AMS Science Preview: “Outdoor days,” lightning, air pollution
Early online research from journals of the American Meteorological Society
The American Meteorological Society continuously publishes research on climate, weather, and water in its 12 journals. Many of these articles are available for early online access–they are peer-reviewed, but not yet in their final published form.
Below is a selection of articles published early online recently. To view full article text, members of the media can contact kpflaumer@ametsoc.org for press login credentials.
Observed Changes in Extreme Precipitation Associated with United States Tropical Cyclones
Journal of Climate
Rainfall from tropical cyclones is increasing across the continental U.S. Rainfall extremes are increasing worldwide, and tropical cyclones may play a major part. A new study finds that the area of the United States exposed to extreme tropical cyclone rainfall (in which a tropical cyclone will bring five-year record rainfall) is increasing. Overall, tropical cyclones show increasing rainfall, and major hurricanes show large increases in the most extreme rainfall values. Average and maximum rainfall associated with tropical cyclones is increasing over most of the eastern U.S., especially from northern Alabama to the southern Appalachians.
How Much Lightning Actually Strikes the United States?
Bulletin of the American Meteorological Society
Mapping U.S. lightning hotspots. This study maps lightning across the contiguous United States (CONUS), and suggests that the Gulf Coast region from Florida to Texas has the highest concentration of lighting. Parts of Tornado Alley are also at high risk. The authors calculated that the CONUS receives an annual average of 23.4 million “cloud-to-ground flashes” of lightning, with 36.8 million "ground strike points" (many lightning flashes strike more than one point on the ground).
North-South Disparity in Impact of Climate Change on “Outdoor Days”
Journal of Climate
Climate warming to restrict “outdoor days” in the Global South. Studies of climate risk tend to focus on extremes, but changes in the availability of mild weather are equally important. Based on high-emissions scenarios using two different climate models, days in which temperatures are comfortable for outdoor activities (“outdoor days,” defined as 10°C to 25°C) are set to grow fewer in the future for people living in developing countries–especially near the equator. Meanwhile, developed countries in the middle and high latitudes could see more “outdoor days” due to a reduction in cold weather in fall, winter, and spring.
The Impacts of Heat and Air Pollution on Mortality in the United States
Weather, Climate, and Society
Air pollution increases mortality risks from heat. Using 2001–2011 data from across the United States, the authors find that extreme heat and PM2.5 air pollution jointly increase mortality; estimates of heat-related mortality that do not take air pollution into account may overestimate the effects of heat alone. Government programs that reduce air pollution or urban heat, even by a small amount, could lead to significant reductions in heat and pollution related mortality. Results also show that wind-driven pollution from nearby areas and wildfires increases mortality, especially during periods of extreme heat.
Substantial Warming of the Atlantic Ocean in CMIP6 Models
Journal of Climate
Why is the Atlantic Ocean heating up faster than the Pacific? Observations of Atlantic Ocean warming since 1960 show that the average warming rate near the surface is almost three times as strong as it is in the Pacific. Climate models suggest that, in addition to a slowdown in deep ocean circulation patterns, this heating may be due to atmospheric circulation patterns shifting poleward, plus a recent reduction in anthropogenic aerosols and clouds over the Northern Hemisphere—resulting in reduced surface wind speed and less cloudiness over the mid-latitude oceans. Because the Atlantic is wider in the mid-latitudes and narrower in the tropics, more of it is exposed to these heating patterns.
The Rise of Data-Driven Weather Forecasting: A First Statistical Assessment of Machine Learning-Based Weather Forecasts in an Operational-Like Context
Bulletin of the American Meteorological Society
AI weather forecasts are looking promising. Machine learning models are emerging as a promising tool to create weather forecasts faster and with less computational cost. This study is the first to compare forecasts generated by a new machine learning model against standard forecasts using numerical weather prediction. For forecasts three days out, the machine-learning PanguWeather (PGW) model performed better than or equal to existing high-quality forecast models, although it still showed some limitations.
Assessing Regional-scale Heterogeneity in Blue-Green Water Availability under 1.5°C Global Warming Scenario
Journal of Applied Meteorology and Climatology
Even 1.5°C warming may greatly impact water for regions like rice-growing central India. Examining the effects of a 1.5°C global average warming on regional water and temperature in India’s rice-growing Mahanadi Basin found that availability of both blue water (stored in lakes, aquifers, reservoirs, etc.) and green water (in soil and plants) would likely decline. Depending on the climate model and future adaptation strategies, green water could decline by up to 12%, and blue water by up to 40%—potentially catastrophic for an agriculturally important region.
The Relative Importance of Antarctic Sea-Ice Loss Within the Response to Greenhouse Warming
Journal of Climate
Loss of Antarctic ice might play a larger role in changing climate patterns. A study modeling global climate responses to the loss of sea ice at both poles found that the loss of Antarctic sea ice appeared to have more control over the global response to greenhouse warming than Arctic sea-ice loss. Effects of Antarctic ice loss in the model include shifting ocean salinity, precipitation and temperature changes that extend all the way up to the tropics and even the far Northern Hemisphere.
Exploring the Factors Controlling the Annual Range of Amazon Precipitation
Journal of Climate
Sea-surface temperature is dominant factor in increasing seasonal rain extremes in the Amazon. Wet seasons in the Amazon rainforest are getting wetter, and dry seasons drier. This study used a climate model to investigate whether global warming, ocean temperature variability, or the impact of deforestation is the more likely culprit. It found that North Atlantic sea surface warming—due to both natural variability and global warming—is the key factor in the increased range in Amazon precipitation from 1979 to 2014.
How Much Does Land-Atmosphere Coupling Influence Summertime Temperature Variability in the Western United States?
Journal of Climate
Lack of winter rain contributes to summer heat in U.S. West. According to a new modeling study, deficits in soil moisture—driven by a downward trend in winter precipitation in the Southwest since 1981—are responsible for 40% of the observed trend of warmer weather in the western U.S. Lack of precipitation in preceding seasons leads to less soil moisture, which affects humidity and temperature during the summer.
The Southern African Heat Low: Structure, Seasonal and Diurnal Variability, and Climatological Trends
Journal of Climate
Low-pressure system associated with dry weather is increasingly affecting southern Africa. A heat-driven area of low pressure that forms in the lower atmosphere during summers in southern Africa, is associated with below-average rainfall continent-wide. This paper better documents the heat low, and finds that the frequency of strong heat lows has rapidly increased, with more strong heat lows in 2014–2019 than in the entire 30-year period from 1960 to 1989. This heat low will likely continue to play an important role in precipitation changes in southern Africa due to climate change.
Impact of ENSO and Trends on the Distribution of North American Wintertime Daily Temperature
Journal of Climate
Global warming and ENSO exert major control over North American winter temperature patterns. Climate change trends and the El Niño–Southern Oscillation (ENSO, the Pacific Ocean cycle that brings El Niño and La Niña) are responsible for much of the year-to-year changes in where higher and lower daily winter temperatures happen across North America, according to a new statistical analysis. Warm ENSO conditions (El Niño) result in higher median temperatures and a smaller temperature range in central-northern North America. In the southern U.S., cool ENSO conditions (La Niña) actually shift winter daily temperatures warmer.
A Stochastic Statistical Model for U.S. Outbreak-level Tornado Occurrence based on the Large-scale Environment
Monthly Weather Review
A new index tracks upward trends in tornado outbreak risk. The authors created a model and “tornado outbreak index” to predict the risk of tornado outbreaks (when multiple tornadoes occur within a short period of time) based on climate variables. “Storm relative helicity” (indicating the potential for rotation within a storm updraft) was an especially important variable for predicting outbreaks. In agreement between the models and observed data, the number of winter-spring tornado outbreaks has increased since 1979, and El Niño-La Niña cycles are linked to winter-spring tornado outbreak activity over the Ohio River Valley and Tennessee River Valley.
Nonequilibrium Fluctuations of Global Warming
Journal of Climate
Global warming may follow “small system” rules. The authors note similarities between the complicated way the Earth system responds to global warming and the behavior of microscopic systems described by statistical mechanics. Using similar rules to model global warming responses helps explain, for example, the increased variability in global temperature extremes, which you’d also expect to see in microscopic systems that are out of equilibrium. Using this lens could provide a new way to analyze climate data and assess predictions from climate models.
You can view all research published in AMS Journals at journals.ametsoc.org.
About the American Meteorological Society
The American Meteorological Society advances the atmospheric and related sciences, technologies, applications, and services for the benefit of society. Founded in 1919, AMS has a membership of around 12,000 professionals, students, and weather enthusiasts. AMS publishes 12 atmospheric and related oceanic and hydrologic science journals; hosts more than 12 conferences annually; and offers numerous programs and services. Visit us at www.ametsoc.org/.
About AMS Journals
The American Meteorological Society continuously publishes research on climate, weather, and water in its 12 journals. Some AMS journals are open access. Media login credentials are available for subscription journals. Journals include the Bulletin of the American Meteorolocial Society, Weather, Climate, and Society, the Journal of Climate, and Monthly Weather Review.
JOURNAL
Journal of Climate
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