ACOM

Cloud Tops and Tropopause

The tropopause

The tropopause is a fundamental boundary of the atmosphere, separating the turbulent mixing dominated troposphere from the much more stable and stratified stratosphere. To examine the role of the tropopause and the jet streams in constraining the cloud distributions, ACD scientists performed an analysis of cloud top and tropopause relationships using the Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) cloud data and National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) tropopause data.

Carbon Monoxide Variability over the United States

Surface concentrations of total CO.

Understanding the spatio-temporal distribution of air pollution is made easier if we are able to differentiate between the different processes driving pollutant variations. This involves understanding how the surface and tropospheric concentrations at a given time and location are governed by direct emissions of pollution, chemical processing and transport into the region from further afield.

Chemical Boundary Conditions for Regional Modeling

Plot of lateral boundary conditions in regional atmospheric transport models.

The importance of lateral boundary conditions (BC) in regional atmospheric transport models or numerical prediction models has been well established in the meteorological community. Much more recently, attention has also been drawn to the consideration of chemical lateral boundary conditions in regional chemical transport models (CTMs) and in air quality simulations, and the importance of the inflow of pollution on local air quality.

ENSO and WACCM

Altitude-time composite of anomalies in water vapor.

El Nino-Southern Oscillation (ENSO) is the largest source of interannual variability in the tropical troposphere. Some studies have documented the propagation of the ENSO signal to the stratosphere (Calvo Fernandez et al., 2004; Sassi et al., 2004; Garcia-Herrera et al. 2006) through the anomalous propagation and dissipation of ultralong Rossby waves at middle and high latitudes, which modify the stratospheric mean meridional circulation. A recent study using the Whole Atmosphere Community Climate Model (WACCM3.5), has also shown the intensification of the tropical upwelling in the lowermost part of the stratosphere, below 20km, during warm ENSO events and its weakening during the opposite phase (Calvo et al. 2010). This is mainly due to anomalous forcing by orographic gravity waves especially during the strongest warm ENSO episodes; as a result of anomalies in the location and intensity of the subtropical jets and in the meridional gradient of temperature observed during ENSO episodes.

Cirrus distribution mapped with HIRDLS

Frequency of occurrence (%) of cirrus clouds at 121 hPa.

The vertical depths of cirrus in the upper troposphere vary from less to a kilometer to many kilometers. There is interest in knowing these depths in order to understand how cirrus contributes to the heating and cooling rates in the upper troposphere – a positive solar plus infrared heating rate will impart a positive enhancement to the vertical motion field. Measurements of cirrus by the HIRDLS experiment add to our knowledge base, since the HIRDLS experiment is sensitive to the presence of small amounts of cirrus along limb-views in the upper troposphere.

HOx Observations

Photo of trailers housing the instruments.

HOx image 1aHOx image 1b

Figure 1: Locations of recent measurement campaigns that involved POP group observations. Right-click to view larger images.

Ozone structure of the Upper Troposphere / Lower Stratosphere

Plot of ozone.

The HIRDLS satellite reveals the structure of the Upper Troposphere / Lower Stratosphere (UTLS) region by measuring ozone.

Perturbed Mesospheric Ozone in 2004, 2006, and 2009 NH Winters

SABER observations.

NASA’s SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on the TIMED satellite measures temperature and ozone through the middle atmosphere from 20 to above 100 km. The SABER measurements in NH winter (mid-January through mid-March) capture the evolution of ozone and temperature during recent unusual winters (Figure 1). It is now well documented that the altitude of the temperature maximum (stratopause) was elevated for significant periods in 2004, 2006, and 2009.

MOZART-4: Release, Publication, Forecasts

A WRF-Chem simulation showing high amounts of ozone produced from wildfires.

The global chemical transport model MOZART-4 has been recently released to the scientific community through the ACD MOZART-4 homepage and the NCAR Community Data Portal. The description of MOZART-4 has been submitted to the online journal Geoscientific Model Development [Emmons et al., 2009].

Satellite Observations of Cirrus

Cirrus frequency of occurrence over the western Pacific.

Satellite observations have revealed that cirrus is very prevalent near the tropopause throughout most of the tropics. Cirrus is formed by several processes: a) in-situ rising and freezing of a humid layer, b) blow-off by deep convection, and c) initiation of cirrus formation by the cold temperature perturbations of dynamical waves. The cirrus is of interest since the cirrus restricts the amount of water vapor that is transported from the upper troposphere into the lower stratosphere.

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ACOM | Atmospheric Chemistry Observations & Modeling