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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Estimates of the seasonal mean vertical velocity fields of the extratropical Northern Hemisphere

Indirect methods are employed to estimate the wintertime and summertime mean vertical velocity fields of the extratropical Northern Hemisphere and intercomparisons are made, together with comparisons with mean seasonal patterns of cloudiness and precipitation. Twice-daily NMC operational analyses produced general circulation statistics for 11 winters and 12 summers, permitting calculation of the seasonal NMC averages for 6 hr forecasts, solution of the omega equation, integration of continuity equation downward from 100 mb, and solution of the thermodynamic energy equation in the absence of diabatic heating. The methods all yielded similar vertical velocity patterns; however, the magnitude of the vertical velocities could not be calculated with great accuracy. Orography was concluded to have less of an effect in summer than in winter, when winds are stronger.

White, G. H.↗
NASA NTRS1980

Thundercloud electrification models in atmospheric electricity and meteorology

A survey is presented of presently-available theoretical models. The models are classified into three main groups: (1) convection models, (2) precipitation models, and (3) general models. The strengths and weaknesses of the models, their dimensionalities and degrees of sophistication, the nature of their inputs and outputs, and the various specific charging mechanisms treated by them, are considered. In results obtained to date, the convection models predict no significant electrification enhancement based on conductivity gradients and convection alone, with the assumed air circulation patterns. Results of the precipitation models show that the initial electrification can occur rapidly and stably through noninductive collision mechanisms involving ice, and breakdown-strength electric fields can relatively easily be achieved subsequently through the collisional-inductive mechanism. A critical difficulty of the collision mechanisms is imprecise knowledge of relaxation times versus contact times, which can easily lead to overestimates of electrification. The general model results tend to support those of the precipitation models in emphasizing the high potential effectiveness of the collisional-inductive mechanism.

Parker, L. W.↗
NASA NTRS2002

Global Precipitation Analyses at Monthly to 3-HR Time Scales

Global precipitation analysis covering the last few decades and the impact of the new TRMM precipitation observations are discussed. The 20+ year, monthly, globally complete precipitation analysis of the World Climate Research Program's (WCRP/GEWEX) Global Precipitation Climatology Project (GPCP) is used to explore global and regional variations and trends and is compared to the much shorter TRMM(Tropica1 Rainfall Measuring Mission) tropical data set. A trend pattern that is a combination of both El Nino and La Nina precipitation features is evident in the 20-year data set. This pattern is related to an increase with time in the number of combined months of El Nino and La Nina during the 20 year period. Monthly anomalies of precipitation are related to ENSO variations with clear signals extending into middle and high latitudes of both hemispheres. The GPCP daily, 1deg latitude-longitude analysis, which is available from January 1997 to the present is described and the evolution of precipitation patterns on this time scale related to El Nino and La Nina is described. Finally, a TRMM-based 3-hr analysis is described that uses TRMM to calibrate polar-orbit microwave observations from SSM/I and geosynchronous IR observations and merges the various calibrated observations into a final, 3-hr resolution map. This TRMM standard product will soon be available for the entire TRMM period (January 1998- present). A real-time version of this merged product is being produced and is available at 0.25deg latitude-longitude resolution over the latitude range from 50degN-50degS. Images from this data set can be seen at the U.S. TRMM web site (trmm.gsfc.nasa.gov). Examples will be shown, including its use in monitoring flood conditions and relating weather-scale events to climate variations.

Adler, Robert F.↗
NASA NTRS2013

The Precipitation Response Over the Continental United States to Cold Tropical Pacific Sea Surface Temperatures

The dominant pattern of annual mean SST variability in the Pacific (in its cold phase) produces pronounced precipitation deficits over the continental United States (U.S.) throughout the annual cycle. This study investigates the physical and dynamical processes through which the cold Pacific pattern affects the U.S. precipitation, particularly the causes for the peak dry impacts in fall, as well as the nature of the differences between the summer and fall responses. Results, based on observations and reanalyses, show that the peak precipitation deficit over the U.S. during fall is primarily due to reduced atmospheric moisture transport from the Gulf of Mexico into the central and eastern U.S., and secondarily due to a reduction in local evaporation from land-atmosphere feedback. The former is associated with a strong and systematic low-level northeasterly flow anomaly over the southeastern U.S. that counteracts the northwest branch of the climatological flow associated with the north Atlantic subtropical high. The above northeasterly anomaly is maintained by both diabatic heating anomalies in the nearby Intra-American Seas and diabatic cooling anomalies in the tropical Pacific. In contrast, the modest summertime precipitation deficit over the U.S. is mainly the result of local land-atmosphere feedback; the rather weak and disorganized atmospheric circulation anomalies over and to the south of the U.S. make little contribution. An evaluation of NSIPP-1 AGCM simulations shows it to be deficient in simulating the warm season tropical convection responses over the Intra-American Seas to the cold Pacific pattern and thereby the precipitation responses over the U.S., a problem that appears to be common to many AGCMs.

SST↗
NASA NTRS2003

Perspectives on Forced Predictability

This talk addresses the relationships between weather and El Nino/Southern Oscillation (ENSO) and various other low frequency atmospheric variations such as the Pacific/North American pattern. We focus, in particular, on the predictability of extreme wintertime precipitation events over the continental United States. We first examine fifty years of daily precipitation observations and quantify the leading patterns of winter weather variability. These weather systems, familiar to operational weather forecasters, account for many of the major flooding events on the west coast as well as the major winter snowstorms along the east coast. We next examine the statistics of these storm systems with a particular focus on the occurrence of extreme events. The leading weather systems show varying degrees of linkages to low frequency atmospheric variability. We show, for example, that on seasonal time scales the probability of occurrence of certain types of west coast storms is strongly enhanced by El Nino, while it is reduced during winters with an anomalous trough to the west of the dateline. ENSO also has a strong impact on storms that develop over the Gulf of Mexico and affect much of the eastern United States, with enhanced storminess during El Nino, and reduced storminess during La Nina conditions. We conclude with an example of how well current climate models are able to reproduce the basic linkages between weather and low frequency variability.

Schubert, S.↗
NASA NTRS2011

The Changing California Coast: The Effect of a Variable Water Budget on Coastal Vegetation Succession

The land-ocean interface along the central coast of California is one of the most diverse biogeographic regions of the state. This area is composed of a species-rich mosaic of coastal grassland, shrubland, and forest vegetation types. An acceleration of conifer encroachment into shrublands and shrub encroachment into grasslands along the coast has been recently documented. These vegetation changes are believed to be driven primarily by fire suppression and changing grazing patterns. Climatic variables such as precipitation, fog, cloud cover, temperature, slope, and elevation also play an important role in vegetation succession. Our study area is located along the central California coast, which is characterized by a precipitation gradient from the relatively wetter and cooler north to the drier and warmer south. Some studies indicate changing fog patterns along this coast, which may greatly impact vegetation. A decrease in water availability could slow succession processes. The primary objective of this project is to determine if vegetation succession rates are changing for the study area and to identify climate and ecosystem variables which contribute to succession, specifically the transition among grassland, shrubland, and forest. To identify vegetation types and rates of succession, we classified two Landsat TM 5 scenes from 1985 to 2010 with a resulting overall accuracy of 82.4%. Vegetation succession was correlated to changes in maximum and minimum temperatures, precipitation, and elevation for each sub-region of the study area. Fog frequency was then compared between the northern and southern regions of the study area for determining the spatial relation between fog frequency and the percent of vegetation change.

Hsu, Wei-Chen↗
NASA NTRS1987

Determine precipitation rates from visible and infrared satellite images of clouds by pattern recognition technique

A more advanced cloud pattern analysis algorithm was subsequently developed to take the shape and brightness of the various clouds into account in a manner that is more consistent with the human analyst's perception of GOES cloud imagery. The results of that classification scheme were compared with precipitation probabilities observed from ships of opportunity off the U.S. east coast to derive empirical regressions between cloud types and precipitation probability. The cloud morphology was then quantitatively and objectively used to map precipitation probabilities during two winter months during which severe cold air outbreaks were observed over the northwest Atlantic. Precipitation probabilities associated with various cloud types are summarized. Maps of precipitation probability derived from the cloud morphology analysis program for two months and the precipitation probability derived from thirty years of ship observation were observed.

Weinman, James A.↗
NASA NTRS1987

Birkeland currents - Recent contributions from satellite magnetic field measurements

The important role that field-aligned Birkeland currents play in solar terrestrial coupling processes has been known from satellite observations for twenty years. Many satellite have been launched since the last Solar-Terrestrial Symposium with instruments capable of investigating the characteristics of Birkeland currents and their relationship to visible and UV auroral forms, particle precipitation, and convection flow patterns. An important result that has emerged is the close relationship between large-scale Birkeland currents and the orientation of the interplanetary magnetic field. These observations emphasize the fact that Birkeland currents are involved in a wide range of space plasma processes which range from small-scale ionospheric instabilities and irregularities to global scale energy coupling processes between the magnetosphere and solar wind.

Potemra, T. A.↗
NASA NTRS1991

The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program is to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative, manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, our immediate emphasis is on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we have developed unique global models that allow us to study the coupling between the different regions. These results are highlighted. Another important aspect of our NASA Theory Program concerns the effect that localized structure has on the macroscopic flow in the ionosphere, plasmasphere, thermosphere and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkeland current patterns) or time variations in these inputs due to storms and substorms. Also, some of the plasma flows that we predict with our macroscopic models may be unstable. Another one of our goals is to examine the stability of our predicted flows. Because time-dependent three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another long-range goal of our NASA Theory Program is to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This may involve a detailed comparison of kinetic, semikinetic, and hydrodynamic predictions for a given polar wind scenario or it may involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations will provide insight into when the various models can be used with confidence.

Schunk, Robert W.↗
NASA NTRS1990

The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program was to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, with the funding from this NASA program, we concentrated on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we developed unique global models that allowed us to study the coupling between the different regions. These results are highlighted in the next section. Another important aspect of our NASA Theory Program concerned the effect that localized 'structure' had on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkland current patterns) or time variations in these input due to storms and substorms. Also, some of the plasma flows that we predicted with our macroscopic models could be unstable, and another one of our goals was to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another goal of our NASA Theory Program was to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This could involve a detailed comparison of kinetic, semi-kinetic, and hydrodynamic predictions for a given polar wind scenario or it could involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations provides insight into when the various models can be used with confidence.

Schunk, Robert W.↗
NASA NTRS1992

The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program is to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, our immediate emphasis is on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we have developed unique global models that allow us to study the coupling between the different regions. Another important aspect of our NASA Theory Program concerns the effect that localized structure has on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkeland current patterns) or time variations in these inputs due to storms and substorms. Also, some of the plasma flows that we predict with our macroscopic models may be unstable, and another one of our goals is to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulation). Therefore, another long-range goal of our NASA Theory Program is to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This may involve a detailed comparison of kinetic, semikinetic, and hydrodynamic predictions for a given polar wind scenario or it may involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations will provide insight into when the various models can be used with confidence.

Schunk, R. W.↗
NASA NTRS1999

Regional Climate Simulation with a Variable Resolution Stretched Grid GCM: The Regional Down-Scaling Effects

The results obtained with the variable resolution stretched grid (SG) GEOS GCM (Goddard Earth Observing System General Circulation Models) are discussed, with the emphasis on the regional down-scaling effects and their dependence on the stretched grid design and parameters. A variable resolution SG-GCM and SG-DAS using a global stretched grid with fine resolution over an area of interest, is a viable new approach to REGIONAL and subregional CLIMATE studies and applications. The stretched grid approach is an ideal tool for representing regional to global scale interactions. It is an alternative to the widely used nested grid approach introduced a decade ago as a pioneering step in regional climate modeling. The GEOS SG-GCM is used for simulations of the anomalous U.S. climate events of 1988 drought and 1993 flood, with enhanced regional resolution. The height low level jet, precipitation and other diagnostic patterns are successfully simulated and show the efficient down-scaling over the area of interest the U.S. An imitation of the nested grid approach is performed using the developed SG-DAS (Data Assimilation System) that incorporates the SG-GCM. The SG-DAS is run with withholding data over the area of interest. The design immitates the nested grid framework with boundary conditions provided from analyses. No boundary condition buffer is needed for the case due to the global domain of integration used for the SG-GCM and SG-DAS. The experiments based on the newly developed versions of the GEOS SG-GCM and SG-DAS, with finer 0.5 degree (and higher) regional resolution, are briefly discussed. The major aspects of parallelization of the SG-GCM code are outlined. The KEY OBJECTIVES of the study are: 1) obtaining an efficient DOWN-SCALING over the area of interest with fine and very fine resolution; 2) providing CONSISTENT interactions between regional and global scales including the consistent representation of regional ENERGY and WATER BALANCES; 3) providing a high computational efficiency for future SG-GCM and SG-DAS versions using PARALLEL codes.

Fox-Rabinovitz, Michael S.↗
NASA NTRS2003

A Model Study of the Impact of Magnetic Field Reversal on Atmospheric Composition during Solar Proton Events

During a polarity transition of the Earth's magnetic field, the structure and strength of the field change significantly from their present values. This will alter the global pattern of charged particle precipitation into the atmosphere. Thus, particle precipitation is possible into regions that are at the moment effectively shielded by the Earth's magnetic field. A two-dimensional global fbHy coupled chemistry, radiation, and transport model of the atmosphere has been used to investigate how the increased particle precipitation affects the chemical composition of the middle and lower atmosphere. Ozone losses resulting from large energetic particle events are found to increase significantly, with resultant losses similar to those observed m the Antarctic ozone hole of the 1990s. This results in significant increases in surface UV-B radiation as well as changes in stratospheric temperature and circulation over a period of several months after large particle events.

Sinnhuber, Miaiam↗
NASA NTRS2005

The Flow of Plasma in the Solar-Terrestrial Environment

The overall goal of our NASA theory research is to trace the flow of mass, momentum, and energy through the magnetosphere-ionosphere-atmosphere system taking into account the coupling, time delays, and feedback mechanisms that are characteristic of the system. Our approach is to model the magnetosphere-ionosphere-atmosphere (M-I-A) system in a self-consistent quantitative manner using unique global models that allow us to study the coupling between the different regions on a range of spatial and temporal scales. The uniqueness of our global models stems from their high spatial and temporal resolutions, the physical processes included, and the numerical techniques employed. Currently, we have time-dependent global models of the ionosphere, thermosphere, polar wind, plasmasphere, and electrodynamics. It is now becoming clear that a significant fraction of the flow of mass, momentum, and energy in the M-I-A system occurs on relatively small spatial scales. Therefore, an important aspect of our NASA Theory program concerns the effect that mesoscale (100-l000 km) density structures have on the macroscopic flows in the ionosphere, thermosphere, and polar wind. The structures can be created either by structured magnetospheric inputs (i.e., structured electric field, precipitation, or Birkeland current patterns) or by time variations of these inputs due to geomagnetic storms and substorms. Some of the mesoscale structures of interest include sun-aligned polar cap arcs, propagating plasma patches, traveling convection vortices, subauroral ion drift (SAID) channels, gravity waves, and the polar hole.

Schunk, Robert W.↗
NASA NTRS2022

Accelerating Ice Loss From Peripheral Glaciers in North Greenland

In recent decades, Greenland's peripheral glaciers have experienced large-scale mass loss, resulting in a substantial contribution to sea level rise. While their total area of Greenland ice cover is relatively small (4%), their mass loss is disproportionally large compared to the Greenland ice sheet. Satellite altimetry from Ice, Cloud, and land Elevation Satellite (ICESat) and ICESat-2 shows that mass loss from Greenland's peripheral glaciers increased from 27.2 ± 6.2 Gt/yr (February 2003–October 2009) to 42.3 ± 6.2 Gt/yr (October 2018–December 2021). These relatively small glaciers now constitute 11 ± 2% of Greenland's ice loss and contribute to global sea level rise. In the period October 2018–December 2021, mass loss increased by a factor of four for peripheral glaciers in North Greenland. While peripheral glacier mass loss is widespread, we also observe a complex regional pattern where increases in precipitation at high altitudes have partially counteracted increases in melt at low altitude.

Greenland↗
NASA NTRS2012

Propagation of Convective Complexes Observed by TRMM in the Eastern Tropical Atlantic

Precipitation maxima during the West African summer monsoon propagate generally westward in tandem with African easterly waves. A heretofore unreported, repeating pattern of northward drift of precipitation maxima is detected on Tropical Rainfall Measurement Mission (TRMM satellite) time-latitude distributions of daily accumulations over the eastern tropical Atlantic. Corresponding 3-hourly TRMM accumulations show that the northward drifting envelopes of precipitation during August 2006 are often comprised of individual swaths propagating towards the southwest, presumably as mesoscale squall lines. The implied northward drift on the time-latitude distribution is a component of a resultant northwestward movement. The study examines the entire available record of TRMM precipitation observations, 1998-2010, to summarize TRMM maxima propagation over the eastern tropical Atlantic. Meridional displacements of precipitation maxima are most prevalent in June-September 2006, occurring less frequently during other summers. An investigation of geopotential and circulation fields, limited to two case studies, suggests mechanisms to explain some of the observed propagation of TRMM maxima. In one event, northward drift of the precipitation envelope is consistent with the corresponding displacement of the intertropical convergence zone trough, although the southwest propagation of individual mesoscale convection maxima does not correspond to any synoptic feature on reanalysis circulation or reanalysis downscaled by a regional model. One speculation is that southwestward propagation of precipitation maxima could be caused by regeneration of convection at outflow boundaries of mature thunderstorms.

Druyan, Leonard M.↗
NASA NTRS2021

Climate model projections from the Scenario Model Intercomparison Project (ScenarioMIP) of CMIP6

The Scenario Model Intercomparison Project (ScenarioMIP) defines and coordinates the main set of future climate projections, based on concentration-driven simulations, within the Coupled Model Intercomparison Project phase 6 (CMIP6). This paper presents a range of its outcomes by synthesizing results from the participating global coupled Earth system models. We limit our scope to the analysis of strictly geophysical outcomes: mainly global averages and spatial patterns of change for surface air temperature and precipitation. We also compare CMIP6 projections to CMIP5 results, especially for those scenarios that were designed to provide continuity across the CMIP phases, at the same time highlighting important differences in forcing composition, as well as in results. The range of future temperature and precipitation changes by the end of the century (2081–2100) encompassing the Tier 1 experiments based on the Shared Socioeconomic Pathway (SSP) scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) and SSP1-1.9 spans a larger range of outcomes compared to CMIP5, due to higher warming (by close to 1.5 °C) reached at the upper end of the 5 %–95 % envelope of the highest scenario (SSP5-8.5). This is due to both the wider range of radiative forcing that the new scenarios cover and the higher climate sensitivities in some of the new models compared to their CMIP5 predecessors. Spatial patterns of change for temperature and precipitation averaged over models and scenarios have familiar features, and an analysis of their variations confirms model structural differences to be the dominant source of uncertainty. Models also differ with respect to the size and evolution of internal variability as measured by individual models' initial condition ensemble spreads, according to a set of initial condition ensemble simulations available under SSP3-7.0. These experiments suggest a tendency for internal variability to decrease along the course of the century in this scenario, a result that will benefit from further analysis over a larger set of models. Benefits of mitigation, all else being equal in terms of societal drivers, appear clearly when comparing scenarios developed under the same SSP but to which different degrees of mitigation have been applied. It is also found that a mild overshoot in temperature of a few decades around mid-century, as represented in SSP5-3.4OS, does not affect the end outcome of temperature and precipitation changes by 2100, which return to the same levels as those reached by the gradually increasing SSP4-3.4 (not erasing the possibility, however, that other aspects of the system may not be as easily reversible). Central estimates of the time at which the ensemble means of the different scenarios reach a given warming level might be biased by the inclusion of models that have shown faster warming in the historical period than the observed. Those estimates show all scenarios reaching 1.5 °C of warming compared to the 1850–1900 baseline in the second half of the current decade, with the time span between slow and fast warming covering between 20 and 27 years from present. The warming level of 2 °C of warming is reached as early as 2039 by the ensemble mean under SSP5-8.5 but as late as the mid-2060s under SSP1-2.6. The highest warming level considered (5 °C) is reached by the ensemble mean only under SSP5-8.5 and not until the mid-2090s.d-2090s.

Scenario Model Intercomparison Project (ScenarioMI↗