Reverse Ray Tracing Research Articles

Focus on Software

Focus on Software

Gravity waves and mesospheric clouds in the summer middle atmosphere: A comparison of lidar measurements and ray modeling of gravity waves over Sondrestrom, Greenland

We conducted gravity wave ray‐tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67°N, 310°E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three‐dimensional daily‐varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi‐vertically from 40–80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally‐inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real‐time runs with the model in 2001 using weather forecast data as a low‐level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.

Case Studies of Gravity Waves Associated with Isolated Tornadic Storms on 13 January 1976

Penetrative convection, thunderstorms, squall lines, etc., all generate atmospheric gravity waves which can be observed by a ground-based ionospheric Doppler sounder array. Sources of these waves can be determined from reverse ray tracing computations. Case studies of gravity waves associated with isolated tornadic storms on 13 January 1976 were summarized to establish the minimum data sampling time required for correct spectral analysis and ray tracing computations. It was concluded that the data sampling time can be reduced to two to three times the wave period while still obtaining a reasonably good power spectral density. It was also demonstrated that the data sampling time can be reduced to two to three times the time delay of the wave arrival between two station pairs while still obtaining a justifiably good cross-spectral analysis. Computed source locations of the observed gravity waves are compared with conventional and satellite meteorological data.

Dynamics of severe storms through the study of thermospheric-tropospheric coupling.

Atmospheric acoustic-gravity waves associated with severe local thunderstorms, tornadoes, and hurricanes can be studied through the coupling between the thermosphere and the troposphere. Reverse group ray tracing computations of acoustic-gravity waves, observed by an ionospheric Doppler sounder array, show that the wave sources are in the neighborhood of storm systems and the waves are excited prior to the storms. It is suggested that the overshooting and ensuing collapse of convective turrets may be responsible for generating the acoustic-gravity waves observed. The results of this study also show that the study of wave-wave resonant interactions may be a potential tool for investigating the dynamical behavior of severe storm systems using ionospheric observations of atmospheric acoustic-gravity waves associated with severe storms.

The meteorological jet stream as a source of medium scale gravity waves in the thermosphere: an experimental study

Results are reported of a co-ordinated experimental study of medium scale gravity waves involving use of a multistatic incoherent scatter system together with two networks of polarimeters monitoring transmissions from a geostationary satellite during a six-day period in July 1974. The latter observations give access to the horizontal propagation parameters of the waves while the former technique yields information on the vertical structure of both waves and the ambient atmosphere. A reverse ray tracing analysis, through the atmosphere, for each gravity wave is described and its validity and accuracy discussed in detail. For the majority of the waves the reverse group path can be followed down to tropopause level and comparison with meteorological data has shown that many of the possible source regions of the observed waves appear to lie in proximity to the jet stream, with some evidence to suggest a preference for the polar side of the jet. Other wave sources are found to be close to regions of convectively unstable cold polar air. Wave energetics are discussed together with possible generation mechanisms, the latter in the form of non-linear interaction of shear flow instabilities in the jet stream and penetrative convection.

Observation of gravity waves during the extreme tornado outbreak of 3 April 1974

Gravity waves or medium scale TID's with wave periods of 13–15 min and 27–30 min and with horizontal phase velocities of 90–217 m/s were observed at F-region ionospheric height during the time period (1700–2200 UT) of the extreme tornado outbreak of 3 April 1974. Large scale TID's with wave periods of 36 min and a horizontal phase velocity 350 m/s were also detected at 2200–2400 UT, the same day. A group ray tracing technique, using data on the neutral atmosphere and neutral wind profiles (30 to 100 km altitude from meteorological rocketsonde data and above 100 km altitude from a theoretical wind model), has been used in an attempt to locate the sources of these waves. A comparison of the computed sources of the waves (medium scale TID's) and the actual locations and times of tornado touchdowns has resulted in the classification of the tornadoes into several groups. In this study the signals (medium scale TID's) were observed 1–3 h ahead of the touchdowns of the tornadoes. The result from the reverse ray tracing of the large scale TID's showed that the wave sources were located in the aurora zone and at auroral latitude in which Kp index was 6 at the time of wave excitation. The summation of 24 hours Kp index for this day was 36. The result agrees with existing theories of large scale TID's associated with geomagnetic activity at autora zone.

Medium scale gravity waves in the ionospheric F-region and their possible origin in weather disturbances

This study results from a coordinated experiment involving ionospheric observations of Faraday rotation between a geostationary satellite and three ground based receivers at Aberystwyth and Bournemouth in the U.K. and Lannion, France, together with incoherent scatter observations at St. Santin-Nancay, France. Quasi-periodic variations of electron content observed simultaneously at the three stations are interpreted in terms of medium scale gravity waves travelling in the ionospheric F-region. Characteristics of these waves are derived by means of a cross-correlation technique. A reverse ray tracing computation, using data on the neutral atmosphere and neutral wind stratification from the incoherent scatter observations, has been used in an attempt to locate the sources of these waves. The results show that some of the waves are almost certainly generated above 100 km altitude, probably by auroral phenomena, while the others could be produced near ground level by meteorological sources. The reverse ray tracing indicates that the latter sources are in general located in a geographic area in the vicinity of a weather disturbance. A production mechanism for these waves is proposed involving ageostrophic perturbations of the neutral wind in a jet stream.