7The Soil Moisture and Ocean Salinity (SMOS) remote sensing satellite was launched by the European Space Agency in 2009. The L-band brightness temperature observed by SMOS has been used to produce estimates of both soil moisture and τ , the optical thickness of the land surface. Although τ should theoretically be proportional to the amount of vegetation present within a SMOS pixel, several initial investigations have not been able to confirm this expected behavior. However, when the noise in the SMOS τ product is removed, τ in the U.S. Corn Belt, a region of extensive row-crop agriculture, has a distinct shape that mirrors the growth and development of crops. We find that the peak value of SMOS τ occurs at approximately 1000 • C day (base 10 • C) growing degree days after the mean planting date of maize (corn). We can explain this finding in the following way:τ is directly proportional to the water column density of vegetation; maize contributes the most to growing season changes in τ in the Corn Belt; and maize reaches its maximum water column density at its third reproductive stage of development, at about 1000 • C day growing degree days.Consequently, SMOS τ could be used to monitor the phenology of crops in the Corn Belt at a spatial resolution similar to a U.S. county and a temporal frequency on the order of days. We also examined the magnitude of the change in SMOS τ over the growing season and hypothesized it would be related to the amount of accumulated solar radiation, but found this not to be the case.On the other hand, the change in magnitude was smallest for the year in which the most precipitation fell. These findings are rational since SMOS τ at the satellite scale is in fact a function of both vegetation and soil surface roughness, and soil surface roughness is reduced by precipitation.To fully explain changes in SMOS τ in the Corn Belt it appears that it will be necessary to use in situ and remotely-sensed observations along with agro-ecosystem models to account for land management decisions made by farmers that affect changes in soil surface roughness and all of the relevant biophysical processes that affect the growth and development of crops.

13This paper presents airborne measurements of multiple atmospheric trace constituents including 14 greenhouse gases (such as CO 2 , CH 4 , O 3 ) and biomass burning tracers (such as CO, CH 3 CN) downwind of an 15 exceptionally large wildfire. In summer 2013, the Rim wildfire, ignited just west of the Yosemite National 16 Park, California, and burned over 250,000 acres of the forest during the 2-month period (17 August to 24 17 October) before it was extinguished. The Rim wildfire plume was intercepted by flights carried out by the 18 NASA Ames Alpha Jet Atmospheric eXperiment (AJAX) on 29 August and the NASA DC-8, as part of 19 SEAC 4 RS (Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional 20 Surveys), on 26 and 27 August during its intense, primary burning period. AJAX revisited the wildfire on 10 21September when the conditions were increasingly smoldering, with slower growth. The more extensive 22 payload of the DC-8 helped to bridge key measurements that were not available as part of AJAX (e. g. CO). 23Data analyses are presented in terms of emission ratios (ER), emission factors (EF) and combustion 24 efficiency and are compared with previous wildfire studies. ERs were 8.0 ppb CH 4 (ppm CO 2 ) -1 on 26 25 August, 6.5 ppb CH 4 (ppm CO 2 ) -1 on 29 August and 18.3 ppb CH 4 (ppm CO 2 ) -1 on 10 September 2013. The 26 increase in CH 4 ER from 6.5-8.0 ppb CH 4 (ppm CO 2 ) -1 during the primary burning period to 18.3 ppb CH 4 27 (ppm CO 2 ) -1 during the fire's slower growth period likely indicates enhanced CH 4 emissions from increased 28 smoldering combustion relative to flaming combustion. Given the magnitude of the Rim wildfire, the 29 impacts it had on regional air quality and the limited sampling of wildfire emissions in the western United 30

No abstract

Abstract. Stratosphere-to-troposphere transport (STT) results in air masses of stratospheric origin intruding into the free troposphere. Once in the free troposphere, ozone (O 3 )-rich stratospheric air can be transported and mixed with tropospheric air masses, contributing to the tropospheric O 3 budget. Evidence of STT can be identified based on the differences in the trace gas composition of the two regions. Because O 3 is present in such large quantities in the stratosphere compared to the troposphere, it is frequently used as a tracer for STT events.This work reports on airborne in situ measurements of O 3 and other trace gases during two STT events observed over California, USA. The first, on 14 May 2012, was associated with a cutoff low, and the second, on 5 June 2012, occurred during a post-trough, building ridge event. In each STT event, airborne measurements identified high O 3 within the stratospheric intrusion, which were observed as low as 3 km above sea level. During both events the stratospheric air mass was characterized by elevated O 3 mixing ratios and reduced carbon dioxide (CO 2 ) and water vapor. The reproducible observation of reduced CO 2 within the stratospheric air mass supports the use of non-conventional tracers as an additional method for detecting STT. A detailed meteorological analysis of each STT event is presented, and observations are interpreted with the Realtime Air Quality Modeling System (RAQMS). The implications of the two STT events are discussed in terms of the impact on the total tropospheric O 3 budget and the impact on air quality and policy-making.