Using weather balloons to improve understanding of how surface conditions may impact clouds and rain
This summer, researchers are launching an unprecedented number of weather balloons in rural Oklahoma to collect data to help improve how weather and climate models predict the diurnal cycle of rainfall and cloud development.
A diurnal cycle is any pattern that recurs every 24 hours as a result of one full rotation of the Earth with respect to the sun. In climatology, the diurnal cycle is one of the most basic forms of climate patterns, yet can be a challenge for weather and climate models to get right. The diurnal cycles of surface temperature, humidity, and rainfall are the result of complex interactions between the land surface and the lowest levels of the atmosphere.
“The diurnal cycle of rainfall and cloud development has a sizable impact on our ability to predict climate and the duration and severity of extremes, such as floods and drought,” said Craig Ferguson, a research assistant professor at the University at Albany’s Atmospheric Sciences Research Center in New York and the lead investigator for the field research campaign Enhanced Soundings for Local Coupling Studies.
Climate models are challenged with accurately predicting the timing and amplitude of the cycle because rain during the day versus night has different interactions with the land. For example, precipitation that is too frequent, too light, and peaks during daytime leads to increased infiltration and reduced runoff, enhanced evapotranspiration, and accelerates soil moisture dry-down.
“Over time,” Ferguson explained, “this plays a big role on the ability of a climate model to predict the persistence of drought and rain events.”
“To challenge the models,” he said, “we want a data set spanning multiple days that provides high temporal and vertical resolution of the atmosphere from the early morning hours to the end of day, and we are targeting days with synoptic [view at a common point] conditions that are conducive to local land affects.”
Gold Standard for Profiling
To get these data, Ferguson and co-investigators, Pierre Gentine from Columbia University in New York and Joseph Santanello from NASA’s Goddard Space Flight Center in Maryland, will select 12 campaign days between June 15 and August 31 to augment operational radiosonde launches at the Southern Great Plains (SGP), the premier field measurement site of the Atmospheric Radiation Measurement (ARM) Climate Research Facility.
“The radiosonde is still the gold standard for profiling from the land’s surface to the highest levels of atmosphere,” Ferguson said.
Due to their expense, radiosondes are typically only launched every 6 hours at the ARM SGP site and every 12 hours at the 102 National Weather Service sites nationally. To get a more robust data set, the Enhanced Soundings researchers will launch radiosondes hourly from 6:30 am to 6:30 pm. At 3-hour intervals a duplicate “trailer” radiosonde will be launched 10 minutes later to make sure a representative profile of the atmosphere is being captured. A single launch at 3:30 am will correspond with the nighttime overpass of the NASA Afternoon Earth-observing satellite constellation (A-Train) that includes the Atmospheric Infrared Sounder (AIRS), which estimates atmospheric profiles of temperature and humidity by remote sensing.
In total, 19 balloons will be launched on each research day, including the 4 that are launched daily at the ARM site. The selected days that the balloons will be launched are determined by the investigators by 7 am on the preceding day, taking into consideration daily weather forecasts and the operability of complimentary ARM instrumentation.
Big Research Impact
An overarching goal of the Enhanced Soundings campaign is to address how ARM could better observe land-atmosphere interactions and coupling to support the evaluation and refinement of coupled weather and climate models.
The study is running at the SGP concurrently with—and its results will be complimentary to—the Plains Elevated Convection at Night (PECAN), a multi-agency research campaign using airborne, and fixed and mobile ground instrumentation to take detailed measurements of what triggers clouds and precipitation at night.
There is evidence that the initial development of the nocturnal boundary layer strongly depends on the characteristics of the daytime boundary layer, and both the Enhanced Coupling campaign and 24/7 operations of the Atmospheric Emitted Radiance Interferometers (AERIs) during PECAN will provide data to investigate this hypothesis. These two data sets will provide scientists with a rich description of the full diurnal cycle of the atmosphere to study for many years to come.
# # #
The ARM Climate Research Facility is a national scientific user facility funded through the U.S. Department of Energy’s Office of Science. The ARM Facility is operated by nine Department of Energy national laboratories, including Argonne National Laboratory, which manages the SGP site.