Ozone measurements from Atlantic Tropical Cyclones Thomas P

Ozone measurements from Atlantic Tropical Cyclones Thomas P. Carsey, Hugh Willoughby Thomas. P. Carsey@noaa. gov, Hugh. Willoughby@noaa. gov NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, Atlantic Oceanographic and Meteorological Laboratory, 4301 Rickenbacker Causeway, Miami, Florida 33149 ABSTRACT INSTRUMENTATION AND DATA HANDLING Tropical cyclones (TCs, hurricanes) are episodic mesoscale features of the tropical and subtropical oceans that are likely to have a large impact on the distributions and fluxes of trace gases. The troposphere boundary layer, possibly enriched by enhanced exchange of dissolved gases from the sea surface, can be transported upward as high as 15 km and redistributed over a large horizontal area. Measurements of selected trace gases should therefore be useful in understanding hurricane dynamics and structure; for example, to clarify an ongoing controversy about the lifetime of air within the eye and mixing areas of the eye wall boundary (Willoughby, Mon. Wea. Rev. 126, 3053, 1998). However, few systematic measurements of significant trace gases in TCs have been obtained. NOAA-AOML has measured ozone (O 3) in eyewall crossings for a number of Atlantic TCs during the 1998 and 1999 seasons on board NOAA P-3 hurricane research flights. We have found unusual changes in ozone concentration indicative of the strength and age of the particular hurricane. Table I: HURRICANES INVESTIGATED IN THIS STUDY Deployment: on P-3 N 43 RF during the 1998 and 1999 hurricane seasons. Instrument: Environics Models 300 B Ozone Analyzer (UV absorption). Pressure correction using ambient (exterior) pressure applied; no temp correction employed (assumed cabin temperature). Air lines of Teflon® (0. 635 cm [¼ inch]-OD) connected instrument inlet and outlet to exterior of aircraft. Calibration: at Dade County Department of Environmental Resources Management (DERM) in Miami, using EPA protocol, prior to each field season, and was found to be accurate to <2%; with a precision of <1% rsd at 100 ppb. Data handling: Instrument output (voltages) collected by aircraft’s data collection system, along with time, position, radar altitude, ambient pressure, air temperature, dew point, relative humidity, liquid water, and wind speed, at ten-second intervals. Eye passes were identified by wind speed and temperature extremes, and checked with aircraft results (www. aoml. noaa. gov/hrd). A correction (70 sec) was applied to account for instrument response time, as determined in laboratory testing. Relative ozone change was computed using ozone concentration near but outside the eye region as 100%; a change in ozone concentration during the eye transect was expressed as a percentage of that baseline concentration. No. of Eye Pass Times Location Pass Alt Invers Lyr MSLP 1 MWS 2 Name Date Passes (local) Lon Lat (km) ht (h. Pa) Time(GMT) (kts) Notes Bonnie Danielle Georges Mitch Bret Dennis Floyd Irene 23 -Aug-98 24 -Aug-98 26 -Aug-98 29 -Aug-98 19 -Sept-98 28 -Sept-98 27 -Oct-98 20 -Aug-99 26 -Aug-99 27 -Aug-99 29 -Aug-99 13 -Sept-99 14 -Sept-99 15 -Sept-99 14 -Oct-99 19: 48 -20: 20 15: 52 -20: 24 11: 59 -17: 33 15: 42 -20: 51 14: 20 -15: 24 5: 57 -11: 25 15: 32 -18: 25 14: 50 -17: 05 13: 10 15: 31 -20: 24 14: 49 -19: 42 14: 42 -19: 21 14: 42 -15: 29 15: 58 -22: 42 15: 54 -21: 20 71. 7ºW 24. 8ºN 85. 6ºW 16. 6ºN 77. 8ºW 33. 7ºN 71. 2ºW 25. 8ºN 54. 0ºW 15. 5ºN 88. 9ºW 30. 4ºN 85. 6ºW 16. 6ºN 94. 5ºW 21. 6ºN 73. 9ºW 24. 6ºN 76. 1ºW 26. 1ºN 78. 1ºW 31. 7ºN 74. 7ºW 24. 3ºN 77. 2ºW 26. 5ºN 78. 5ºW 32. 0ºN 82. 6ºW 23. 1ºN 5 1. 5 2. 1 (2. 4) 5 4. 5 1. 6 -1. 9 3 (5. 3) 5. 1 3. 6 4. 2 4. 3 3. 2 2 2. 1 1. 5 707 855 850 890 filled weak 975 846 755 849 filled 850 filled 954 24 -Aug 0000 100 highly assym. , second eyewall Landfall 27 -Aug 3: 30 z 954 3 -Sep 0600 100 weak; followed Bonnie 937 20 -Sep 0600 135 just prior to max intens. landfall 11: 30 z 28 -Sep 905 26 -Sept 155 prior to landfall 944 22 -Aug 1200 100 assym. , poorly formed 962 30 -Aug 0600 90 eye not well organized very irregular O 3 msmts just prior to max intens. 921 13 -Sep 1200 135 cat 4 storm eyewall replc; landfall eyewall replc 956 18 -Oct 0756 95 north of Cuba 1: MSLP (minimum sea level pressure) and WS (maximum wind speed) from www. nhc. noaa. gov Illustration of the secondary (non-rotational) flow in the eye and eyewall of a hurricane. The frictional indraft feeds the buoyancy-driven primary updraft and outflow in the eyewall cloud. Inflow under the eyewall is derived from convective downdrafts It, and evaporatively driven descent along the inner edge of the eyewall, feed moist air into the volume below the inversion. Gradual descent of dry air inside the eyewall warms the air column adiabatically. The descent is forced as convection draws mass from the bottom of the eye into the eyewall. Balance between moist-air production and loss to the eyewall determines the rate of rise or fall of the inversion. The nature of the eye of a tropical cyclone has been the subject of recent investigation (Kossin and Eastin, 2001; Kossin et al. , 2000; Dodge et al. , 1999; Willoughby, 1998; Emanuel 1997). These studies have clarified the structural changes which occur in the life of a storm: in an intensifying storm, the air in the eye above a descending inversion layer is warmer and dryer than the surrounding air; in a weakening storm the air becomes cooler and wetter, and the inversion layer ascends. The transition between the two modes may be completed very rapidly (Kossin and Eastin, 2001). Track of Hurricane Floyd. Minumum surface pressure (923 h. Pa) indicated. Source: R. Pasch, T. Kimberlain, and S. Stewart, Preliminary Report on Hurricane Floyd, National Hurricane Center, 1999 Floyd originated in western Africa on 2 September 1999, became a hurricane on the 10 th, and attained maximum strength on the 13 th; msw (maximum surface winds) increased from 95 to 135 knots, and the central pressure fell ~40 mb from the 12 th to the 13 th. Floyd became a category 4 by 13 September, possibly due to unusually warm sea surface temperatures, but subsequently diminished in strength. Floyd passed over Eleuthera (Bahamas) on 15 September, and made landfall near Cape Fear, NC on 16 September as a category 2 storm. Floyd was losing its eye wall Radar reflectivity data: 22: 56 structure as it made landfall. Floyd became a tropical storm on the 16 th 23: 01 z, 13 sep and disappeared on into the north Atlantic on the 19 th. triangle: position of max wind speed, 22: 36 z. Aircraft was traveling southwestward. at 1800 z Floyd had a mslp of 923 h. Pa and msw of 125 kts (Pasch et al. , 1999), Figure 1 A. The eye was warmer and dryer than the surrounding air; the highest wind speeds are obtained just outside the eyewall (64 m s-1 northeast of the eye). The eye, 40 km in diameter, is narrowing and an eye wall replacement is beginning. The ozone profile reveals very low Radar reflectivity ozone in the eye wall, nearly 20% below the surrounding (vicinal) ozone data: 20: 29 z, concentration of ~16. 4 ppb. The eye shows asymmetry, with stronger 15 sep triangle: position of max convection towards the north and east. wind speed, 20: 29 z. Aircraft was traveling westward. The next day (FIgure 1 B), the storm as weakened only slightly at the time of sampling (20: 29 z), with a mslp of 930 mb and msw of 110 kts (Pasch, op. cit. ). An eye wall replacement had occurred. The eye is much less warm than the previous day, and is much more moist, and the low-ozone MBL air previously confined to the eye wall has now filled the eye. Dropsondes no Radar reflectivity longer show the presence of an inversion layer. data: 23: 27 -23: 34 z, 16 sep triangle: The storm crossed land at 06: 30 on the 16 th, near Cape Fear, NC as a category 2 storm. Aircraft sampling a few hours before (01: 09 z) is shown in position of max wind speed, 23: 40 z. Figure 1 C. Surface winds have decreased, the eye is drier and warmer. Aircraft was Ozone concentration was significantly decreased (up to 10%) compared to traveling westward. the surrounding areas. Dropsonde results showed the reemergence of an inversion layer, at about 820 h. Pa, at the time of the sampling. 2 5 5 6 3 5 6 4 1 5 4 4 2 6 5 Eye air chemistry: Floyd, 7 -17 Sep. , 1999 Floyd was sampled for ozone from 13 through 16 September. On the 13 th Hurricane eye structure (Willoughby 1988) FIGURE 1 A LW: liquid water; T: air temperature, DP: dew point; WS: true wind speed; %Ozone: ozone concentration as percent of extra-eye ozone concentration at the same altitude. Eyewall replacment has begun. Aircraft altitude ~3 km across eye. Inversion layer at ~0. 8 km. FIGURE 1 B Units as above. Note that moist, ozone-poor air has filled and cooled the eye. Aircraft altitude was ~4 km. Eyewall replacement continues. Inversion layer has disappeared. FIGURE 1 C Units as above. Aircraft altitude ~2 km. Storm has weakened. An inversion layer at ~0. 9 km has reformed. Ozone in rain bands OZONE AND RELATIVE HUMIDITY Rain bands due to convection are dominant features of the hurricane surrounding the eye. It is expected that the uplifted air, rich in ozone-poor boundary layer air, would have decreased ozone concentration. Thus, decreased ozone concentration is an indicator for convection comparable to radar reflectivity. Increased ozone, relative to that of the extra-storm region, would indicate the presence of stratospheric air. (RESULTS AND DISCUSSION ABOUT THE RELATIONSHIP OF OZONE AND DEW POINT, POINTING OUT THEIR OPPOSITE SOURCES (OZONE FROM ABOVE, HUMIDITY FROM THE SEA SURFACE). The presence of ozone in rain bands was observed in most of the data sets. Examples are shown below. Figure 2 A. Hurricane Dennis, 27 -Aug-99, 22: 04 z. The storm will reach maximum intensity on 30 -Aug. Horizontal axis approximately describes aircraft flight path through the eyewall. Relative ozone concentration is elevated in the eye due to descending air, and is depressed in the eyewall. Elevated ozone also depressed in the rain band at ~26. 8 o. N and 25. 4 o. N. The radar reflectivity image has a somewhat different time base than the ozone measurements made as the aircraft passed through the eye. Track of hurricane Dennis, 24 -Aug through 4 -Sept, 1999. Source: J. Bevin, Preliminary report on Hurricane Dennis, NHC, 2000. SUMMARY AND CONCLUSIONS (draft) 1) Ozone undergoes dramatic changes in the eye region of hurricanes, which approxiamately follow dew point but are do differ on occasions. 2) Generally, is elevated in the eyewall prior to intensification and depressed following intensification, following humidity, but may be higher. This may indicate the presence of continental air as apposed to marine boundary layer air, as the source air. Figure 2 B. Hurricane Bonnie, 24 -Aug-98, 23: 20 z. The hurricane was barely past peak intensity (24 -Aug, 0000 z, 954 mb). This intense storm was highly asymmetric at this time. The eye, which had elevated ozone the day before, is now dominated by low-ozone boundary layer air. Rain bands can be seen at 27. 7 o. N and 27. 9 o. N. Between the rain bands, residual air with elevated ozone is sampled. The horizontal axis approximately defines the aircraft track. The hurricane track is shown at right. Track of hurricane Bonnie, 19 -30 August, 1998. Source: L. Avila, Preliminary report on Hurricane Bonnie, NHC, 1998. 3) Ozone measurements may thus aid in the determination of the peak intensity, and thus the development of the eye. These changes may be incorporated into hurricane models to as an additional constraint. 4) … 1. ACKNOWLEDGEMENTS 2. The authors would like to thank the NOAA Aircraft Operations Center for their valued assistance with obtaining measurements on the aircraft, an on scientist and staff of the NOAA/AOML’s hurricane research division for help with the data processing and plotting.