Tag: climate

Fewer Southeastern Tornadoes Occur Following Dry Falls and Winters


Rainfall irregularities as observed by NASA’s Tropical Rainfall
Measurement Mission  satellite. Credit: NASA

Perhaps Dorothy, from the famed film Wizard of Oz, should have hoped for a fall or wintertime drought. According to findings from a NASA-funded study published last June in Environmental Research Letters , dry fall and winter seasons in the southeastern United States mean it is less likely that Southern twisters will develop in springtime to sweep anyone off their feet.


Using rainfall data from NASA satellites, rain gauge information, and NOAA’s Storm Prediction Center tornado record dating back to 1952, University of Georgia meteorologists Marshall Shepherd and Tom Mote and Purdue University climatologist Dev Niyogi discovered a statistical tendency for drought-ravaged fall and winter seasons to pave the way for “below normal tornado days” in spring seasons that follow.

 

“This is conceptually similar to what Bill Gray’s been doing for more than 25 years when he predicts how active the hurricane season will be based on African rain,” said Shepherd, the study’s lead author, of the Colorado State University’s pioneer hurricane season forecaster.

They culled data from Northern Georgia and other parts of the southeast, but Shepherd and his colleagues believe their findings may have relevance for other regions. The new study also adds to the body of related work Shepherd and Niyogi are ushering, including their study earlier this year in the aftermath of Atlanta’s spring 2008 twister that linked urbanization and drought to tornado activity.

For Shepherd in particular, there’s no place like home when considering the geographical focus of much of his meteorological research. “Science is my proverbial yellow brick road,” explained Shepherd. “It’s taken me down some fascinating paths, especially in learning more in recent years about tornado phenomena in my own backyard.”

 

–Gretchen Cook Anderson, NASA’s Earth Science News Team

Science Advice for an Evolving Ozone Layer Agreement


NASA scientist Paul Newman briefly stopped in Cairo, Egypt, on his way to the
Montreal Protocol meeting in Port Ghalib. Credit: Paul Newman

The view of the Red Sea was spectacular, but it was all work and no play for NASA atmospheric scientist Paul Newman during a recent trip to Port Ghalib, Egypt. That’s where scientists, policymakers, and representatives of the United Nations Environment Programme, convened Nov. 4-8 for an annual meeting to discuss and amend the Montreal Protocol — the international agreement that regulates ozone-depleting substances. Newman attended as co-chair of the Scientific Assessment Panel and gave us an inside look.

Q: Scientists use satellites and computer models to better understand the recovery of the ozone layer. How does this kind of science contribute to the policy decisions?
A: The Montreal Protocol regulates gases that destroy ozone, also known as ozone depleting substances (ODSs). The most famous of these are the chlorofluorocarbons (CFCs) that were used in spray cans and as refrigerants. Science provides that foundation for the Protocol. We used (and still use) models to predict the evolution of ozone in our atmosphere in response to the regulations made by the signatory countries. Satellite, aircraft, balloon, and ground observations provide a check on our model estimates. If you can’t simulate the past, it’s hard to claim that you can predict the future.

Q: What is involved in a typical day as “co-chair of the scientific assessment panel”?
A: We’re commonly referred to as the SAP. Not a great acronym for the scientists! In any case, we are the “on-the-spot” science advisors on all policy questions. 

In a typical day, there is a lot of discussion amongst the delegates about technical issues. Delegates actively discuss “critical use exemptions.” For example, methyl bromide is used as a fumigant. Plants, flowers, vegetables are all fumigated to help preserve them or to stop the spread of invasive species such as fruit flies. Without some sort of fumigation, entire farming industries might be destroyed. However, methyl bromide is also an ozone depleting substance. The SAP provides information on methyl bromide as an ozone depleting substance. For example, if we stop all methyl bromide usage, how much will this help the ozone layer?

Q: Why is there the need to revisit the Montreal Protocol with regular meetings?
A: The Protocol was designed to be an evolving agreement. Originally, the production of ODSs was limited, not stopped. Over the years, policymakers strengthened the original agreement such that all CFC production is now stopped. However, there is still some usage in developing countries, and there are stocks of ODSs that could potentially be destroyed. The nations get together twice per year to talk over the needs for evolving or strengthening the agreement.

Q: What are hydrofluorocarbons (HFC’s), and why do you think a proposal to include HFCs in the protocol was unsuccessful this year?
A: Hydrofluorocarbons, or HFCs, are used as refrigerants, and they don’t destroy ozone. However, HFCs are powerful greenhouse gases.

When CFCs were banned, alternative refrigerants were developed to take their place. The initial alternatives were hydrochlorofluorocarbons (HCFCs). HCFCs were still ozone depleting substances, but they had much shorter lifetimes than CFCs, and hence, were less ozone dangerous than CFCs. In 2007, the HCFCs were banned under the Montreal Protocol and are now being phased out.

HCFCs are now being replaced by HFCs. The Montreal Protocol shifted from the ozone dangerous CFCs to the less dangerous HCFCs, and now to the ozone safe HFCs. By banning CFCs, the Montreal Protocol had a double benefit: less ozone depletion and less greenhouse gas warming (CFCs are powerful greenhouse gases).

However, by banning CFCs, the Montreal Protocol created a demand for the ozone-safe HFCs (people still want air conditioners). All of the climate benefit gained by banning CFCs might be lost as HFCs increase in our atmosphere. Hence, some people are calling for the banning of HFCs under the Montreal Protocol, in spite of the fact that HFCs don’t destroy ozone. By banning HFCs, the Montreal Protocol would become both an ozone treaty and a climate treaty.

The HFC amendment did not go through for a number of reasons. The primary reason is that many countries believe that HFCs are climate related and should therefore be regulated under the Kyoto Agreement.

Q: What current research do you think could impact future meetings?
A: The Montreal Protocol is evolving into both an ozone and climate agreement. It is still necessary for scientists to investigate the impact of human-produced chemicals on both ozone and climate. Every day new chemicals are being proposed for various uses, and the scientists need to assess the environmental impact to select those chemicals that are non-toxic and environmentally safe.

–Kathryn Hansen, NASA’s Earth Science News Team

When It Rained,It Poured

Satellite image
The image shows estimates of rainfall for the southeastern United States from
September 14–21. The estimates, acquired by multiple satellites, are calibrated
with rainfall measurements from NASA’s Tropical Rainfall Measuring Mission
(TRMM)satellite. The highest rainfall amounts—more than 300 millimeters
(11.8 inches)—appear in blue. The lightest amounts appear in pale green.
Credit: NASA/Jesse Allen

For the past four years, drought has parched the soil of north Georgia farms, nearly drained Atlanta’s 38,000-acre reservoir, and left area lawns brown. Then in just eight days in September 2009, the region’s weather took a turn that likely had residents asking if they were on a climate seesaw.

 

As millions of Georgians watched and as many fled for higher ground, meteorological forces coalesced to deliver heavy rains and flooding not seen in the southeastern U.S. in more than 100 years, according to the National Weather Service.

 

Millions of dollars of property were destroyed, and ten lives were lost. The flooding dominated local TV news and compelled the governor to declare a state of emergency across 17 counties.

 

Even before the rains ended, research meteorologist, Marshall Shepherd a professor of Atmospheric Sciences at the University of Georgia, and colleagues began piecing together rainfall and soil moisture data from NASA satellites, Doppler radar, weather reports and ground-level rain gauges to assemble a clearer picture of the climatological factors that fueled the flooding.

 

Though not yet peer reviewed, Shepherd’s initial findings suggest what may have prompted the downpours and floods. Moisture from the Gulf of Mexico was drawn into the southeast by a stalled low pressure system from the Mississippi Valley. The moist air and a series of meteorological disturbances merged with a key ingredient – a dramatic increase in urban land cover – to bring this historic weather event to the region for the second time in as many years.

 

“We had days and days of downpours and an extraordinary 24-hour rainfall event at the end of that period. With soil moisture already at a high, the rain could no longer infiltrate the soil and we reached a tipping point for flooding,” explained Shepherd, a native of metropolitan Atlanta who NASA has funded to investigate how urban land cover and pollutants affect rainfall and surface water changes. 

 

“The rain and the soil moisture content combined to overwhelm rivers and streams,” he said. “Add to that Atlanta’s impenetrable roads and sidewalks, which increase the volume of runoff, and you get the event of record we witnessed.”

 

According to Shepherd, the long drought in the southeast – which caused job losses in agriculture and lawncare and other water use hardships across many sectors of society — is now over.  

 

“In fact, October is normally the driest month in North Georgia,” Shepherd said. “But this year, sea surface temperature data from NASA and NOAA satellites tell us a moderate El Nino in the Pacific appears likely to lead to a cooler and wetter fall and winter in the Southeast.”

 

Curiously, drought may be the last of Atlanta residents’ weather worries in the next season or two to come.

 

–Gretchen Cook-Anderson, NASA’s Earth Science News Team