Search NASA⌕ Search

SEARCH · Search NASA

Results for “SEASONAL VARIATIONS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Diurnal and Seasonal Variations in Chlorophyll Fluorescence Associated with Photosynthesis at Leaf and Canopy Scales

There is a critical need for sensitive remote sensing approaches to monitor the parameters governing photosynthesis, at the temporal scales relevant to their natural dynamics. The photochemical reflectance index (PRI) and chlorophyll fluorescence (F) offer a strong potential for monitoring photosynthesis at local, regional, and global scales, however the relationships between photosynthesis and solar induced F (SIF) on diurnal and seasonal scales are not fully understood. This study examines how the fine spatial and temporal scale SIF observations relate to leaf level chlorophyll fluorescence metrics (i.e., PSII yield, YII and electron transport rate, ETR), canopy gross primary productivity (GPP), and PRI. The results contribute to enhancing the understanding of how SIF can be used to monitor canopy photosynthesis. This effort captured the seasonal and diurnal variation in GPP, reflectance, F, and SIF in the O2A (SIFA) and O2B (SIFB) atmospheric bands for corn (Zea mays L.) at a study site in Greenbelt, MD. Positive linear relationships of SIF to canopy GPP and to leaf ETR were documented, corroborating published reports. Our findings demonstrate that canopy SIF metrics are able to capture the dynamics in photosynthesis at both leaf and canopy levels, and show that the relationship between GPP and SIF metrics differs depending on the light conditions (i.e., above or below saturation level for photosynthesis). The sum of SIFA and SIFB (SIFA+B), as well as the SIFA+B yield, captured the dynamics in GPP and light use efficiency, suggesting the importance of including SIFB in monitoring photosynthetic function. Further efforts are required to determine if these findings will scale successfully to airborne and satellite levels, and to document the effects of data uncertainties on the scaling.

Campbell, Petya K.↗
NASA NTRS1972

Quasi-seasonal variation in the sun

The results of an investigation on the effects of earth seasonal changes on solar activity, particularly sunspots, are given. These results show corpuscular and electromagnetic activity increased during the equinoctial months. In addition the electromagnetic aspect tends to increase during the winter months. It was suggested that seasonal changes in sunspot numbers may be caused by the tidal forces and the processional torques exerted by the various planets in the solar atmosphere.

Chandra, S.↗
NASA NTRS2019

Titan's Neutral Atmosphere Seasonal Variations up to the End of the Cassini Mission

In this paper we report new results concerning the seasonal atmospheric evolution near Titan's poles and equator using the Cassini Composite Infrared Spectrometer (CIRS). In previous papers (Coustenis et al. 2016 and 2018), after the 2010 equinox, we have monitored Titan's stratosphere since the beginning of the mission and reported recently on the observed strong temperature decrease and compositional enhancement above Titan's southern polar latitudes since 2012 of several trace species such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect followed the transition of Titan's seasons from northern winter in 2002 to northern summer in 2017, while at that latter time, the southern hemisphere was entering winter. From 2013 until 2016, the northern polar region has shown a temperature increase of 10 K, while the south has shown a more significant decrease (up to 25 K) in a similar period of time. The stratosphere over the south pole of Titan shows a change in shape with a steeper positive slope and an increase in temperature in 2017 with respect to 2014, by 10-50 K in the 0.5 mbar-0.05 mbar pressure range, the larger 2017 temperatures observed in the higher atmospheric levels around 0.05 mbar, while in average the 70°S values return closer to the warmer ones found in 2012. While the south polar region is continuously enhanced since 2012, the chemical content in the north is showing a clear depletion for all molecules only since 2015 (Coustenis et al., 2018). We present here a complementary analysis of nadir spectra acquired by Cassini/CIRS at high resolution during the last year of the Cassini mission in 2017 and describe the temperature and composition variations near Titan's poles and at the equator over almost two Titan seasons. The 2017 data we have acquired and analyzed here are important because they are the only nadir ones afforded since 2014 close to the south pole at high resolution. They show no significant changes in the north with respect to 2016, but a large temperature increase in the southern polar stratosphere and a change in the temperature profiles shape while the South is also finally showing a related significant decrease in most of the abundances.

Coustenis, A.↗
NASA NTRS1985

Long-term (solar cycle) and seasonal variations of upflowing ionospheric ion events at DE 1 altitudes

In the investigation conducted by Yau et al. (1984), the occurrence frequency distribution of upflowing ionospheric ions (UFI) in the auroral and polar cap ionosphere up to 23,300 km altitude was determined using the Energetic Ion Composition Spectrometer (EICS) data acquired in the first orbital cycle (18 months) of Dynamics Explorer 1 (DE 1). The present paper is concerned with the seasonal and long-term variations in the occurrence and composition characteristics of upflowing ions. The observed solar cycle and seasonal dependences of upflowing ionospheric ion occurrence morphology are summarized schematically in a graph. It is found that the acceleration altitude of O(+) UFI is modulated by the atmospheric scale height, which increases with increasing solar activity (EUV flux). The O(+) UFI occurrence frequency (and hence O(+) outflow) increases at solar maximum.

Yau, A. W.↗
NASA NTRS2019

Titan's Neutral Atmosphere Seasonal Variations up to the End of the Cassini Mission

In this paper we report new results concerning the seasonal atmospheric evolution near Titan's poles and equator in terms of temperature and composition using nadir spectra acquired by the Cassini Composite Infrared Spectrometer (CIRS) at high spectral resolution during the last year of the Cassini mission in 2017 complementing previous investigations covering almost two Titan seasons. In recent previous papers (Coustenis et al., 2016, 2018), we have reported on monitoring of Titan's stratosphere near the poles after the mid-2009 northern spring equinox. In particular we have reported on the observed strong temperature decrease and compositional enhancement above Titan's southern polar latitudes since 2012 and until 2014 of several trace species, such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect accompanied the transition of Titan's seasons from northern winter in 2002 to northern summer in 2017, while at that latter time, the southern hemisphere was entering winter. Our new data, acquired in 2017 and analyzed here, are important because they are the only ones recorded since 2014 close to the south pole in the mid-infrared nadir mode at high resolution. A large temperature increase in the southern polar stratosphere (by 10–50 K in the 0.1 mbar–0.01 mbar pressure range) is found associated with a change in the temperature profile's shape. The 2017 observations also show a related significant decrease in most of the southern abundances which must have started sometime between 2014 and 2017. For the north, the spectra indicate a continuation of the decrease of the abundances which we first reported to have started in 2015 and small temperature variations. We discuss comparisons with other results and with current photochemical and dynamical models which could be updated and improved by the new constraints set by the findings presented here.

A Coustenis↗
NASA NTRS1996

Seasonal Variation of Mass Transport Across the Tropopause

The annual cycle of the net mass transport across the extratropical tropopause is examined. Contributions from both the global-scale meridional circulation and the mass variation of the lowermost stratosphere are included. For the northern hemisphere the mass of the lowermost stratosphere has a distinct annual cycle, whereas for the southern hemisphere, the corresponding variation is weak. The net mass transport across the tropopause in the northern hemisphere has a maximum in late spring and a distinct minimum in autumn. This variation and its magnitude compare well with older estimates based on representative Sr-90 mixing ratios. For the southern hemisphere the seasonal cycle of the net mass transport is weaker and follows roughly the annual variation of the net mass flux across a nearby isentropic surface.

Appenzeller, Christof↗
NASA NTRS1984

Seasonal variations of Pb-210 and Po-210 concentrations in an oligotrophic lake

In order to examine spatial and temporal variability during the seasonal cycle of the oligotrophic Crystal Lake, Wisconsin, vertical distribution measurements of Pb-210 and Po-210 in both the dissolved and particulate phases were conducted. Mass balance considerations indicate that the removal rates of the two isotopes from the water column to the sediment vary temporally by nearly an order of magnitude. The mean removal residence time was estimated to be 0.095 yr for Pb-210 and 0.26 yr for Po-210, suggesting a difference in the extent of water column recycling. Calculations indicate a cyclic response of the water column Po-210 inventory which corresponds to successive time periods when there were net losses or gains; this response may be due to rapid biological removal and subsequent release from the sediment of freshly deposited Po-210.

Talbot, R. W.↗
NASA NTRS1999

Angular and Seasonal Variation of Spectral Surface Reflectance Ratios: Implications for the Remote Sensing of Aerosol over Land

We obtain valuable information on the angular and seasonal variability of surface reflectance using a hand-held spectrometer from a light aircraft. The data is used to test a procedure that allows us to estimate visible surface reflectance from the longer wavelength 2.1 micrometer channel (mid-IR). Estimating or avoiding surface reflectance in the visible is a vital first step in most algorithms that retrieve aerosol optical thickness over land targets. The data indicate that specular reflection found when viewing targets from the forward direction can severely corrupt the relationships between the visible and 2.1 micrometer reflectance that were derived from nadir data. There is a month by month variation in the ratios between the visible and the mid-IR, weakly correlated to the Normalized Difference Vegetation Index (NDVI). If specular reflection is not avoided, the errors resulting from estimating surface reflectance from the mid-IR exceed the acceptable limit of DELTA-rho approximately 0.01 in roughly 40% of the cases, using the current algorithm. This is reduced to 25% of the cases if specular reflection is avoided. An alternative method that uses path radiance rather than explicitly estimating visible surface reflectance results in similar errors. The two methods have different strengths and weaknesses that require further study.

Remer, L. A.↗
NASA NTRS1986

Seasonal variations of troposheric ozone at Natal, Brazil

An analysis of ozone measurements from Natal, Brazil (6 deg S, 35 W), with a focus on the seasonal behavior in the troposphere, is presented. The amplitude of seasonal cycle at Natal is much larger than at Panama (9 deg N), the only other tropical site for which similar data are available. Concentrations of ozone in the middle troposphere in the southern spring are unexpectedly high, 60-70 ppb, similar to values found at northern midlatitudes in summer, and larger by 20-30 ppb than values found at Panama and at southern midlatitudes. It is suggested that photochemical production of ozone associated with emissions of CO, hydrocarbons, and NO(x) from biomass burning may contribute significantly to the high values of ozone, but note that stratospheric intrusions could also play a role. The data available at present do not permit a definitive evaluation of the relative importance of these two sources of ozone. The data from Natal, in combination with recent aircraft and surface data, show that tropical ozone exhibits strong spatial and temporal inhomogeneities. The distribution of tropospheric ozone appears to be considerably more complex than the traditional view, which suggested a northern midlatitude maximum and north/-south hemispheric asymmetry. The seasonal cycle in the total column of ozone at Natal appears to mirror the behavior of the tropospheric contribution to the ozone column rather than the stratospheric contribution, and this may account for differences in the annual cycle of the total column at Natal versus other tropical locations.

Logan, J. A.↗
NASA NTRS1994

Infrared spectroscopic measurements of the ethane (C2H6) total column abundance above Mauna Loa, Hawaii -- seasonal variations

About 200 i.r. solar spectra recorded at 0.01/cm resolution on 71 days between November 1991 and July 1993 at the Network for the Detection of Stratospheric Change (NDSC) station at Mauna Loa, Hawaii (latitude 19.53 deg N, longitude 155.58 deg W, elevation 3.459 km) have been analyzed with a nonlinear least-squares spectral fitting technique to study temporal variations in the total column of atmospheric ethane (C2H6) above the site. The results were derived from the analysis of the unresolved nu(sub 7) band (P)Q(sub 3) subbranch at 2976.8/cm. A distinct seasonal cycle is observed with a factor of 2 variation, a maximum total column of 1.16 x 10(exp 16) mol/sq cm at the end of winter, and a minimum total column of 0.53 x 10(exp 16) mol/sq cm at the end of summer. Our measurements are compared with previous observations and model predictions.

Rinsland, C. P.↗
NASA NTRS1994

Infrared Spectroscopic Measurements of the Ethane (C2H6) Total Column Abundance Above Mauna Loa, Hawaii: Seasonal Variations

About 200 i.r. solar spectra recorded at 0.01/ cm resolution on 71 days between November 1991 and July 1993 at the Network for the Detection of Stratospheric Change (NDSC) station at Mauna Loa, Hawaii (latitude 19.53 deg N, longitude 155.58 deg W, elevation 3.459 km) have been analyzed with a nonlinear least-squares spectral fitting technique to study temporal variations in the total column of atmospheric ethane (C2H6) above the site. The results were derived from the analysis of the unresolved nu(sub 7) band (sup P)Q(sub 3) subbranch at 2976.8/cm. A distinct seasonal cycle is observed with a factor of 2 variation, a maximum total column of 1.1 6 x 10(exp 16) mol /sq cm at the end of winter, and a minimum total column of 0.53 x 10(exp 16) mol/sq cm at the end of summer. Our measurements are compared with previous observations and model predictions.

Rinsland, C. P.↗
NASA NTRS2001

Seasonal variations of snow depth on Mars

Using topography collected over one martian year from the Mars Orbiter Laser Altimeter on the Mars Global Surveyor (MGS) spacecraft, we have measured temporal changes in the elevation of the martian surface that correlate with the seasonal cycle of carbon dioxide exchange between the surface and atmosphere. The greatest elevation change (1.5 to 2 meters) occurs at high latitudes ( above 80 degrees ), whereas the bulk of the mass exchange occurs at lower latitudes (below 75 degrees N and below 73 degrees S). An unexpected period of sublimation was observed during northern hemisphere autumn, coincident with dust storms in the southern hemisphere. Analysis of MGS Doppler tracking residuals revealed temporal variations in the flattening of Mars that correlate with elevation changes. The combined changes in gravity and elevation constrain the average density of seasonally deposited carbon dioxide to be 910 +/- 230 kilograms per cubic meter, which is considerably denser than terrestrial snow.

Carbon Dioxide↗
NASA NTRS1987

On seasonal variations of Mars' gravitational field

A great quantity of CO2 is exchanged between the Martian atmosphere and polar caps in the course of a Martian year. This exchange occurs in seasonal cycles: CO2 condenses to form the polar caps in winter and sublimes into the atmosphere in summer. The mass involved is about 25% of the total mass of the Martian atmosphere. This paper studies the effects of the CO2 mass redistribution on the Mars' gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO2 in the polar caps, and (2) the geographical distribution of gaseous CO2 in the atmosphere. The maximum changes produced by (1) in the low-degree zonal J sub l harmonics in the Mars gravitational field are found to be as much as 7.5 x 10 to the-9 power for J sub 2 (corresponding to 1.1 cm change in the geoid), and about half as much for J sub 3. The effect of (2) on some most prominent low-degree harmonics (for l =1-3) in the effective topography (defined as the departure of the true topography from the geoid) is also evaluated. Their magnitudes are large by Earth standards. Whether they can be observed by the upcoming Mars Observer is still uncertain.

Chao, B. Fong↗
NASA NTRS1995

Seasonal variation of atmospheric nitric acid over the South Pole in 1992

We conducted year-around measurements of mid infrared atmospheric emission over the South Pole in 1992. We were able to observe a large seasonal change of the total column of nitric acid (HNO3) vapor. During the summer the HNO3 column abundance was about 2 x 10(exp 16) molecules/sq cm. There was a small increase in the fall. A rapid decrease of 50% was observed in late June, soon after the stratospheric temperature reached the threshold for formation of type I polar stratospheric clouds (PSCs). By early July, the stratospheric temperature was cold enough to form type II PSCs, and the HNO3 column decreased to 7 x 10(exp 15) molecules/sq cm. Measured nitric acid values in the spring remained extremely low even after the stratosphere warmed well above PSC temperatures. This may indicate permanent removal of HNO3 by gravitational settling, or long-term sequestering in large particles. Normal summer values were not observed until the vortex dissipated and allowed the lateral transport of HNO3 to the south polar region.

Allen, Renate Van↗
NASA NTRS1989

Seasonal variations of volcanic eruption frequencies

Do volcanic eruptions have a tendency to occur more frequently in the months of May and June? Some past evidence suggests that they do. The present study, based on the new eruption catalog of Simkin et al.(1981), investigates the monthly statistics of the largest eruptions, grouped according to explosive magnitude, geographical latitude, and year. At the 2-delta level, no month-to-month variations in eruption frequency are found to be statistically significant. Examination of previously published month-to-month variations suggests that they, too, are not statistically significant. It is concluded that volcanism, at least averaged over large portions of the globe, is probably not periodic on a seasonal or annual time scale.

Stothers, Richard B.↗
NASA NTRS2014

Seasonal Variations in Mercury's Dayside Calcium Exosphere

The Mercury Atmospheric and Surface Composition Spectrometer on the MESSENGER spacecraft has observed calcium emission in Mercury's exosphere on a near-daily basis since March 2011. During MESSENGER's primary and first extended missions (March 2011 - March 2013) the dayside calcium exosphere was measured over eight Mercury years. We have simulated these data with a Monte Carlo model of exospheric source processes to show that (a) there is a persistent source of energetic calcium located in the dawn equatorial region, (b) there is a seasonal dependence in the calcium source rate, and (c) there are no obvious year-to-year variations in the near-surface dayside calcium exosphere. Although the precise mechanism responsible for ejecting the calcium has not yet been determined, the most likely process is the dissociation of Ca-bearing molecules produced in micrometeoroid impact plumes to form energetic, escaping calcium atoms.

Exosphere↗
NASA NTRS1998

Shallow Remineralization in the Sargasso Sea Estimated from Seasonal Variations in Oxygen and Dissolved Inorganic Carbon

A diagnostic model of the mean annual cycles of dissolved inorganic carbon (DIC) and oxygen below the mixed layer at the Bermuda Atlantic Time-series Study (BATS) site is presented and used to estimate organic carbon remineralization in the seasonal thermocline. The model includes lateral and vertical advection as well as vertical, diffusion. Very good agreement is found for the remineralization estimates based on oxygen and DIC. Net remineralization averaged from mid-spring to early fall is found to be a maximum between 120 and 140 in. Remineralization integrated between 100 (the compensation depth) and 250 m during this period is estimated to be about 1 mol C/sq m. This flux is consistent with independent estimates of the loss of particulate and dissolved organic carbon.

Ono, S.↗
NASA NTRS2012

Seasonal and Non-Seasonal Variations of Jupiter's Atmosphere from Observations of Thermal Emission, 1994-2011

We analyzed mid-infrared images of Jupiter's thermal emission, covering approx.1.5 Jovian years, acquired in discrete filters between 7.8 and 24.5 microns. The behavior of stratospheric (approx.10-mbar) and tropospheric (approx.100-400 mbar) temperatures is generally consistent with predictions of seasonal variability, with differences between 100-mbar temperatures +/-50-60deg from the equator on the order of +/-2. Removing this effect, there appear to be long-term quasi-periodic variability of tropospheric temperatures, whose amplitude, phase and period depend on latitude. The behavior of temperatures in the Equatorial Zone (EZ) suggests a approx.4-6-year period with amplitude of about +/-1-1.5 K in temperature. At mid-latitudes, the periodicity is more distinct with amplitudes around +/-1.5-2.5 K and 4-8 year periods. The 4.2-year variation of stratospheric temperatures known as the quasiquadrennial oscillation or "QQO" (Leovy et al. 1991, Nature 354, 380) continued during this period. There were no variations of zonal mean temperatures associated with any of the "global upheaval" events that have produced dramatic changes of jupiter's visible appearance and cloud cover, although there are colder discrete regions associated with updrafts, e.g. the early stages of the re-darkening ("revival") of the South Equatorial Belt (SEB) in late 2010. On the other hand increases in the visible albedos ("fades") of belts are accompanied by increases in the thickness of a 700-mbar cloud layer (most likely NH3 ice) and clouds at higher pressures, together with the mixing ratio of NH3 gas near 400 mbar (above its condensation level). These quantities decrease during re-darkening ("revival") episodes, during which we note discrete features that are exceptions to the general correlation between dark albedos and minimal cloudiness. In contrast to all these changes, the meridional distribution of the 240-mbar para-H2 fraction appears to be invariant in time.

Orton, G.↗