Unique calibration technique uncovers details of precipitation in a climate model

Apr 05, 2013
Scientists are working on new techniques to better simulate precipitation, one of the most difficult climate elements to represent in a climate model.

(Phys.org) —Not all precipitation is created equal. Using a unique uncertainty quantification (UQ) technique, scientists at Pacific Northwest National Laboratory, Scripps Institution of Oceanography, and Nanjing University calibrated the ratio between showery and stormy rain for simulations in a popular atmospheric model. Although current model results depict total precipitation fairly well, the details of precipitation type or origin does not compare well to real-life observations. The team, led by PNNL's Dr. Yun Qian, tested the sensitivity of precipitation and atmospheric circulation to several key variables used in the model. The new model results matched observations in both cases.

Precipitation is one of the most difficult climate elements to represent in a computer model. It is variable and hard to predict. Having the computational confidence to predict future based on accurate modeling of the present state is crucial. are working with computational researchers to solve this issue with a modeling technique called uncertainty quantification, or UQ (see sidebar Uncertainty Quantification). UQ can characterize, define and reduce the amount of uncertainty that may exist in a model, the data and the computation of complex climate variables. Reducing the uncertainty is critical to understanding how humans impact the global water and energy cycles now, and in the future.

The Community (CAM5) is the atmospheric component of the Community Earth System Model (CESM). The research team's objective was to investigate why model results, when separated by convective and stratiform precipitation, are very different from , though total precipitation is reasonably simulated. This disparity results in the model simulating too much convective rain compared to measurements. They postulated that the more reasonable total precipitation simulations may be due to compensating errors from several processes that are not correctly represented in the model. It is critical to calibrate the parameterizations and ensure each individual process in the climate model is accurate because the current state does not assure a reliable prediction for future climate scenarios.

The team used a stochastic importance-sampling approach to calibrate parameters in the CAM5 deep convection calculation. Their method, called the Simulated Stochastic Approximation Annealing algorithm, takes advantage of two techniques allowing the algorithm to efficiently arrive at optimal results. For the first time, the team was able to combine precipitation rates and types from two observational sources to calculate convective precipitation ratios and compare them with simulations in CAM5. They also examined the sensitivity of precipitation and circulation to key parameters in the to evaluate the impact of the improved simulations on the global circulation and climate modeling.

Where the current study focuses only on deep convection in CAM5, future studies will work on calibrating multiple processes at one time, such as turbulence, and shallow and deep convection.

Explore further: Warm US West, cold East: A 4,000-year pattern

More information: Yang, B. et al. Uncertainty Quantification and Parameter Tuning in the CAM5 Zhang-McFarlane Convection Scheme and Impact of Improved Convection on the Global Circulation and Climate. Journal of Geophysical Research Atmospheres 118:395-415. DOI:10.1029/2012JD018213.

add to favorites email to friend print save as pdf

Related Stories

Taming uncertainty in climate prediction

Mar 23, 2012

(PhysOrg.com) -- Uncertainty just became more certain. Atmospheric and computational researchers at Pacific Northwest National Laboratory used a new scientific approach called "uncertainty quantification," ...

Tropical clouds hold clues for the global water cycle

Jan 16, 2012

(PhysOrg.com) -- To study the wellspring of atmospheric water, you have to start with tropical clouds. Scientists at Pacific Northwest National Laboratory showed that global climate models are not accurately ...

A better picture of clouds

Feb 13, 2012

Some of us look at clouds and see animal shapes. Scientists are looking beyond. For the first time, a team of scientists led by Pacific Northwest National Laboratory used actual measurements of clouds and ...

Connecting the dots on aerosol details

Jul 27, 2011

Predicting future climate change hangs on understanding aerosols, considered the fine details in the atmosphere. Researchers at Pacific Northwest National Laboratory and the National Center for Atmospheric ...

Recommended for you

Warm US West, cold East: A 4,000-year pattern

1 hour ago

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...

New study outlines 'water world' theory of life's origins

4 hours ago

(Phys.org) —Life took root more than four billion years ago on our nascent Earth, a wetter and harsher place than now, bathed in sizzling ultraviolet rays. What started out as simple cells ultimately transformed ...

Agriculture's growing effects on rain

Apr 15, 2014

(Phys.org) —Increased agricultural activity is a rain taker, not a rain maker, according to researchers at Pacific Northwest National Laboratory and their collaborators at the University of California Los ...

User comments : 0

More news stories

Warm US West, cold East: A 4,000-year pattern

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...

UN weather agency warns of 'El Nino' this year

The UN weather agency Tuesday warned there was a good chance of an "El Nino" climate phenomenon in the Pacific Ocean this year, bringing droughts and heavy rainfall to the rest of the world.

ESO image: A study in scarlet

This new image from ESO's La Silla Observatory in Chile reveals a cloud of hydrogen called Gum 41. In the middle of this little-known nebula, brilliant hot young stars are giving off energetic radiation that ...

First direct observations of excitons in motion achieved

A quasiparticle called an exciton—responsible for the transfer of energy within devices such as solar cells, LEDs, and semiconductor circuits—has been understood theoretically for decades. But exciton movement within ...

Patent talk: Google sharpens contact lens vision

(Phys.org) —A report from Patent Bolt brings us one step closer to what Google may have in mind in developing smart contact lenses. According to the discussion Google is interested in the concept of contact ...

Tech giants look to skies to spread Internet

The shortest path to the Internet for some remote corners of the world may be through the skies. That is the message from US tech giants seeking to spread the online gospel to hard-to-reach regions.