Satellite-based Nowcasting and Aviation Program

SNAAP Projects

Convectively Induced Turbulence

Decision Support for Avoidance of Convectively Induced Turbulence

This project represents a collaborative effort between UW-CIMSS, NCAR, and UAH to enhance aviation safety by providing better nowcasts and forecasts of convectively-induced turbulence (CIT). Unlike clear-air turbulence forecasts which can be developed to a large extent from NWP model output, CIT forecasts require higher spatial temporal and spatial resolution cloud observations that are only provided by satellite. Specifically we are seeking to identify signatures in GEO and LEO satellite imagery closely associated with convectively-induced turbulence, such as:

1. Overshooting convective tops

2. Convective gravity waves

3. Rapid cirrus anvil expansion, indicative of strong divergence

4. Transverse cirrus outflow bands

5. Newly developing convective storms

A climatology has been developed using experimental Eddy Dissipation Rate (EDR) observations to identify highly turbulent convective events. This EDR data, collected by United Airlines Boeing 757 aircraft, represents an objective measure of the vertical accelerations induced by turbulent atmospheric phenomena. Flight tracks for these EDR-equipped UAL aircraft can be found here, with warm colors representing the highest data density. EDR observations have a distinct advantage over traditional pilot reports (PIREPS) of turbulence, which are subjective and are often reported at a location and time differing from the actual turbulent episode. For highly turbulent events, EDR observations are plotted upon GOES, MODIS, and AVHRR VIS, IR window, and WV imagery to identify cloud-top signatures consistently associated with moderate to severe turbulence. GEO and LEO imagery with EDR turbulence observations for these events can be found in our newly created database.

Of special interest to this effort are turbulent encounters occurring along the edge or outside of a thunderstorm anvil cloud. Because of turbulence hazards in the clear air above and surrounding intense thunderstorm updrafts, FAA flight guidelines suggest that pilots should “avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo.” These guidelines imply that the anvil edge region is relatively “safe” for air traffic. Research from this project suggests that the regions outside the anvil can actually be quite turbulent. Figures 1 and 2 below show cases with a large number of moderate and severe EDR turbulence observations, highlighting the turbulent nature of rapidly expanding anvil clouds and convective gravity waves.

The eventual goal of this effort is to develop satellite-derived interest fields using objective pattern recognition techniques that can be included for testing within the FAA-supported second generation Graphical Turbulence Guidance (GTG2) at NCAR. Improved GTG2 guidance will aid aviation meteorologists, dispatchers, and pilots in making strategic and tactical decisions for avoiding turbulent convection.

Figure 1: GOES-12 4 km IR window imagery on 6/16/2005 showing numerous observations of moderate to severe turbulence associated with a rapidly expanding anvil cloud. Plotted in blue are light, green are moderate, and red are severe EDR turbulence observations. The letter A indicates observations above cloud top, B are below cloud top, C are clear air, and I are at the cloud top. Aircraft observed wind barbs are also shown.

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Figure 2: MODIS 1 km IR window imagery on 7/19/2006 showing turbulence in association with convective gravity waves. Convective gravity waves found during this study have horizontal wavelengths in the 4-6 km range and can only be observed in high-spatial resolution LEO imagery.