Evaporation Duct Profile Comparisons Using Kites and Bulk Methods LT Deborah L. Mabey March 20, 2001

Acknowledgements Professor Davidson Professor Guest Paul Frederickson everyone on Leg II, especially Jennifer Hauser

Pictures                                            

Purpose Calculate M directly using a rawinsonde suspended from a kite Calculate M profiles using bulk methods from ship’s sensors kite data Compare profiles and associated duct heights Determine the effect of any differences on radar (using AREPS for visualization)

Background vertical gradient of M (modified refractivity) determines how far the horizon is dM/dz < 0 greatly increases distance to the horizon M = f( p, T, e ) dM/dz < 0 near the surface due to strong negative vapor pressure gradient caused by evaporation (hence the name evaporation duct)

Evaporation Duct 15 10 5 Z0 Z (m) M 80 90 100 RH (%)

More background M can be calculated directly: M profiles can be obtained using bulk methods (which require T, p, e, u, z and an iterative method to determine the scaling parameters) See Air/Sea Interaction (MR/OC 4413) & EMEO (MR 4416) course notes for painful details

Effects of Ducts ) (Hz x 10 Significantly affected by duct MHZ 6 10 4 (Hz x 10 Significantly affected by duct 10 3 MHZ 10 2 Not Significantly affected by duct Frequency in 10 0 200/60 400/120 600/180 800/240 1000/300 Duct Thickness (ft/m)

Measurements Rawinsonde suspended from kite time, height, pressure, air temperature, relative humidity, dew point temperature (recorded every 2 seconds while kite was flying) R/V Point Sur’s SAIL system time, pressure, air temperature, relative humidity, port true wind speed, boom temperature (recorded every 52 to 56 seconds) NPS Meteorology Department instruments time, pressure, air temperature, relative humidity, true wind speed, infrared detected sea surface temperature (recorded every 5 seconds and integrated over 2 minute intervals) Hand-held infrared sensor sea surface temperature (recorded hourly)

Problems Flying a kite with a rawinsonde attached is not as easy as it sounds Surface pressure was not constant while the kite was being flown NPS Meteorology Department IR sea surface temperature sensor did not work while in San Francisco Bay

SST and pressure problems

Solutions (assumptions) Although the kite was flown on three separate occasions, only the last flight is presented (assuming that skill of flying kite away from ship increased with practice) Negative heights (due to varying pressure) corrected by assuming minimum rawinsonde height was always 1 meter Hand-held infrared sea surface temperatures were substituted for unreliable NPS infrared detected sea surface temperatures for use in bulk profiles

Analysis calculated M for each data point for three (2 up, 1 down) kite profiles (blue x’s) averaged M at each z level (blue o’s) and used a best-fit cubic (blue line) calculated bulk M profile using ship’s data (red line) calculated bulk M profile using NPS data (with hand-held IR SST) (green line) Calculated bulk M profiles using kite data at approximately ¼ (cyan line), ½ (magenta line) and ¾ (black line) of the maximum height of the kite (with hand-held IR SST and NPS wind speed)

Results All graphs shown are for experiment 17 but are representative of all results shown in the table

Pressure

Temperature

Relative Humidity

Modified Refractivity

Evaporation Duct Height (meters) Experiment 17 (up) 141 data points 18 (down) 261 data points 19 (up) Kite 14.4 16.9 13.1 SAIL 6.7 6.2 5.9 NPS 6.4 6.8 ¼ 7.6 7.3 ½ 7.1 7.0 ¾ 7.5

AREPS GENERIC Radar

Any Questions? ?