S. C. Tucker

Aerosol optical and hygroscopic properties during TexAQS‐GoMACCS 2006 and their impact on aerosol direct radiative forcing

[1]xa0In situ measurements of aerosol optical and hygroscopic properties were made on board the National Oceanic and Atmospheric Administration R/V Ronald H. Brown during the Texas Air Quality Study–Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS). The aerosol light extinction coefficient (σep) was measured at 355, 532, and 1064 nm at 25%, 60%, and 85% relative humidity (RH) for both sub-1- and sub-10-μm-diameter particles with a cavity ring–down aerosol extinction spectrometer. The 532-nm σep was coupled with the 532-nm light absorption coefficient (σap) measured with a photoacoustic absorption spectrometer to calculate the aerosol single scattering albedo (ω) with absolute uncertainty 0.65 and >0.9, respectively). The optical data were used to estimate local, top of atmosphere aerosol-induced climate forcing (ΔFR). The ΔFR calculations were performed using both ω values measured at 25% RH and ω values converted to ambient RH. The calculated ambient ΔFR ranged from −7 to −40 W/m2 with absolute uncertainty between 0.7 and 2.5 W/m2. The results show that including aerosol hygroscopic properties in climate calculations is critical for improving estimates of aerosol forcing on climate.

LIDAR-MEASURED WIND PROFILES The Missing Link in the Global Observing System

The three-dimensional global wind field is the most important remaining measurement needed to accurately assess the dynamics of the atmosphere. Wind information in the tropics, high latitudes, and stratosphere is particularly deficient. Furthermore, only a small fraction of the atmosphere is sampled in terms of wind profiles. This limits our ability to optimally specify initial conditions for numerical weather prediction (NWP) models and our understanding of several key climate change issues. Because of its extensive wind measurement heritage (since 1968) and especially the rapid recent technology advances, Doppler lidar has reached a level of maturity required for a space-based mission. The European Space Agency (ESA)s Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) Doppler wind lidar (DWL), now scheduled for launch in 2015, will be a major milestone. This paper reviews the expected impact of DWL measurements on NWP and climate research, measurement concepts, and the recent advances in technology that ...

Turbulent bulk transfer coefficients and ozone deposition velocity in the International Consortium for Atmospheric Research into Transport and Transformation

[1] In this paper, we examine observations of shallow, stable boundary layers in the cool waters of the Gulf of Maine between Cape Cod, Massachusetts, and Nova Scotia, obtained in the 2004 New England Air Quality Study (NEAQS-04), which was part of the International Consortium for Atmospheric Research into Transport and Transformation (ICARTT). The observations described herein were made from the NOAA Research Vessel Ronald H. Brown. The ship was instrumented for measurements of meteorological, gas-phase and aerosol atmospheric chemistry variables. Meteorological instrumentation included a Doppler lidar, a radar wind profiler, rawinsonde equipment, and a surface flux package. In this study, we focus on direct comparisons of the NEAQS-04 flux observations with the COARE bulk flux algorithm to investigate possible coastal influences on air-sea interactions. We found significant suppression of the transfer coefficients for momentum, sensible heat, and latent heat; the suppression was correlated with lighter winds, more stable surface layers, S-SE wind direction, and lower boundary layer heights. Analysis of the details shows the suppression is not a measurement, stability correction, or surface wave effect. The correlation with boundary layer height is consistent with an interpretation that our measurements at 18-m height do not realize the full surface flux in shallow boundary layers. We also find that a bulk Richardson number threshold of 0.1 gives a better estimate of boundary layer height than 0.25 or 0.5. Mean ozone deposition velocity is estimated as 0.44 mm s−1, corresponding to a boundary removal timescale of about 1 day.

Relationships of coastal nocturnal boundary layer winds and turbulence to Houston ozone concentrations during TexAQS 2006

[1]xa0Measurements made with a ship-based Doppler wind lidar during the summertime 2006 Texas Air Quality Study are used to study the relationship between lower-tropospheric vertical structure and winds and ozone (O3) concentrations in Houston, Texas, under two different flow regimes. We observed that strong southerly flow regimes, dominated by the subtropical anticyclone (Bermuda high) off the Atlantic coast of the United States, resulted in strong (i.e., high wind speed) onshore nocturnal low-level jets (LLJ) and low O3 and oxidant Ox (where Ox = O3 + NO2) concentrations at night and the following afternoon. In contrast, periods dominated by northerly or easterly flow resulted in relatively weak (low wind speed), but still onshore, nocturnal LLJs associated with higher concurrent and next-day concentrations of O3 and Ox. We present lidar data from 24 h example periods for each of these conditions and demonstrate how each type of flow regime is related to in situ ship-based ozone measurements. We expanded the study to include all days during the study when the ship was near Houston, to demonstrate how the strength of the meridional winds aloft show a better relationship to concurrent ship-measured Ox concentrations than the winds near the surface do. We found a strong relationship between a parameterization of the observed nocturnal jets, which reflect the synoptic conditions, to peak hourly O3 measured the next day at the ship and averaged throughout the Houston/Galveston/Brazoria continuous ambient monitoring stations monitoring network, indicating potential applications for planning air quality.

Convective venting and surface ozone in Houston during TexAQS 2006

[1]xa0The influence of convective mixing on surface ozone in Houston during TexAQS 2006 is examined. We use airborne lidar measurements of ozone and ship-based Doppler lidar measurements of winds, together with ship- and ground-based measurements of surface ozone to characterize horizontal and vertical mixing of ozone plumes from the Houston Ship Channel on two high-ozone days. We show that a stable capping layer trapped the plume in the boundary layer on 31 August, while shallow convection associated with active fair weather cumulus clouds mixed the plume with free tropospheric air on 17 August. Deep convection associated with an isolated air mass thunderstorm further decreased surface ozone near Galveston Bay in the late afternoon. High ozone thus affected a smaller area for a shorter period on 17 August, despite similar background concentrations and local production. We generalize these findings by comparing Houston ozone concentrations to National Weather Service (Lake Charles, LA) radiosondes. We show that for 1 June to 15 September 2006, stable conditions with high background ozone occurred 18% of the days leading to mean daily 8 h concentrations of 73 ± 11 ppbv. Shallow and deep convection associated with moderate to strongly unstable conditions lowered the mean ozone to 50 ± 11 ppbv (∼29% of days), while weaker convection associated with marginally unstable conditions reduced the mean concentrations to 63 ± 13 ppbv (∼11%). We use these observations to derive simple relationships between surface ozone and convective indicators that may prove useful for parameterization of convective venting in air quality models.

Shipboard multisensor merged wind profiles from the New England Air Quality Study 2004

[1]xa0The New England Air Quality Study (NEAQS) was a regional portion of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) planned by groups in North America and Europe to develop a better understanding of the factors that shape air quality in their respective regions and the remote North Atlantic. The NOAA research vessel Ronald H. Brown was only one of a number of platforms given the task of monitoring the emissions of aerosol and ozone precursors and the atmosphere in which they reside. Two remote and one in situ sensor were used to measure wind profiles. A radar wind profiler (RWP) permanently deployed on the ship and corrected in real time for ship motion provided continuous hourly profiles at 60- and 100-m vertical resolutions. A high-resolution Doppler lidar (HRDL) was also operated during the experiment and provided continuous low-level wind profiles. Rawinsondes were launched 4–6 times daily and provided a detailed profile of winds. Initial results show that the RWP, HRDL, and rawinsonde data compare very well. The ability of HRDL to monitor low-level winds below the minimum range gate of the RWP, while the RWP wind data extend to a much greater height than can be reached by HRDL, make the two systems complementary. Single merged profiles were generated using the RWP and HRDL data, which in turn were used to calculate trajectories to help better understand the transport of pollutants within the Gulf of Maine.

Evolution and new advances in Doppler lidar for atmospheric studies

Doppler lidar continues to advance as a useful method for remote sensing of atmospheric winds. Applications from mobile and ship-based platforms have demonstrated the impact of coherent lidar observations for studying the structure of the stable and marine boundary layers. Airborne deployments enable observations over extended areas, and were used to measure water vapor transport over the US Great Plains. Recently, smaller coherent lidars operating at 1.6 μm have become commercially available. A new direct detection lidar currently will enable airborne observations in aerosol-sparse atmospheric regions. Efforts to extend Doppler lidar to space are underway in Europe, with a Doppler lidar winds mission planned for late 2010.

Development and application of lidar technology for environmental studies

At NOAAs Earth System Research Laboratory, lidar systems have been developed and applied to environmental probing for more than three decades. Progressing from early investigations of atmospheric turbidity and winds employing ruby and CO2 lasers, current work is focused on the application of sensors to measure atmospheric properties important for improving air quality understanding and forecasting, and quantifying important climate forcing mechanisms. Additionally, lidar systems are being used for probing the ocean to observe fish schools and marine mammals for research on estuarine health. Here we briefly describe development and applications of lidar systems for characterizing winds and turbulence in the atmosphere, distribution and transport of ozone and aerosol concentrations in urban areas, and inventory of fish stocks in coastal water.