Beate Liepert's Web Site / Research Interests

Research Interests

My general interests are understanding climate variability from millennial to decadal time scales. I like working on interdisciplinary projects and on the edges of my field of expertise - atmospheric physics.

"Global Dimming"

The amount of solar energy that reaches the surface of the Earth declined significantly, about 1-2% per decade, during the 20th century. This decline was measured at stations around the world. The reductions were caused by cloud variations presumably triggered by global warming and by increases in man-made (or anthropogenic) concentrations of aerosols (tiny particles in the air), which reflect more sunlight. Global-scale cloud changes are due to natural variability (El Niño), water vapor increases in a warmer world, and increasing concentrations of aerosol particles that act as cloud condensation nuclei. Major volcanic eruptions also inject large amounts of aerosol particles into the atmosphere, which disturb the radiative balance of the Earth for several years.

Global Energy Budget and the Water Cycle

Global dimming masks part of the global warming signal. Reducing the emissions of anthropogenic aerosols, a key cause of "dimming," would accelerate global warming. Global dimming is largely a surface phenomenon that acts by reducing the energy needed for evaporation, the driving force of the water cycle. (Liepert et al.) Animation >>

Asian Monsoonal System and Anthropogenic Impacts

Increased greenhouse gas and aerosol concentrations may lead to contrasting surface temperature disturbances over the Eurasian continent and the Indian Ocean. These cooling and warming patterns have the potential to trigger typical dynamical responses in the monsoonal system and rainfall pattern. This study is a collaborative project with my colleague Alessandra Giannini from IRI.

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			Research Interests My general interests are understanding climate variability from millennial to decadal time scales. I like working on interdisciplinary projects and on the edges of my field of expertise - atmospheric physics. "Global Dimming" The amount of solar energy that reaches the surface of the Earth declined significantly, about 1-2% per decade, during the 20th century. This decline was measured at stations around the world. The reductions were caused by cloud variations presumably triggered by global warming and by increases in man-made (or anthropogenic) concentrations of aerosols (tiny particles in the air), which reflect more sunlight. Global-scale cloud changes are due to natural variability (El Niño), water vapor increases in a warmer world, and increasing concentrations of aerosol particles that act as cloud condensation nuclei. Major volcanic eruptions also inject large amounts of aerosol particles into the atmosphere, which disturb the radiative balance of the Earth for several years. What is global dimming and how does it affect climate? Read more >> Global Energy Budget and the Water Cycle Global dimming masks part of the global warming signal. Reducing the emissions of anthropogenic aerosols, a key cause of "dimming," would accelerate global warming. Global dimming is largely a surface phenomenon that acts by reducing the energy needed for evaporation, the driving force of the water cycle. (Liepert et al.) Animation >> Local Field Campaigns in the New York Metropolitan Area Manhattan Summer 2003: Spatial variability of atmospheric turbidity and air pollution in New York City. A project of NASA GISS Institute for Planets and Climate for high school students of New York City public schools. Hudson River Project: Spectral measurements of atmospheric transparency, ozone, and water vapor profiles at Lamont Observatory. Read more >> Pittstown, New Jersey, Summer 2004: Balloon flights. In this proof of concept study we measured vertical profiles of aerosol properties on board a hot-air balloon over the New York and Philadelphia areas. This was an inexpensive and effective alternative to airplane measurements which could be adapted to other parts of the world. At higher altitudes, aerosol particles can be transported on continental scales. By contrast, boundary-layer aerosols are mostly a local phenomenon. Vertical profiles of physical and radiative properties are needed to learn about transport processes and to assess theoretical atmospheric simulations and satellite retrievals. Asian Monsoonal System and Anthropogenic Impacts Increased greenhouse gas and aerosol concentrations may lead to contrasting surface temperature disturbances over the Eurasian continent and the Indian Ocean. These cooling and warming patterns have the potential to trigger typical dynamical responses in the monsoonal system and rainfall pattern. This study is a collaborative project with my colleague Alessandra Giannini from IRI. Climate Model Analyses 20th century global dimming is a robust result in simulations of coupled atmosphere-ocean general circulation models - A contribution to the Intergovernmental Panel on Climatic Change 4th Assessment Report (Romanou et al., 2007). Read NASA research news. The longterm variation of tropospheric aerosol concentrations by fossil fuel burning has been simulated by NASA GISS scientists. The model underestimates the effects of anthropogenic aerosols on atmospheric solar absorptivity if compared to observations in the U.S. and in Germany (Liepert and Tegen, 2002). A study on aerosol cloud interactions. The indirect effects of aerosols on cloud lifetime, cloud transmissivity and precipitation suppression were compared in GCM simulations and observations (Liepert and Lohmann, 2001). Significant discrepancies in clear sky shortwave fluxes between models and observations were detected by Wild and Liepert (1999).
	© 2006 Dr. Beate Liepert