World Wind Regimes - Caspian Sea Mountain Wave Tutorial

	NRL Monterey, Marine Meteorology Division http://www.nrlmry.navy.mil

World Wind Regimes - Caspian Sea Mountain Wave Tutorial

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Background

Fig. 1. Streamlines in the Steady Airflow over an Isolated Asymmetric Ridge with a Steep Leeward Slope

Note in this model depiction how streamlines indicate a strong downdraft at lower levels in the lee of the mountain, while a violent updraft forces wave cloud formation at higher levels.

Examples

Fig. 2.	Fig. 3.

Fig. 2 shows the topography of the Caspian Sea region. Most notable is the Caucasus Mountain range that stretches WNW to SSE across Southern Russia the position of Mt. El'Brus, the highest elevation in Europe (18,481 ft). The terrain falls off from this peak to less than 5000 ft in only 25 miles to the northeast. The build-up to this elevation from the southwest from sea level, however, occurs in over 60 nm. It is apparent that this range conforms to the "gentle windward slope/steep leeward slope" configuration that that could lead to mountain wave production. The range is also perfectly aligned to intercept strong southwest winds from an approaching upper level trough in a fashion to produce such waves.

Fig. 2.

Fig. 3.

Fig. 2 shows the topography of the Caspian Sea region. Most notable is the Caucasus Mountain range that stretches WNW to SSE across Southern Russia the position of Mt. El'Brus, the highest elevation in Europe (18,481 ft). The terrain falls off from this peak to less than 5000 ft in only 25 miles to the northeast. The build-up to this elevation from the southwest from sea level, however, occurs in over 60 nm. It is apparent that this range conforms to the "gentle windward slope/steep leeward slope" configuration that that could lead to mountain wave production. The range is also perfectly aligned to intercept strong southwest winds from an approaching upper level trough in a fashion to produce such waves.

Fig 4. METEOSAT-7 Infrared Image, 2 Nov 2001, 2200Z (Surface Winds Superimposed)	Fig. 5. METEOSAT-7 Infrared Image. 2 Nov 2001, 2200Z (500 mb Pattern Superimposed)	Fig. 6. METEOSAT-7 Infrared Image. 2 Nov 2001, 2200Z (300 mb Winds Superimposed)

Fig. 4 reveals a classically formed vertically propagating mountain wave cloud suggesting the approach of an upper level trough. The cloud appears to have formed downstream of the crest of the mountain range. Surface winds are quite light through the region, so it is obvious that the forcing factor for wave formation is the existence of stronger winds aloft. Note also thin wisps of cirrus, suggesting flow from the southwest. Fig. 5 reveals the approaching 500 mb trough that has produced the ideal conditions for vertically propagating mountain wave production. Fig. 6 shows the 300 mb wind barbs, indicating strong wind flow of over 50 knots at this level. Any plane flying in the leeward region of the mountain range at lower levels where this cloud pattern exists would be likely to experience severe downdraft conditions. Many unwary aircraft have been forced into mountain sides because of this condition. Note: Because of the treacherous mountain terrain over Afghanistan, Navy meteorologists should be especially on the alert for the development of similar conditions in that region. REFERENCES Durran, D. R., 1986: Mountain Waves. Mesoscale Meteorology and Forecasting,P. S. Ray (ed.) Amer. Meteor. Soc., Boston, MA.

Fig 4. METEOSAT-7 Infrared Image, 2 Nov 2001, 2200Z (Surface Winds Superimposed)

Fig. 5. METEOSAT-7 Infrared Image. 2 Nov 2001, 2200Z (500 mb Pattern Superimposed)

Fig. 6. METEOSAT-7 Infrared Image. 2 Nov 2001, 2200Z (300 mb Winds Superimposed)

Fig. 4 reveals a classically formed vertically propagating mountain wave cloud suggesting the approach of an upper level trough. The cloud appears to have formed downstream of the crest of the mountain range. Surface winds are quite light through the region, so it is obvious that the forcing factor for wave formation is the existence of stronger winds aloft. Note also thin wisps of cirrus, suggesting flow from the southwest.

Fig. 5 reveals the approaching 500 mb trough that has produced the ideal conditions for vertically propagating mountain wave production.

Fig. 6 shows the 300 mb wind barbs, indicating strong wind flow of over 50 knots at this level. Any plane flying in the leeward region of the mountain range at lower levels where this cloud pattern exists would be likely to experience severe downdraft conditions. Many unwary aircraft have been forced into mountain sides because of this condition.

Note: Because of the treacherous mountain terrain over Afghanistan, Navy meteorologists should be especially on the alert for the development of similar conditions in that region.

REFERENCES

Durran, D. R., 1986: Mountain Waves. Mesoscale Meteorology and Forecasting,P. S. Ray (ed.) Amer. Meteor. Soc., Boston, MA.

Author: Bob Fett
Last Updated: Mon Dec 9 10:49:36 2002
Produced by: The Composer (Ver: 1.1.2 )

NRL Monterey, Marine Meteorology Division http://www.nrlmry.navy.mil