Slide 1

Airborne Studies of Atmospheric Dynamics Thomas R. Parish Department of Atmospheric Science University of Wyoming Slide 2 Newtons Second Law The Equation of Motion Total Derivative Local Derivative Advection (Inertia) Term Horizontal Pressure Gradient Force Gradient Force Coriolis Force GeostrophiccomponentAgeostrophiccomponent Slide 3 Geostrophic Wind Balanced flow state Balanced flow state Purely rotational (non-divergent) Purely rotational (non-divergent) Often the largest component of wind Often the largest component of wind Relatively inert component of the wind Relatively inert component of the wind LH Vg PC Slide 4 Ageostrophic Wind Unbalanced flow state Unbalanced flow state Often contains significant divergent component Often contains significant divergent component Generally small component of wind Generally small component of wind Isallobaric and inertia/advective components generally largest Isallobaric and inertia/advective components generally largest Important forcing component of the wind Important forcing component of the wind Slide 5 Measurement of Geostrophic Wind Write Equation of Motion in isobaric coordinates Variation of height on a pressure surface proportional to horizontal pressure gradient force Variation of height on a pressure surface proportional to horizontal pressure gradient force Airborne applications use autopilot Airborne applications use autopilot Slide 6 Pre-GPS Era (before 2004) Radar Altimeter measurements provide height above surface Radar Altimeter measurements provide height above surface Terrain maps (digital) provide terrain height assuming geographic position known with high accuracy Terrain maps (digital) provide terrain height assuming geographic position known with high accuracy Height of isobaric surface is sum of above signals Height of isobaric surface is sum of above signals Slide 7 Problems: Two signals (radar altimeter heights, terrain height) large and of opposite sign Two signals (radar altimeter heights, terrain height) large and of opposite sign PGF is the sum of those terms, being quite small and noisy PGF is the sum of those terms, being quite small and noisy Potential errors in both radar altimeter height, terrain height Potential errors in both radar altimeter height, terrain height Artifact problem for radar altimeter Artifact problem for radar altimeter Footprint issue for altimeter Footprint issue for altimeter Uncertainties in aircraft position estimates Uncertainties in aircraft position estimates Issues with terrain height data sets Issues with terrain height data sets Resulting uncertainty with terrain registration Resulting uncertainty with terrain registration Slide 8 Example: Great Plains Low-Level Jet Nocturnal summertime jet maximum ~400 m agl Nocturnal summertime jet maximum ~400 m agl Competing theories for LLJ formation Competing theories for LLJ formation Blackadar frictional decoupling Blackadar frictional decoupling Holton sloping terrain influence Holton sloping terrain influence Slide 9 Slide 10 Slide 11 Slide 12 Flight Strategy Repeating isobaric legs Results of PGF measurements at lowest level Slide 13 Conclusions: Isallobaric component of wind ~4 m/s at level maximum wind Isallobaric component of wind ~4 m/s at level maximum wind Large changes in turbulent intensity at jet level Large changes in turbulent intensity at jet level Blackadar frictional decoupling dominant mechanism in Blackadar frictional decoupling dominant mechanism in forcing Great Plains LLJ forcing Great Plains LLJ Slide 14 GPS Era Avoid terrain registration issues Avoid terrain registration issues GPS provides a means to accurately map isobaric surface GPS provides a means to accurately map isobaric surface Position errors from standard GPS receiver insufficient to Position errors from standard GPS receiver insufficient to resolve isobaric slopes Differential GPS required Differential GPS required Requires fixed base station Requires fixed base station Position errors at base station can be used to correct Position errors at base station can be used to correct position errors for rover platform (aircraft) position errors for rover platform (aircraft) Importance of acceptable satellite constellation (5 or 6?) Importance of acceptable satellite constellation (5 or 6?) Position accuracy on order of decimeters Position accuracy on order of decimeters Relative accuracy probably much better Relative accuracy probably much better Slide 15 GPS04 Study Arcata CA Frequent summertime LLJ at top of marine boundary layer Frequent summertime LLJ at top of marine boundary layer Comparison with altimetry-derived geostrophic wind Comparison with altimetry-derived geostrophic wind Tested GrafNav differential processing software Tested GrafNav differential processing software Slide 16 GPS04 LLJ Example Isobaric east-west flight leg south of Cape Mendocino Isobaric east-west flight leg south of Cape Mendocino Nearly identical signals Nearly identical signals dGPS calculations of Vg from most legs within 1 m/s altimetry Vg dGPS calculations of Vg from most legs within 1 m/s altimetry Vg GPS04 validated dGPS technique GPS04 validated dGPS technique Slide 17 Slide 18 Application of dGPS on atmospheric dynamics Coastally Trapped Wind Reversals (CTWRs, also CTDs, southerly surges) 0000 UTC 22 June - 0000 UTC 26 June 2006 Slide 19 CTWR Forcing Issues Kelvin Wave Kelvin Wave Cross-coast PGF Cross-coast PGF Variations in MBL Height Variations in MBL Height Topographic Rossby Wave Topographic Rossby Wave Topographically-Trapped Wave Topographically-Trapped Wave Density Current Density Current Synoptic-scale response Synoptic-scale response Ageostrophic acceleration Ageostrophic acceleration Importance of synoptic-scale pressure field Importance of synoptic-scale pressure field Slide 20 23 June 2006 Example Isobaric east-west Isobaric east-west flight leg flight leg Little detectable Little detectable cross-coast PGF cross-coast PGF Slide 21 23 June 2006 Example Slide 22 Slide 23 Slide 24 24 June 2006 Example Slide 25 Slide 26 23-25 June 2006 CTWR Conclusions CTWR density current CTWR density current No Kelvin-wave features observed during this event No Kelvin-wave features observed during this event Active propagation phase highly ageostrophic Active propagation phase highly ageostrophic Little detectable cross-coast PGF at any time during the life history Little detectable cross-coast PGF at any time during the life history Onset and propagation dependent on synoptic pressure field Onset and propagation dependent on synoptic pressure field Slide 27 Application: CloudGPS08 May-June 2008, flights over high plains WY, NE, CO May-June 2008, flights over high plains WY, NE, CO Measure horizontal perturbation pressures associated with clouds Measure horizontal perturbation pressures associated with clouds Clouds mostly in cumulus congestus phase Clouds mostly in cumulus congestus phase Differential GPS dependent on accurate measurement of static pressure Differential GPS dependent on accurate measurement of static pressure Slide 28 Application: CloudGPS08 (May 21) Slide 29 Liquid Water Content (g/kg) Isobaric Height W (m/s) uvuv Horizontal Pressure Perturbation (mb) VV Slide 30 Liquid Water Content (g/kg) W (m/s) Horizontal Pressure Perturbation (mb) Slide 31 Application: CloudGPS08 (June 17) Slide 32 Leg 1 Liquid Water Content (g/kg) W (m/s) Horizontal Pressure Perturbation (mb) uvuv VV Isobaric Height Slide 33 Leg 2 Liquid Water Content (g/kg) W (m/s) Horizontal Pressure Perturbation (mb) uvuv VV Isobaric Height Slide 34 Leg 3 Liquid Water Content (g/kg) W (m/s) Horizontal Pressure Perturbation (mb) uvuv VV Isobaric Height Slide 35 Leg 4 Liquid Water Content (g/kg) W (m/s) Horizontal Pressure Perturbation (mb) uvuv VV Isobaric Height Slide 36 Leg 5 Liquid Water Content (g/kg) W (m/s) Horizontal Pressure Perturbation (mb) uvuv VV Isobaric Height Slide 37 Leg 1 Slide 38 Leg 2 Slide 39 Leg 3 Slide 40 Leg 4 Slide 41 Leg 5 Slide 42 Application: Ocean Surface Topography Differences between GPS height, radar altimeter signal measure of ocean surface topography Differences between GPS height, radar altimeter signal measure of ocean surface topography Slide 43 Application: Ocean Surface Topography Reciprocal legs along 40.8N Reciprocal legs along 40.8N Consistent pattern of height Consistent pattern of heightdifferences Validate using multiple altimeters? Validate using multiple altimeters? Gulf Stream flights? Gulf Stream flights? Slide 44 Application: Ocean Surface Topography Reciprocal legs along 40.8N Reciprocal legs along 40.8N Consistent pattern of height Consistent pattern of heightdifferences Validate using multiple altimeters? Validate using multiple altimeters? Gulf Stream flights? Gulf Stream flights? Slide 45 Application: Ocean Surface Topography Slide 46 Conclusions dGPS can provide precise mapping of aircraft height dGPS can provide precise mapping of aircraft height Base station data rate 1 Hz Base station data rate 1 Hz Baseline ~ 100 km? Baseline ~ 100 km? dGPS accuracy within decimeters? dGPS accuracy within decimeters? Relative accuracy higher? Relative accuracy higher? Accurate measurement of static pressure permits PGF calculations Accurate measurement of static pressure permits PGF calculations Assessment of atmospheric dynamics for a wide variety of flows Assessment of atmospheric dynamics for a wide variety of flows Thanks to Dave Leon, Larry Oolman, Dave Rahn and Eric Parish