Climatology of Upper-Level Turbulence over the Contiguous United States

Abstract

Climatologies of the regional, seasonal, and temporal distributions of upper-level (18 000-60 000-ft MSL) turbulence over the contiguous United States (CONUS) are constructed using pilot reports (PIREPs) of aircraft turbulence encounters. The PIREP database used contains over two million entries, and encompasses 12 complete years of data, from January 1994 through December 2005. In spite of known variability in pilot reporting practices, it was found that PIREPs are very consistent among themselves for the null and moderate-or-greater (MOG) intensity categories. Air traffic pattern biases were accounted for by considering only statistics of MOG/total report ratios. Over the CONUS, regional maxima are evident in MOG/ total ratios over mountainous regions in the west, over the south and southeast, and over the North Atlantic seaboard. Some additional investigations are presented to help to identify possible origins of the turbulence using a smaller time interval of PIREPs in comparison with archived 20-km Rapid Update Cycle (RUC) NWP model analyses, satellite and radar-based cloud-top and cloud-base analyses, and lightning flash data, as well as topography statistics.

Climatology of Velocity and Temperature Turbulence Statistics Determined from Rawinsonde and ACARS/AMDAR Data

“…There is a pronounced maximum over the Rocky Mountains (see Fig. 14), consistent with previous results (Nastrom and Gage 1985;Jasperson et al 1990;Jaeger and Sprenger 2007;Wolff and Sharman 2008). The maximum off the southeast coast of the United States was also found in Wolff and Sharman (2008).…”

“…The minimum of the turbulence levels at an altitude of 8 km (400 hPa) for the 408-508N latitude band reflects the lower turbulence region below the jet stream and above the convective boundary layer. This climatology of smaller-scale turbulence may provide useful connections to scales of turbulence that impact aviation safety (Wolff and Sharman 2008).…”

“…Last, note that, as more and more aircraft become AMDAR equipped, it may be feasible to compute structure functions locally in real time and thus infer locations of elevated turbulence levels and provide new tools for turbulence detection and aviation safety (Wolff and Sharman 2008). by NASA ROSES Grant NNX08AL89G.…”

“…There is little difference in the temperature statistics at larger scales, but the smaller scales have substantially lower levels over Eurasia than over CONUS. The levels of D LL and D NN also have higher levels over CONUS than over Eurasia at the smaller scales, probably due to enhanced mountain wave activity over the Rocky Mountains in winter and to thunderstorm activity over the eastern half of the United States in summer (Wolff and Sharman 2008), compared to Eurasia. At larger scales D NN has the zonal wavenumber 7 peak mentioned in section 4c, and dominates D LL over both regions.…”

“…Other three-dimensional estimates of turbulence climatology have been attempted by Jaeger and Sprenger (2007) using 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data and by Wolff and Sharman (2008) using pilot reports (PIREPS) of turbulence. However, both of these techniques are somewhat unreliable given the uncertainty in turbulence diagnostic formulations and model data used in the former and the subjective nature of PIREPs in the latter.…”