100 km. At 2 km above echo tops, the risk of MoG turbulence exceeds 20 times the background risk. This decreases exponentially but remains elevated at all vertical separation distances. Risks increase with storm intensity. Finally, when we use ERA5 reanalysis to assess environmental factors, we find increased risk with stronger mean wind and wind shear, with slightly higher risk downstream and to the left of the wind/shear vector. SIGNIFICANCE STATEMENT: When airplanes experience turbulence, it can be unpleasant and even dangerous for passengers and crew. It can also damage aircraft. Therefore, people involved in determining where airplanes fly (e.g., pilots and air traffic control) generally avoid turbulence, but this can be challenging and expensive for airlines. Thunderstorms cause turbulence, and an airplane seemingly far away may still feel its effects. Since the 1960s, when federal guidelines about avoiding thunderstorms first came out, observations of both storms and turbulence have improved. However, details (like distance) of risk near thunderstorms have not been studied with these better data until now. We found that at 70 km away from where weather radar identifies storms at aircraft heights, the risk of turbulence is twice as high as usual and that risk is always high above storms. We also found that the risk of turbulence is higher when storms are more intense and that the position of the airplane is relative to features like environmental wind and the tropopause impact risk. [ABSTRACT FROM AUTHOR]

The one‐third power of the energy dissipation rate (EDR), a primary aviation turbulence metric, is calculated using high vertical‐resolution radiosonde data (HVRRD) and compared with flight‐EDR observed from commercial airlines. Comparisons are made along the main flight routes over the United States and at z = 20–45 kft for 6 years (2012–2017). The horizontal distributions of moderate‐or‐greater (MOG) ratio of HVRRD‐EDR show large values over the Rocky Mountains, consistent with those of flight‐EDR. Vertically, the MOG ratios of HVRRD‐EDR show local peaks at z = 20–23 kft and 41–44 kft, while those of flight‐EDR at z = 23–26 kft and 35–41 kft. Temporally, HVRRD‐EDR has maximum MOG values in JJA and minimum values in DJF at z = 20–30 kft, which is opposite to the flight‐EDR. At z = 30–40 kft, HVRRD‐EDR shows nearly no seasonal variation but flight‐EDR has large values in MAM and small values in JJA. At z = 40–45 kft, HVRRD‐EDR (flight‐EDR) shows large values in MAM and small values in SON (DJF). Discrepancies in spatiotemporal distributions between the two data sets likely stem from: (a) turbulence observed from the two data sets cannot be the same event, (b) the limitation of HVRRD‐EDR in capturing shear‐instability under statically stable condition (i.e., Kelvin‐Helmholtz instability) which probably accounts for most flight‐EDR events at upper levels, and (c) limitation in aircraft measurements response to fluctuations at smaller scales than the aircraft size. Plain Language Summary: We calculated a primary aviation turbulence metric, eddy dissipation rate (EDR), using operational high‐resolution radiosonde data and compared it with flight‐EDR observed from commercial airlines. EDR is an index for representing the intensity of turbulence. Analyzing 6 years of data (2012–2017) over the United States, we find that the horizontal distributions of both EDRs from radiosonde data and flight data show large values over the Rocky Mountains. However, they show large differences in vertical and temporal distributions in terms of their peak location and timing. We attribute these discrepancies to three factors. First, turbulence observed from the two data sets cannot be the same event, because the radiosonde and aircraft cannot coincide at the same location and time. Second, the sources of turbulence derived from radiosonde and flight observation may be different: static‐instability and dynamic‐instability for radiosonde‐EDR and flight‐EDR, respectively. Third, aircraft have limitations detecting fluctuation at scales smaller than the aircraft size. Given the limited global data on atmospheric turbulence, EDR estimated from operational radiosonde data can be a valuable resource for research and development for the aviation industry and numerical weather forecasting models. Key Points: Radiosonde‐derived turbulence is applied to aviation turbulence metricSpatiotemporal distributions of radiosonde‐ and flight‐turbulence are comparedCauses of discrepancies between radiosonde‐ and flight‐turbulence are discussed [ABSTRACT FROM AUTHOR]

Spatial and temporal distributions of Clear‐Air Turbulence (CAT) in the Northern Hemisphere were investigated using 41 years (1979–2019) of the European Centre for Medium‐range Weather Forecast Reanalysis version 5 (ERA5) data. We used two groups of CAT diagnostics to determine occurrence frequencies: (a) commonly used empirical turbulence indices (TI1, TI2, and TI3) and their components [vertical wind shear (VWS), deformation, ‐divergence, and divergence tendency], and (b) theoretical instability indicators [Richardson number (Ri), potential vorticity (PV), and Brunt‐Vӓisӓlӓ frequency]. The empirical indices showed high frequencies of moderate‐or‐greater (MOG)‐level CAT potential over the East Asian, Eastern Pacific, and Northwestern Atlantic regions in winter. Over East Asia, the entrance region of strong upper‐level jets showed the highest frequencies in TI1, TI2, and TI3 due mainly to strong VWS. The Eastern Pacific and Northwestern Atlantic areas near the exit region of jets had relatively high frequencies of these indices and also Ri. PV frequency was high on the southern side of jet primarily due to negative relative vorticity. Long‐term increasing trends of MOG‐level CAT potential also appeared in those three regions mainly due to warming in lower latitudes. The most significant increasing trend was found over East Asia, due to the strengthening of the East Asian jet and increased VWS due to the strong meridional temperature gradients in the mid‐troposphere induced by warming in the tropics and cooling in eastern Eurasia. These trends over East Asia, if continued, are expected to be of importance to efficient aviation operations across the northwestern Pacific Ocean. Plain Language Summary: Strong bumpiness of cruising aircraft can lead to physical injuries for crews and passengers, which is mostly occurred due to atmospheric turbulence by enhanced wind shear near upper‐level jet stream. Spatial characteristics of turbulence and their long‐term trends at cruising altitude in Northern Hemisphere were examined using the up‐to‐date global reanalysis data. The result showed that East Asia, Eastern Pacific, and Northwestern Atlantic regions have a higher frequency of turbulence than other areas. In particular, East Asia was found to be the highest frequency and the largest increasing trend of strong turbulence, which is collocated with a heavy air‐traffic region between East Asia and North America across the North Pacific Ocean. This implies that the potential of encountering turbulence over East Asia could be increased further, if the jet stream will be strengthened continually due to climate change in this region. Key Points: Spatial and temporal distributions of Clear‐Air Turbulence (CAT) indices for 41 years in the Northern Hemisphere are derived using the highest resolution of reanalysis dataThe CAT potentials are high in three regions: the East Asian, Eastern Pacific, and Northwestern Atlantic regions due to upper‐level jetsIncreasing trend of CAT potentials is the largest in East Asia due to warming in tropics and cooling over the Eurasian continent, which have a high impact on transpacific flights [ABSTRACT FROM AUTHOR]

Area-averaged estimates of [C.sup.2.sub.n] from high-resolution numerical weather prediction (NWP) model output are produced from local estimates of the spatial structure functions of refractive index with corrections for the inherent smoothing and filtering effects of the underlying NWP model. The key assumptions are the existence of a universal statistical description of small-scale turbulence and a locally universal spatial filter for the NWP model variables. Under these assumptions, spatial structure functions of the NWP model variables can be related to the structure functions of the atmospheric variables and extended to the smaller underresolved scales. The shape of the universal spatial filter is determined by comparisons of model structure functions with the climatological spatial structure function determined from an archive of aircraft data collected in the upper troposphere and lower stratosphere. This method of computing [C.sup.2.sub.n] has an important advantage over more traditional methods that are based on vertical differences because the structure function--based estimates avoid reference to the turbulence outer length scale. To evaluate the technique, NWP model--derived structure-function estimates of [C.sup.2.sub.n] are compared with nighttime profiles of (7,2 derived from temperature structure-function sensors attached to a rawinsonde (thermosonde) near Holloman Air Force Base in the United States. DOI: 10.1175/2010JAMC2350.1

The characteristics and dynamics of inertia-gravity waves generated in the vicinity of an intense jet stream/ upper-level frontal system on 18 February 2001 are investigated using observations from the NOAA Gulfstream-IV research aircraft and numerical simulations. Aircraft dropsonde observations and numerical simulations elucidate the detailed mesoscale structure of this system, including its associated inertia-gravity waves and clear-air turbulence. Results from a multiply nested numerical model show inertia-gravity wave development above the developing jet/front system. These inertia-gravity waves propagate through the highly sheared flow above the jet stream, perturb the background wind shear and stability, and create hands of reduced and increased Richardson numbers. These bands of reduced Richardson numbers are regions of likely Kelvin-Helmholtz instability and a possible source of the clear-air turbulence that was observed.

An investigation of the generation of turbulence above deep convection is presented. This investigation is motivated by an encounter between a commercial passenger aircraft and severe turbulence above a developing thunderstorm near Dickinson, North Dakota, on 10 July 1997. Very high-resolution two- and three-dimensional numerical simulations are used to investigate the possible causes of the turbulence encounter. These simulations explicitly resolve the convection and the turbulence-causing instabilities. The configurations of the models are consistent with the meteorological conditions surrounding the event. The turbulence generated in the numerical simulations can be placed into two general categories. The first category includes turbulence that remains local to the cloud top, and the second category includes turbulence that propagates away from the convection and owes its existence to the breakdown of convectively generated gravity waves. In both the two- and three-dimensional calculations, the local turbulence develops rapidly and occupies a layer about 1 km deep above the top of convective updrafts after their initial overshoot into the stratosphere. This local turbulence is generated by the highly nonlinear interactions between the overshooting convective updrafts and the tropopause. Gravity wave breakdown is only present in the two-dimensional calculation and occurs in a layer about 3 km deep and 30 km long. This gravity wave breakdown is attributed to an interaction between the gravity waves and a critical level induced by the background wind shear and cloud-induced wind perturbations above cloud top.