Scientific Objectives and Observational Strategy for 2017 North American Solar Eclipse Project. (January, 2017)

Size: px

Start display at page:

Download "Scientific Objectives and Observational Strategy for 2017 North American Solar Eclipse Project. (January, 2017)"

Virginia Davis
6 years ago
Views:

1 Scientific Objectives and Observational Strategy for 2017 North American Solar Eclipse Project (January, 2017) Members of the NASA National Space Grant College and Fellowship Program and NSF EPSCoR program will undertake comprehensive atmospheric observations of the total solar eclipse across North America on August 21, Total eclipses are rare and very impactful events. For those who have witnessed them, it is a memory they keep forever. The continental US hasn t had a total eclipse since 1979 (northwest only). The 2017 eclipse is therefore perfect opportunity for study that should not be passed up. The 2017 eclipse totality starts on the Oregon coast at about 1:20 PM Eastern on August 21, 2017 and ends about 2:50 PM Eastern on the South Carolina coast. Observational components for this project include coordinated radiosonde measurements across the entire path and comprehensive ground and upper atmospheric observing facilities located at the following currently identified strategic locations; Madras, Oregon, Glendo,, St Louis, Missouri, Fort Campbell, Kentucky and Franklin, North Carolina. This white paper describes the scientific objectives of the St. Louis experimental array that serves as the example for the other participating facilities. The objectives are motivated by specific meteorological questions, particularly Participant institutes Locations 1 State University of New York at, NY Albany 2 University of Montana 3 University of Maryland Baltimore Missouri County 4 St. Louis University Missouri 5 Western Kentucky University Kentucky 6 University of Virginia North Carolina University of Alabama in Huntsville San Jose State University University of Arkansas at Pine Bluff University of Delaware University of Alaska Fairbanks Miles Community College Center for Severe Weather Research Chief Dull Knife College Aaniiih Nakoda College Frenchtown High School Billings High School University of Missouri University of Illinois Saint Louis High School University of North Carolina Asheville Kentucky Oregon Kentucky North Carolina Oregon Missouri Missouri Missouri North Carolina 22 University of Delaware North Carolina 23 University of South Carolina those that concern surface and boundary layer changes immediately before, during and after eclipse totality. The paper includes a schematic of the proposed St. Louis ground and upper-air sampling network. South Carolina

2 I. Characteristic Range of Atmospheric Responses to Path of Totality (Moon s Shadow) A review of the scientific literature reveals a very limited number of atmospheric eclipse studies worldwide. However, the documented effects are wide- ranging, with atmospheric thermal changes being most prominent, ranging from the soil substrate upward through the ionosphere. There are variations in the ground- level wind, cloud cover and precipitation, and total column ozone. Additionally, a few studies have focused on generation of stratospheric gravity waves emanating from the supersonic path of the Moon s shadow across the Earth. Finally, reduced concentrations of electrons and other ions have been documented in the ionosphere. In short, there is a transient yet substantial set of responses in the thermal and kinematic atmospheric fields that develop at a much more rapid rate compared with the normal diurnal cycle. A. Surface Meteorological Changes The surface air temperature decreases up to and beyond the mid- point of totality, ranging in magnitude from - 2 to - 10 C departure from baseline (depending on season, latitude, ambient cloud cover, and degree of solar annularity). The thermal minimum lags behind the mid- eclipse point by 7-17 minutes. Smaller temperature reductions extend upward through the surface layer. The nature of the underlying surface (grass, bare soil, water) seems to influence the magnitude of the observed temperature drop. The decrease in temperature and development of a shallow inversion leads to decoupling of the wind field from surface friction. Several studies have noted a slight decrease in intensity of the mean wind, along with reduced gust factor (diminished turbulence). The notion of an eclipse wind appears to be a specious aspect, with very little scientific evidence to support its occurrence. The wind may be largely a subjective perception, due to enhanced wind- chill (from the combination of residual wind and the abrupt temperature drop). However, in areas of significant orography, the development of downslope density- current type flows, or enhancement of lake/sea breeze, may locally freshen the wind. These types of local enhancements would be less noticeable in the presence of a significant synoptic- driven, gradient wind. B. Free Tropospheric and Stratospheric Changes Radiosonde studies of eclipse weather are quite rare; the few observations available (tropical India during 2010 and 2006 in northern Africa, and central Asia) document both boundary layer and deep- layer decreases in air temperature. During the 2006 springtime eclipse, rapid loss of turbulent mixing hastened vertical shrinkage of boundary layer depth. Tropospheric cooling of a few C extended up to 15 km altitude, with reductions as large as 15 C between km. Other studies have observed abrupt stratospheric warming, up to 7 C. Less attention in the

literature seems devoted to variations in tropospheric humidity and winds during a solar eclipse. C. Cloud Cover and Precipitation Cloud cover responds to path of totality in an interesting manner.

3 literature seems devoted to variations in tropospheric humidity and winds during a solar eclipse. C. Cloud Cover and Precipitation Cloud cover responds to path of totality in an interesting manner. Satellite images over tropical South America revealed pronounced aerial reduction of shallow- moderate convective cloud within the path of totality, and the development of shallow fog layers over cool water surfaces. An Oklahoma study indicated a 35% decline in cumulus cloudiness that persisted more than an hour beyond mid- eclipse. If the troposphere is sufficiently moist, stratiform cloud layers can develop, or existing stratus layers can thicken. Finally, there is radar evidence that deep, precipitating convective clouds temporarily weaken, but do not dissipate, within the path of totality. II. Observation Strategy and Scientific Objectives: St. Louis, MO Example A. Proposed Network The entire solar eclipse spans approximately three hours with the most significant decline confined to a 90-minute period. Totality lasts about 2.5 minutes at longest duration in Thus, the execution phase of any multi-platform sampling experiment must be well-rehearsed, with contingency and redundancy, in order to maximize data collection throughout the rapidlyevolving eclipse event. Our strategy is to combine a dense ground observation network with multiple radiosonde sites, located within and along the margins of the path of totality. The central radiosonde site will be capable of very rapid, serial sonde deployment. The ground stations are autonomous data collection systems, while the radiosondes require expert crewing. Real-time network monitoring, crew coordination and data flow will be centralized and managed by scientific staff experienced in running atmospheric field campaigns. A diagram of the proposed network is shown below. The Amaren/SLU mesonet, centered on the path of totality provides mapping of surface temperature, humidity, pressure and wind responses at the ground. Several of the sites will be outfitted with solar pyrheliometers to track instantaneous variations in solar flux. Multiple sites are desirable in the event of partly cloudy conditions.

Radiosondes will be released according to two sampling modes. The spatial sampling mode seeks to understand cross-eclipse track variations in boundary layer and tropospheric temperature.

The temporal sampling mode is based on highfrequency balloon releases at the center-of-totality launch site, just minutes apart during the eclipse mid-point.

Neighboring NOAA (NWS) operational radiosonde site at Springfield, MO (WSFO) will be encouraged to participate in the launching of special sondes, timed for release during totality, pending

4 Radiosondes will be released according to two sampling modes. The spatial sampling mode seeks to understand cross-eclipse track variations in boundary layer and tropospheric temperature. Coordinated sets of launches will be made before, during and immediately after totality. The sampling interval will be chosen to sample the entire, multi-hour evolution of the eclipse. The temporal sampling mode is based on highfrequency balloon releases at the center-of-totality launch site, just minutes apart during the eclipse mid-point. Frequent sampling must also continue in the hour after mid-point, since the peak thermal and wind responses will likely lag the solar minimum by several tens of minutes. Neighboring NOAA (NWS) operational radiosonde site at Springfield, MO (WSFO) will be encouraged to participate in the launching of special sondes, timed for release during totality, pending availability of expendables. In this way, the St. Louis site s observations can be placed in the context of the broader (penumbral) gradients of temperature. Our team includes personnel with significant experience in the quality control of radiosonde datasets, including bias detection and the merging of radiosonde observations from different vendors. Central(site(( North(site(( South(site(( Ameren/SLU(Mesonet( Totality( (~50(miles)( 1st Contact 10min after 1st 2nd contact Totality 3rd contact 4th contact Central S1 S2 S3 S4 S1 S2 North S5 S5 S5 South S6 S6 S6 *"Minimum"6/4"sounding"systems"for"all"three"sites"or"only"central"site" B. Core Scientific Questions and Objectives

5 1. What is the magnitude of the temperature drop at the surface, in the boundary layer, troposphere and lower stratosphere? How much time lag is there between the temperature minimum and minimum in solar flux? At which altitude(s) is the temperature variation the largest? Does the cooling and subsequent re- warming signal exhibit vertical propagation? 2. How do temperature reductions vary across the path of totality? Is the response fairly uniform or do asymmetries arise? How far into the penumbral zone do detectable temperature variations extend? 3. How does surface temperature vary within the spatial domain of the path of totality, on fine scales, given variations in land surface cover (grass, cropland, forest, bare soil, urban surface, water i.e. Mississippi, Missouri Rivers)? 4. What is the response of the surface wind field within the path of totality? Does one observe a reduction in mean wind, as well as gust factor (turbulence)? Is the kinematic response instantaneous or time- lagged to the thermal response? 5. Does a low- level jet develop above the surface layer, in response to frictional decoupling, similar to that observed in the nocturnal boundary layer? 6. Is there evidence for terrain- induced wind circulations, as a result of cool, downslope flows i.e. valley wind developing within the river terraces of the Mississippi and Missouri Rivers? Is a mesoscale breeze generated between the St. Louis heat island and surrounding cool countryside? 7. How does cloud cover respond to changes in the boundary layer thermal forcing? If cumulus fields are present during the eclipse, is there a documentable decrease in areal extent/height/vigor of convection? Does a fog or stratus layer form within the large river valleys/floodplains? 8. Can the regional- scale effects described above be simulated using a mesoscale model such as the WRF? What additional scientific (process study) understanding can be gleaned from high- resolution simulations? 9. How are the findings above for the 2017 eclipse compared to that for prior events in other places and to that from other sites (KY and ID)? 10. How are the findings from SLU mesonet compared to that from other mesonets, such as KY an NY mesonets? III. Sustainability The core scientific questions and objectives will be addressed following the eclipse measurements with collaborative research and publications. The data will be centrally located and quality controlled for access by all participants in the field

6 campaign and by the public later on. In an effort to increase the number of ground and upper atmospheric observing facilities participating in the eclipse event, we offered a readiness activity during Summer 2016 that was interdisciplinary with a focus on scientists, undergraduate students and citizen scientists not trained formally in meteorology. We will thus demonstrate how a flexible data collection network blending surface and upper air data collection sites and management can be coordinated quickly in an on- demand request to address extreme and unique geophysical phenomena in the future that have lasting impacts on agriculture, infrastructure, transportation, human life, and property. This is an opportunity to address the effect of high temporal and spatial resolution data (which is void from our current operational network) on our understanding and forecasting of weather and climate. Such data sets are a valuable asset in years to come as we continue to build our earth s climate record. IV. References Amiridis, V., Melas, D., Balis, D.S., Papayannis, A., Founda, D., Katragkou, E., Giannakaki, E., Mamouri, R.E., Gerasopoulos, E. and Zerefos, C., Aerosol Lidar observations and model calculations of the Planetary Boundary Layer evolution over Greece, during the March 2006 Total Solar Eclipse.Atmospheric Chemistry and Physics, 7(24), pp Anderson J and West J, Climate and Weather for Celestial Events, Anderson, R. C., Keefer, D. R. and Myers, 0. E., 1972: Atmospheric pressure and temperature changes during the 7 March 1970 solar eclipse. J.Atmos. Sci., 29, pp Anfossi, D., Schayes, G., Degrazia, G., and Goulart, A.: Atmospheric turbulence decay during the solar total eclipse of 11 Au-gust 1999, Bound.-Lay. Meteorol., 111, , Aplin, K.L. and Harrison, R.G., 2003, February. Meteorological effects of the eclipse of 11 August 1999 in cloudy and clear conditions. In Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences (Vol. 459, No. 2030, pp ). The Royal Society. Eaton, F.D., Hines, J.R., Hatch, W.H., Cionco, R.M., Byers, J., Garvey, D. and Miller, D.R., Solar eclipse effects observed in the planetary boundary layer over a desert. Boundary-Layer Meteorology, 83(2), pp Espenak F, Eclipse Predictions, NASA's GSFC,

7 Figure 5 Untitled illustration of cloud fraction. Retrieved 2016 Data Source Founda, D., Melas, D., Lykoudis, S., Lisaridis, I., Gerasopoulos, E., Kouvarakis, G., Petrakis, M. and Zerefos, C., The effect of the total solar eclipse of 29 March 2006 on meteorological variables in Greece.Atmospheric Chemistry and Physics, 7(21), pp Hanna, E., Meteorological effects of the solar eclipse of 11 August Weather, 55(12), pp Harrison R. Giles, and Hanna, Edward, The solar eclipse: a natural meteorological experiment. Philosophical Transactions of The Royal Society A, 374(2077), DOI: /rsta Marlton G. J., Williams P. D., Nicoll K. A., On the detection and attribution of gravity waves generated by the 20 March 2015 solar eclipse. Philosophical Transactions of The Royal Society A, 374(2077), DOI: /rsta Montornes A., Codina B., Zack J., and Sola Y., Implementation of Bessel s method for solar eclipses prediction in the WRF-ARW model, Atmos. Chem. Phys., 16, Ramchandran, P.M., Ramchandran, R., Gupta, K.S., Patil, S.M. and Jadhav, P.N., Atmospheric surface-layer processes during the total solar eclipse of 11 August Boundary- layer meteorology, 104(3), pp Rogerson T and Chambers L, S COOL Students Cloud Observations On-line, NASA's LRC, Szalowski, K., The effect of the solar eclipse on air temperature and near the ground. Journal of atmospheric and solar-terrestrial physics, 64(15), pp Udina M., Soler M. R., Viana S., and Yague C., Model simulation of gravity waves triggered by a density current. Q. J. R. Meteorol. Soc. 139: Zeiler M, Total solar eclipse of August 21, 2017,

CPTEC and NCEP Model Forecast Drift and South America during the Southern Hemisphere Summer

CPTEC and NCEP Model Forecast Drift and South America during the Southern Hemisphere Summer José Antonio Aravéquia 1 Pedro L. Silva Dias 2 (1) Center for Weather Forecasting and Climate Research National