A22A-01 INVITED
Chemistry Observations From TC4. First Results
A large suite of both long-lived tracers and reactive gases were measured from the NASA DC8 and WB-57 aircraft during TC4. In addition, several ground-based sites were instrumented. We describe the first results from these investigations designed to both understand the interaction between chemical transport and convection and to evaluate retrievals from various space-borne instruments. In addition, we illustrate several ancillary investigations including sampling of emissions from several active volcanoes and of Amazonian outflow. http://www.espo.nasa.gov/tc4/
A22A-02
Observations of the isotopic composition of vapor and condensed water in the tropical tropopause layer
We present the first simultaneous measurements of the isotopic composition of total water (vapor + condensed) and water vapor in the upper troposphere and lower stratosphere. The isotopic composition of the condensed phase is derived from the difference between the total and vapor phase measurements of the Harvard Hoxotope and ICOS instruments flown on the NASA WB-57 during TC4. These measurements in the tropical tropopause layer (TTL) and in mid-latitudes are used to identify mechanisms for water transport into the TTL and lower stratosphere. Observations within clouds over the Panama Bight region show little difference between the vapor and condensed phase isotope ratios. The uniformity of isotope ratio is consistent with equilibrium thermodynamics and rapid exchange of water with the surrounding airmass. Observations of thin outflow clouds or streamers indicate a higher condensed phase ratio, consistent with transport of water from lower altitudes. Further observations of outflow from deep convection directly into the overworld stratosphere extend the observational database that supports a mechanism for adding water to the stratosphere that bypasses the tropical tropopause.
A22A-03
An Intercomparison of Water Vapor Measurements in the TTL and Lower Tropical Stratosphere during CRAVE and TC4: The Importance and Implications of Laboratory Calibrations With water Vapor Mixing Ratios From 0-10 ppmv.
As part of the effort to validate instruments on the Aura satellite, the Costa Rica Aura Validation Experiment (CRAVE) was flown in January and February of 2006. Systematic differences in measured water vapor in the tropopause region and lower stratosphere between in situ instruments on the WB57, the NOAA Colorado frostpoint hygrometer (CFH) and satellite borne instruments such as the Microwave Limb Sounder (MLS) and the Halogen Occultation Experiment (HALOE) are well-documented. Results from CRAVE, presented during a water vapor workshop organized as part of the CRAVE science meeting, provided further confirmation of these differences. The availability for the first time of multiple robust intercomparisons between these instruments led to the conclusion that at low water mixing ratios (less than 10 ppmv), the differences appear to be well-represented by an offset of about 2 ppmv with in situ instruments on the WB57 measuring higher than MLS and CFH. This enduring discrepancy precludes a satisfactory validation of satellite retrievals of stratospheric water vapor profiles. In this talk we will summarize the recent low water calibration runs in our laboratory that provide direct evidence that the Harvard Lyman alpha instrument measures accurately at low water. We will then compare data taken during the recent TC4 campaign in August 2007 with that from CRAVE and previous campaigns. The implications of the results on our understanding of the mechanisms that control the stratospheric water vapor budget will be discussed.
A22A-04
Water vapor and ozone in the troposphere and stratosphere over Costa Rica and Galapagos during TC4
Intensive observations of water vapor and ozone were taken during the Tropical Composition, Cloud and Climate Coupling (TC4) campaign using balloon borne sensors at San Jose, Costa Rica and at San Cristobal, Galapagos, Ecuador. Water vapor profiles between the surface and the middle stratosphere were measured using Cryogenic Frostpoint Hygrometers (CFH) while ozone profiles were measured using ECC ozone sondes as part of the same payload. Five night time soundings at Costa Rica also carried the Fluorescent Advanced Stratospheric Hygrometer for Balloon (FLASH-B). Ozone profiles indicate that convection over Costa Rica on average reaches about 13 km but ozone remains low compared to Galapagos up to 17.6 km. Water vapor profiles on the other hand show large regional differences up to 14.5 km. Galapagos shows slightly colder tropopause temperatures and slightly higher supersaturation values at the cold point compared to Costa Rica. Dehydration at the cold point appears to be controlled by large scale and stratospheric processes, not by convective processes over Central America. The middle troposphere is significantly drier at Galapagos, although individual layers show relative humidity values larger than those at Costa Rica at similar altitudes. Instrument intercomparisons between FLASH-B and CFH show good agreement in the TTL and cannot explain differences with aircraft sensors which have been previously observed.
A22A-05
Aerosol Composition in the Tropical Troposphere
The PALMS instrument (Particle Analysis by Laser Mass Spectrometry) participated in three Costa Rica aircraft campaigns from 2004 to 2007: Pre-AVE, CR-AVE, and TC4. PALMS measures the chemical composition of individual aerosol particles with diameters >300 nm. Aerosol types were often observed in discrete vertical layers in the troposphere. In some cases, aerosols within the TTL (tropical tropopause layer) showed little resemblance to those in the convective region below or the stratosphere above. TTL aerosol composition was dominated by highly oxidized carbonaceous material. Sulfate was often the principal aerosol component in the convective region. In marine-influenced areas, this sulfate was acidic, whereas sulfate in the TTL was largely neutralized, probably by ammonium. Although all three missions were based from the same site, key features of the aerosol chemistry varied among the missions due to differences in regional convection and sources of air. These variations in aerosol composition may help give insight into mechanisms for air entering the TTL. Additionally, aerosol organic content and the extent of sulfate neutralization have implications for cirrus formation in the TTL.
A22A-06
Convection of Very Short Lived Trace Gases into the TTL, UT and LS.
The Tropical Tropopause Layer (TTL) can be isolated from the free troposphere for days to a month. Measurements of trace gases with similar local lifetimes of days to a month within the upper troposphere (UT), TTL, and lower stratosphere (LS) can identify convective events and reveal information about primary entry points, possible entrainment, and convective outflow. Episodic evidence of convective transport of Very Short Lived Species (VSLS) from the boundary layer to the UT and LS have been seen before. With CH3I for example, evidence for convection occurs primarily if the dominant convective inflow is from a source region within the boundary layer. This episodic data coupled with the host of measurements in missions like Tropical Composition, Cloud, and Climate Coupling experiment (TC4), will continue to improve our understanding of the convective process. At present, a gap exists between this episodic event driven data and an extrapolation to mean distributions and bulk transport. Trace gases like peroxylacytyl nitrate (PAN) have the potential to bridge this gap and may be more suited for integrated zonal comparisons. PAN is unique in two ways. First its lifetime in the TTL is on the order of the upper limit of the residence time of the TTL, and can survive a zonal trip around the globe. The value of PAN measured in the upper troposphere and lower stratosphere therefore contains a statistical distribution from zonal sources, sinks and convection, from within this month timescale. A second difference is that unlike most VSLS species, the source region for PAN extends above the trapped bounder layer. PAN measurements in the UT and TTL are therefore sensitive to convective inflow above the boundary layer in the lower troposphere, as is also the case for water isotope measurements. Most convective processes are highly turbulent with substantial entrainment expected. The dominant convective mass flux into the TTL may not come from the trapped boundary layer where most VSLS are prevalent.
A22A-07
Convective Vertical Redistribution of Trace Gases in the Tropics: A First Look at Chemical Tracer and Meteorological Measurements from the NASA DC-8 during TC4
Fast, accurate in situ chemical tracer and meteorological measurements were made from the NASA DC-8 and from dropsondes during the Tropical Composition, Clouds and Climate Coupling field experiment in the ITCZ region near Costa Rica. These measurements, from the Eastern Pacific and Western Caribbean during summer, show significantly higher mixing ratios of ozone measured throughout the troposphere than do ozone observations from the ITCZ region in the Central Pacific during the PEM Tropics-B field mission during the spring of 1999. Tracer correlations are chaotic when analyzed at 1 second (200 m) resolution, indicating vertical transport and extensive mixing of air by the vigorous convection in this region, and it appears that aged pollution from higher latitudes in the Northern Hemisphere has been well-mixed into the clean Tropical tropospheric background. Given the availability of both hydrocarbons and reactive nitrogen from either this source or from lightning, some of the ozone observed may have been produced in situ, photochemically. Wind and water vapor measurements from sondes launched from the DC-8 provide the means to separate the aircraft data vertically in a dynamically sensitive way. Measurement probability distributions are then used in addition to the tracer correlations and wind measurements to deduce the vertical distribution of primary and ancillary air "types" or source regions in the well-mixed Tropical troposphere. Using these results and a simple mass-balance approach, we estimate the fraction of marine boundary layer air that has been mixed into the upper troposphere, just below the Tropical Transition Layer, and compare to recent mid-latitude estimates from Bertram et. al., (Science, 2007). Finally, we offer some preliminary ideas about why ozone mixing ratios measured near the ITCZ during PEM Tropics-B and TC4 differ so greatly.
A22A-08
Thin cirrus clouds near the tropical tropopause during TC4 and their relation to convection
Cirrus clouds in the tropical tropopause layer (TTL) help govern water mixing ratios at the bottom of the stratosphere and play a role in driving tropical troposphere-to-stratosphere exchange. Though some cirrus clouds are obvious convective anvils, most of the thin cirrus clouds at the tropical tropopause are hundreds of kilometers away from the deep convection that reaches to cirrus altitudes. Nevertheless, a large fraction of the clouds are downstream of convection and are probably caused by the convection in some way. Others are formed "in situ" by cooling along air mass trajectories that is induced by large and mesoscale waves. The recent Tropical Clouds, Chemistry, and Climate Coupling (TC4) experiment conducted in Costa Rica provides extensive observations of these thin cirrus clouds by lidar, some of which are coupled with in situ measurements of cloud and chemical properties. The experiment also included the usual extensive meteorological and standard cloud satellite measurements that allow us to trace the cloud air masses back to convective systems using trajectory analysis. This comprehensive dataset allows us to address some outstanding science questions, including: (1) What fraction of the clouds can be clearly tied to convection, and how does that compare with other regions and seasons?; (2) What is the vertical distribution of the clouds relative to the local temperature structure?; and (3) What tracer signal is seen in the clouds and can that be clearly tied to a convective process?