Engineering topics

Faluvegi, G.

Publications and source records attributed to Faluvegi, G..

22 records · Page 2

NASA NTRS2012

Precipitation Response to Regional Radiative Forcing

Precipitation shifts can have large impacts on human society and ecosystems. Many aspects of how inhomogeneous radiative forcings influence precipitation remain unclear, however. Here we investigate regional precipitation responses to various forcings imposed in different latitude bands in a climate model. We find that several regions show strong, significant responses to most forcings, but that the magnitude and even the sign depends upon the forcing location and type. Aerosol and ozone forcings typically induce larger responses than equivalent carbon dioxide (CO2) forcing, and the influence of remote forcings often outweighs that of local forcings. Consistent with this, ozone and especially aerosols contribute greatly to precipitation changes over the Sahel and South and East Asia in historical simulations, and inclusion of aerosols greatly increases the agreement with observed trends in these areas, which cannot be attributed to either greenhouse gases or natural forcings. Estimates of precipitation responses derived from multiplying our Regional Precipitation Potentials (RPP; the response per unit forcing relationships) by historical forcings typically capture the actual response in full transient climate simulations fairly well, suggesting that these relationships may provide useful metrics. The strong sensitivity to aerosol and ozone forcing suggests that although some air quality improvements may unmask greenhouse gas-induced warming, they have large benefits for reducing regional disruption of the hydrologic cycle.

Shindell, D. T.↗

NASA NTRS2011

Global Multi-Year O3-CO Correlation Patterns from Models and TES Satellite Observations

The correlation between measured tropospheric ozone (O3) and carbon monoxide (CO) has been used extensively in tropospheric chemistry studies to explore the photochemical characteristics of different regions and to evaluate the ability of models to capture these characteristics. Here, we present the first study that uses multi-year, global, vertically resolved, simultaneous and collocated O3 and CO satellite (Tropospheric Emission Spectrometer) measurements, to determine this correlation in the middle/lower free troposphere for two different seasons, and to evaluate two chemistry-climate models. We find results that are fairly robust across different years, altitudes and timescales considered, which indicates that the correlation maps presented here could be used in future model evaluations. The highest positive correlations (around 0.8) are found in the northern Pacific during summer, which is a common feature in the observations and the G-PUCCINI model. We make quantitative comparisons between the models using a single-figure metric (C), which we define as the correlation coefficient between the modeled and the observed O3-CO correlations for different regions of the globe. On a global scale, the G-PUCCINI model shows a good performance in the summer (C =0.71) and a satisfactory performance in the winter (C = 0.52). It captures midlatitude features very well, especially in the summer, whereas the performance in regions like South America or Central Africa is weaker. The UKCA model (C = 0.46/0.15 for July-August/December-January on a global scale) performs better in certain regions, such as the tropics in winter, and it captures some of the broad characteristics of summer extratropical correlations, but it systematically underestimates the O3-CO correlations over much of the globe. It is noteworthy that the correlations look very different in the two models, even though the ozone distributions are similar. This demonstrates that this technique provides a powerful global constraint for understanding modeled tropospheric chemical processes. We investigated the sources of the correlations by performing a series of sensitivity experiments. In these, the sign of the correlation is, in most cases, insensitive to removing different individual emissions, but its magnitude changes downwind of emission regions when applying such perturbations. Interestingly, we find that the O3-CO correlation does not solely reflect the strength of O3 photochemical production, as often assumed by earlier studies, but is more complicated and may reflect a mixture of different processes such as transport.

Voulgarakis, A.↗

NASA NTRS2010

The Net Climate Impact of Coal-Fired Power Plant Emissions

Coal-fired power plants influence climate via both the emission of long-lived carbon dioxide (CO2) and short-lived ozone and aerosol precursors. Using a climate model, we perform the first study of the spatial and temporal pattern of radiative forcing specifically for coal plant emissions. Without substantial pollution controls, we find that near-term net global mean climate forcing is negative due to the well-known aerosol masking of the effects of CO2. Imposition of pollution controls on sulfur dioxide and nitrogen oxides leads to a rapid realization of the full positive forcing from CO2, however. Long-term global mean forcing from stable (constant) emissions is positive regardless of pollution controls. Emissions from coal-fired power plants until 1970, including roughly 1/3 of total anthropogenic CO2 emissions, likely contributed little net global mean climate forcing during that period though they may have induce weak Northern Hemisphere mid-latitude (NHml) cooling. After that time many areas imposed pollution controls or switched to low sulfur coal. Hence forcing due to emissions from 1970 to 2000 and CO2 emitted previously was strongly positive and contributed to rapid global and especially NHml warming. Most recently, new construction in China and India has increased rapidly with minimal application of pollution controls. Continuation of this trend would add negative near-term global mean climate forcing but severely degrade air quality. Conversely, following the Western and Japanese pattern of imposing air quality pollution controls at a later time could accelerate future warming rates, especially at NHmls. More broadly, our results indicate that due to spatial and temporal inhomogeneities in forcing, climate impacts of multi-pollutant emissions can vary strongly from region to region and can include substantial effects on maximum rate-of-change, neither of which are captured by commonly used global metrics. The method we introduce here to estimate regional temperature responses may provide additional insight.

Shindell, D.↗

NASA NTRS2003

Climate Impacts on Tropospheric Ozone and Hydroxyl

Climate change may influence tropospheric ozone and OH via several main pathways: (1) altering chemistry via temperature and humidity changes, (2) changing ozone and precursor sources via surface emissions, stratosphere-troposphere exchange, and light- ning, and (3) affecting trace gas sinks via the hydrological cycle and dry deposition. We report results from a set of coupled chemistry-climate model simulations designed to systematically study these effects. We compare the various effects with one another and with past and projected future changes in anthropogenic and natural emissions of ozone precursors. We find that white the overall impact of climate on ozone is probably small compared to emission changes, some significant seasonal and regional effects are apparent. The global effect on hydroxyl is quite large, however, similar in size to the effect of emission changes. Additionally, we show that many of the chemistry-climate links that are not yet adequately modeled are potentially important.

Shindell, Drew T.↗