Dr. Jiwen Fan is a climate physics scientist at Pacific Northwest National Laboratory. Her current research work focuses on aerosol effects on cloud processes and associated climate effects by combining modeling simulations with in-situ and remote-sensing observations.
New climate research reveals how wind shear -- the same atmospheric conditions that cause bumpy airplane rides -- affects how pollution contributes to isolated thunderstorm clouds. Under strong wind shear conditions, pollution hampers thunderhead formation. But with weak wind shear, pollution does the opposite and makes storms stronger.
What problem were you setting out to solve with your research?
We wanted to research what factors--if any--determine how aerosol pollution changes convection strength in deep convective clouds (DCCs, or thunderclouds). Past research into aerosol effects on thunderclouds has provided contradictory results, none of which systematically assess the determining factors. Our purpose is to explore these factors.
What are your chief findings?
We found that the key factor is wind shear. Wind shear determines whether aerosols increase or decrease thunderstorm strength. In conditions with a strong wind shear, pollution weakens thunderstorms. But in situations with weak wind shear, the effects of pollution are opposite, leading to even stronger storms.
How are these findings applicable to climate change projections, especially in China?
Previous climate models have not taken into account aerosol effects on DCCs because this type of effect is very difficult to parameterize. Our discovery of a determining factor might help with this parameterization. In China, because pollution is bad, aerosols would have larger effect on clouds. This finding would decrease the uncertainty of aerosol effects on climate change, and increase the reliability of climate change prediction.
What are the practical implications of your research?
Practical implications might be that this research can provide some guidelines regarding pollution effects on local climate and rainfall, especially in those places that have frequent afternoon showers-- for example China’s south and east, the American southeast, and northeastern Australia. We can now decide, based upon regional prevailing wind shear, how pollution will change the weather and rainfall in that region.
What is the next step for your research?
The next step of our research is to analyze which levels of wind shear have the strongest effects, those that originate at low levels or those that originate at middle levels? The wind shear that we considered was from ground level to seven kilometers. Also, we will try to analyze the observational data from DOE ARM field campaigns to find some observational evidence in the real atmosphere. Finally, we will further explore the role of wind shear in how pollution changes weather systems such as monsoons and squall lines.
These are Dr. Jiwen Fan's written remarks. Please refer to the video interview for exact quotes.
Related Research Papers
Dominant role by vertical wind shear in regulating aerosol effects on deep convective clouds
Press release: Pollution alters isolated thunderstorms