C. S. Eubank

Reactive nitrogen and its correlation with ozone in the lower stratosphere and upper troposphere

Reactive nitrogen (NOy) and O3 were measured simultaneously from a NASA ER-2 aircraft during 1987 through 1989. These high resolution measurements cover a broad range of latitudes in the upper troposphere and lower stratosphere. The data show a striking positive correlation between NOy and O3 in the lower stratosphere at all scales sampled. The ratio NOy/O3 is nearly independent of altitude from the tropopause to above 20 km, with ratios in the stratosphere of 0.0015–0.002 in the tropics and 0.0025–0.004 elsewhere. The ratio is much more constant than either individual species, thus providing an excellent reference point for comparing limited data sets with models. Two-dimensional models reproduce general features of the vertical profile of NOy/O3 but not the gradient in the lower stratosphere between tropics and mid-latitudes. NOy and O3 are better correlated in the lower stratosphere than in the upper troposphere. The magnitude and variability of both NOy mixing ratios and NOy/O3 ratios indicate a source of NOy in the upper troposphere. The most plausible source in the tropics is lightning production of NOx. Condensation of NOy onto aerosol particles is often possible in the tropical upper troposphere and may play a role in determining the vertical distribution of NOy. In the mid-latitude upper troposphere the data suggest long-range transport of NOy. NOy mixing ratios in the tropical upper troposphere were usually between 150 and 600 pptv, enough so that upward transport can affect the NOy abundance in the tropical lower stratosphere.

Retrieval of effective radius and liquid water path from ground-based instruments : A case study at Barrow, Alaska

best for moderately thick clouds (LWP � 100 g m � 2 ), but the accuracy is limited by uncertainties in the MWR LWP on which it relies. The second method performed well over a wider range of values with 1s retrieval errors of <4 g m � 2 (� 4%) and � 3 mm (� 7%) for 15 � LWP � 170 g m � 2 . The LWPs retrieved using the radiance-PLWP method were highly correlated (r 2 = 0.96) with LWPs from the MWR (with a bias subtracted) derived using the ARM statistical method. A limited comparison (LWP < 100 g m � 2 ) to millimeter wave cloud radar showed that values of re retrieved using the radiance-PLWP method were consistently higher (by � 3 mm) than the LWC-weighted mean re from the radar. Additional field studies are needed to resolve this discrepancy, although this first comparison is promising.

Airborne observations of vegetation and implications for biogenic emission characterization.

Measuring hydrocarbons from aircraft represents one way to infer biogenic emissions at the surface. The focus of this paper is to show that complementary remote sensing information can be provided by optical measurements of a vegetation index, which is readily measured with high temporal coverage using reflectance data. We examine the similarities between the vegetation index and in situ measurements of the chemicals isoprene, methacrolein, and alpha-pinene to estimate whether the temporal behavior of the in situ measurements of these chemicals could be better understood by the addition of the vegetation index. Data were compared for flights conducted around Houston in August and September 2000. The three independent sets of chemical measurements examined correspond reasonably well with the vegetation index curves for the majority of flight days. While low values of the vegetation index always correspond to low values of the in situ chemical measurements, high values of the index correspond to both high and low values of the chemical measurements. In this sense it represents an upper limit when compared with in situ data (assuming the calibration constant is adequately chosen). This result suggests that while the vegetation index cannot represent a purely predictive quantity for the in situ measurements, it represents a complementary measurement that can be useful in understanding comparisons of various in situ observations, particularly when these observations occur with relatively low temporal frequency. In situ isoprene measurements and the vegetation index were also compared to an isoprene emission inventory to provide additional insight on broad issues relating to the use of vegetation indices in emission database development.