DRUM Community: Atmospheric & Oceanic Science

TROPOSPHERIC OZONE AND ITS RADIATIVE EFFECTS DUE TO ANTHROPOGENIC AND LIGHTNING EMISSIONS: GLOBAL AND REGIONAL MODELING

2012-01-01T00:00:00Z

Title: TROPOSPHERIC OZONE AND ITS RADIATIVE EFFECTS DUE TO ANTHROPOGENIC AND LIGHTNING EMISSIONS: GLOBAL AND REGIONAL MODELING Authors: Martini, Matus Abstract: We analyze the contribution of North American (NA) lightning and anthropogenic emissions to summertime ozone concentrations, radiative forcing, and exports from North America using the global University of Maryland chemistry transport model (UMD-CTM) and the regional scale Weather Research and Forecasting model with chemistry (WRF-Chem). Lightning NO contributes by 15–20 ppbv to upper tropospheric ozone concentrations over the United States with the effects of NA lightning on ozone seen as far east as North Africa and Europe. Using the UMD-CTM, we compare changes in surface and column ozone amounts due to the NOx State Implementation Plan (SIP) Call with the natural variability in ozone due to changes in meteorology and lightning. Comparing early summer 2004 with 2002, surface ozone decreased by up to 5 ppbv due to the NO_x SIP Call while changes in meteorology and lightning resulted in a 0.3–1.4 ppbv increase in surface ozone. Ozone column variability was driven primarily by changes in lightning NO emissions, especially over the North Atlantic. As part of our WRF-Chem analysis, we modify the radiation schemes to use model-calculated ozone (interactive ozone) instead of climatological ozone profiles and conduct multiple 4-day simulations of July 2007. We found that interactive ozone increased the outgoing longwave radiation (OLR) by 3 W m−2 decreasing the bias with respect to remotely sensed OLR. The improvement is due to a high bias in the climatological ozone profiles. The interactive ozone had a small impact on mean upper troposphere temperature (−0.15°C). The UMD-CTM simulations indicate that NA anthropogenic emissions are responsible for more ozone export but less ozone radiative forcing than lightning NO emissions. Over the North Atlantic, NA anthropogenic emissions contributed 0.15–0.30 W m−2 to the net downward radiative flux at the tropopause while NA lightning contributed 0.30–0.50 W m−2. The ozone export from anthropogenic emissions was almost twice as large as that from lightning emissions. The WRF-Chem simulations show that the export of reactive nitrogen was 23%–28% of the boundary layer emissions and 26%–38% of the total emissions including lightning NO.

FIELD OBSERVATIONS AND MODEL SIMULATIONS OF LOW-LEVEL FLOWS OVER THE MID-ATLANTIC DURING AUGUST 1-5, 2006

2012-01-01T00:00:00Z

Title: FIELD OBSERVATIONS AND MODEL SIMULATIONS OF LOW-LEVEL FLOWS OVER THE MID-ATLANTIC DURING AUGUST 1-5, 2006 Authors: Rabenhorst, Scott Daniel Abstract: For years, basic mountain, sea breeze, and low-level jet (LLJ) circulations have been studied, usually in locations with a high frequency of occurrence, sharp gradients, or significant geographic prominence. However, there is evidence that similar circulations exist in non-classic locations with more mild topography and atmospheric gradients. One such understudied area is the U.S. Mid-Atlantic region. The Water Vapor Variability - Satellite/Sondes (WAVES) 2006 field campaign provided a contiguous 5-day period of concentrated high resolution observations to examine fine-scale details of a weather pattern typical of the Mid-Atlantic summertime. These measurements presented an opportunity for an intensive modeling study to further investigate peculiar phenomena with verification against research-grade observations. The observations captured two significant events: an official LLJ and a cold front with a prefrontal trough. A pronounced diurnal cycle was revealed which can be categorized into three stages: (1) daytime growth of the planetary boundary layer (PBL), (2) flow intensification into a LLJ regime after dusk, and (3) interruption by downslope winds (DW) after midnight. The third stage is most interesting owing to the lack of literature documenting similar occurrences in the Mid-Atlantic, which can impact air quality forecasting. Prior to high resolution modeling of the case study, sensitivity studies were conducted examining four areas to which the model was believed most sensitive: (1) initial condition data, (2) cumulus schemes, (3) PBL parameterizations, and (4) initialization times. Results also revealed shortcomings in model precipitation and PBL profiles, model biases, urban anomalies, and tendencies for forecast convergence. High resolution regional modeling showed the evolution of these nocturnal events and were verified against WAVES observations. A hybrid solenoidal influenced afternoon and early evening circulation east of the mountains. Afternoon deepening of a lee trough by an oscillating warm air band influenced low-level wind fields. Wind flow was further influenced by the thermal wind that originated over sloping terrain. Airflow traversed the Appalachian barrier and moved down the east flank of the Appalachians with katabatic and hydraulic contributions. This DW swept the LLJ regime off to the southeast. The prefrontal LLJ outflow in the Midwest strengthened DW events as the cold front approached.

A STUDY OF REMOTELY SENSED AEROSOL PROPERTIES FROM GROUND-BASED SUN AND SKY SCANNING RADIOMETERS

2012-01-01T00:00:00Z

Title: A STUDY OF REMOTELY SENSED AEROSOL PROPERTIES FROM GROUND-BASED SUN AND SKY SCANNING RADIOMETERS Authors: Giles, David Matthew Abstract: Aerosol particles impact human health by degrading air quality and affect climate by heating or cooling the atmosphere. The Indo-Gangetic Plain (IGP) of Northern India, one of the most populous regions in the world, produces and is impacted by a variety of aerosols including pollution, smoke, dust, and mixtures of them. The NASA Aerosol Robotic Network (AERONET) mesoscale distribution of Sun and sky-pointing instruments in India was established to measure aerosol characteristics at sites across the IGP and around Kanpur, India, a large urban and industrial center in the IGP, during the 2008 pre-monsoon (April-June). This study focused on detecting spatial and temporal variability of aerosols, validating satellite retrievals, and classifying the dominant aerosol mixing states and origins. The Kanpur region typically experiences high aerosol loading due to pollution and smoke during the winter and high aerosol loading due to the addition of dust to the pollution and smoke mixture during the pre-monsoon. Aerosol emissions in Kanpur likely contribute up to 20% of the aerosol loading during the pre-monsoon over the IGP. Aerosol absorption also increases significantly downwind of Kanpur indicating the possibility of the black carbon emissions from aerosol sources such as coal-fired power plants and brick kilns. Aerosol retrievals from satellite show a high bias when compared to the mesoscale distributed instruments around Kanpur during the pre-monsoon with few high quality retrievals due to imperfect aerosol type and land surface characteristic assumptions. Aerosol type classification using the aerosol absorption, size, and shape properties can identify dominant aerosol mixing states of absorbing dust and black carbon particles. Using 19 long-term AERONET sites near various aerosol source regions (Dust, Mixed, Urban/Industrial, and Biomass Burning), aerosol absorption property statistics are expanded upon and show significant differences when compared to previous work. The sensitivity of absorption properties is evaluated and quantified with respect to aerosol retrieval uncertainty. Using clustering analysis, aerosol absorption and size relationships provide a simple method to classify aerosol mixing states and origins and potentially improve aerosol retrievals from ground-based and satellite-based instrumentation.

ON THE RAPID INTENSIFICATION OF HURRICANE WILMA (2005)

2012-01-01T00:00:00Z

Title: ON THE RAPID INTENSIFICATION OF HURRICANE WILMA (2005) Authors: Chen, Hua Abstract: Previous studies have focused mostly on the roles of environmental factors in the rapid intensification (RI) of tropical cyclones (TCs) due to the lack of high-resolution data in the inner-core regions. In this study, we examine the RI issue by analyzing 72-h cloud-permitting model predictions of Hurricane Wilma (2005) with the Weather and Research Forecast (WRF) model at the finest grid sizes of 1-2 km. The 72-h predictions cover Hurricane Wilma¡¦s initial 18-h spin up, an 18-h RI and the subsequent 36-h weakening stage. The model prediction uses the initial and lateral boundary conditions, including a bogus vortex, that are identical to the Geophysical Fluid Dynamics Laboratory's then-operational data, except for the time-independent sea surface temperature (SST) field. The model predicts an RI rate of more than 4 hPa h-1 for an 18-h period, with the minimum central pressure of less than 889 hPa. It was found that an upper-level warm core forms in the same layer as the upper outflow, in coincidence with the onset of RI. The warm core results from the subsidence of stratospheric air associated with the detrainment of convective bursts (CBs). The upper divergent outflow appears to play an important role in protecting the warm core from ventilation by environmental flows. Results also show the development of more CBs preceding RI, but most subsidence warming radiates away by internal gravity waves and storm-relative flows. In contrast, many fewer CBs occur during RI, but more subsidence warming contributes to the balanced upper-level cyclonic circulation in the warm core (as intense as 20,,aC) region. Furthermore, considerable CB activity can still take place in the outer eyewall as the storm weakens during its eyewall replacement. Sensitivity simulations reveal that the upper-level warm core and CB activity depend critically on warm SST. We conclude that significant CB activity in the inner-core regions is an important ingredient in generating an upper-level warm core that is hydrostatically more efficient to the RI of TCs, given all the other favorable environmental conditions. The formation of a divergent upper-level outflow that prevents the warm core from ventilation is examined through asymmetric contraction processes associated with new rainbands forming inside the eyewall. The relative vorticity, generated in the downshear region and then advected cyclonically downstream, can induce convergence in the boundary layer. With the aid of high moisture content, the convergence can trigger deep convection and contribute to the formation of the new rainbands. Finally, the importance of a small eye size is demonstrated using three widely accepted approximations: angular momentum conservation, solid body rotation and gradient wind balance. Results show that the storm intensifies much faster for a given contraction speed if the eye size is small.