Significant Diurnal Cycle Research Articles

Occurrence of upslope flows at the Pico mountaintop observatory: A case study of orographic flows on a small, volcanic island

Upslope flows caused by mechanical forcing in strong synoptic winds or by buoyant forcing driven by solar heating under weak synoptic winds can influence the air composition at mountaintop observatories. Using meteorological and trace gas measurements at the PICO‐NARE observatory on Pico mountain (Azores Islands, North Atlantic Ocean), the frequency and impact of such orographic flows on a small, volcanic, subtropical island was examined. To determine the origin of mechanically lifted air, upstream kinetic energy was balanced against potential energy gained during uplift (Sheppard's model). Mechanically forced upslope flow is most important during October through April, when the calculated probability of observing marine boundary layer (MBL) air at the observatory near the summit ranges from 35 to 60% per month. In contrast, lower synoptic wind speeds and a more stable lower free troposphere during May–September result in a reduced frequency of MBL impacts (<20%). Buoyant upslope flows (BUF) were quantified through meteorological measurements on the mountain slope in summer 2004. Diurnal cycles of wind direction on the mountain slope consistent with daytime upslope and nighttime downslope flow were found on 24% of the days during late June, July, and August 2004. Buoyant forcing can also occur in the presence of moderate synoptic winds, resulting in enhancement of the mechanically forced upslope flow on the windward side of the mountain. Such conditions were found on 15% of the summer days in 2004. However, on BUF days the specific humidity at the mountaintop was significantly smaller than on the slope, indicating turbulent mixing during ascent or vertical decoupling of air masses. Impacts of BUF or a mixture of buoyant and mechanical upslope flow on O3 or nitrogen oxides mixing ratios at the mountaintop station were rare or extremely small, and no significant diurnal cycle of O3 (expected if daytime BUF of MBL air occurred regularly) was present. Midday increases in isoprene concentrations, a nonmethane hydrocarbon (NMHC) expected to be emitted from vegetation more than 700 m below the PICO‐NARE station, were found on 54% of the days during May–August 2005. No corresponding increase in n‐butane (used for heating and cooking at sea level residences) was detected, suggesting that the air did not originate from as low as sea level. These results indicate that the latitude, size, and topography of Pico island combine to prevent frequent transport of MBL air to the PICO‐NARE station in the summer.

The Northwestern Argentinean Low: A Study of Two Typical Events

Abstract A low pressure system [known as the northwestern Argentinean low (NAL)] is commonly observed over northwestern Argentina near the Andean slopes. This study describes two NAL episodes for summer and winter, with emphasis on the characterization of their three-dimensional structure and temporal variability. With the aid of a high-resolution regional model [Eta/Centro de Previsao de Tempo e Estudos Climaticos (CPTEC)], the main mechanisms involved in the NAL life cycle were studied in order to examine how the thermal topographical processes influenced the system behavior. Surface pressure changes in the NAL are mostly dominated by the 600–900-hPa thickness variability, suggesting its thermal character. Based on this result, the temperature tendency equation has been used to quantify all the contributions to thermal changes. The summer NAL has a significant diurnal cycle that has been dominated by surface warming. This single mechanism can explain the low pressure system formation by itself, suggesti...

Climate dynamics along the arid northern coast of Chile: The 1997–1998 Dinámica del Clima de la Región de Antofagasta (DICLIMA) experiment

The DICLIMA field experiment was designed to test and quantify the hypothesis of an afternoon enhancement of the coastal subsidence in the extremely arid northern Chile because of solar heating over the west slope of the Andes. Ten‐day campaigns near Antofagasta (23°S) were carried out in January 1997, July 1997, and January 1998. Significant diurnal cycles in temperature, mixing ratio, and wind from about 1000 to 4000 m above sea level were observed. This layer was decoupled from the marine boundary layer circulation below by the subsidence inversion when its base was under the average height of the coastal mountain range. The solar heating cycle over the Andes and associated circulation resulted in a mean afternoon zonal divergence above the subsidence inversion base of about 30 × 10−6 s−1, exceeding by a factor of 5 typical subtropical west coast divergences. The corresponding early morning convergence was particularly intense during the austral winter experiment. In spite of the very strong El Niño conditions that prevailed during the July 1997 and January 1998 experiments, the overwhelming control that radiation exerts on the daily cycles of the atmospheric circulation over the west slope of the Andes seems to guarantee the general validity of the results.

Gaseous Elemental Mercury in the Marine Boundary Layer: Evidence for Rapid Removal in Anthropogenic Pollution

In this study, gas-phase elemental mercury (Hg0) and related species (including inorganic reactive gaseous mercury (RGM) and particulate mercury (PHg)) were measured at Cheeka Peak Observatory (CPO), Washington State, in the marine boundary layer during 2001-2002. Air of continental origin containing anthropogenic pollutants from the urban areas to the east contained on average 5.3% lower Hg0 levels as compared to the marine background. This result is difficult to reconcile since it is known that industrial emissions in our region are sources of Hg0. The rate of removal of Hg0 from a pollution plume necessary to account for our observations is inconsistent with the accepted view of Hg0 as a stable atmospheric pollutant. The largest and most frequent Hg0 loss events occurred in the presence of increased ozone (O3) during the summer. Hg0 and O3 also display diurnal cycles that are out-of-phase with one another. In other seasons Hg0 behavior is less consistent, as we observe weak positive correlations with O3 and occasional Hg0 enhancements in local pollution. RGM and PHg concentrations are enhanced only slightly during Hg0 loss events, comprising a small fraction of the mercury pool (approximately 3%). Long-range transported pollution of Asian origin was also detected at CPO, and this contains both higher and lower levels of Hg0 as compared to the background with maximum changes being <20%. Here, the more photochemically processed the air mass, as determined by propane/ethane ratios, the more likely we are to observe Hg0 loss. Air from the marine background in summer displays a significant diurnal cycle with a phase that matches the diurnal cycles seen in polluted air masses. A Junge lifetime for Hg0 in the clean marine boundary layer is calculated to be 7.1 months, which is on the low end of previous estimates (0.5-2 yr).

Rapid changes in ozone mixing ratios at Cerro Tololo (30°10′S, 70°48′W, 2200 m) in connection with cutoff lows and deep troughs

Rapid changes in surface ozone mixing ratios (up to 15 ppbv over 12 hours) at the Cerro Tololo (CT) station (70°W, 30°S, 2200 m) over the period 1996–2000 are analyzed. These changes explain most of the wintertime variability of the ozone data at CT. Since the wintertime data show no significant diurnal cycle, local circulations and in situ photochemical processes cannot account for the sudden changes in ozone. Rather, a synoptic‐scale forcing of the changes is described on the basis of composite analyses of reanalysis data. Synoptic configurations associated with sudden changes in ozone were separated into W and D cases, according to the local evolution of humidity. W cases are characterized by humidity values in excess of 4 hPa lasting one or two days before the ozone maximum. D cases show no significant change in humidity before the ozone maximum. Both in W and in D cases, stratospheric air appears to be advected from polar latitudes to midlatitudes and subtropical latitudes during the development of cutoff lows and deep troughs. The origin of the air arriving at CT during a W and a D case study was assessed using mesoscale numerical simulations. The model calculations for the W case show a deep stratospheric intrusion reaching the lower troposphere in subtropical latitudes during the amplification and mature stages of a cutoff low. For D cases the stratospheric intrusion is mostly confined to midlatitudes and to an oceanic area far from the site of study. Analyses of trajectories show that in both cases, high ozone mixing ratios at the surface occur in connection with air parcels having a stratospheric history.

Diurnal cycles and seasonal variation of isoprene and its oxidation products in the tropical savanna atmosphere

[1] Using the proton transfer reaction mass spectrometry (PTR-MS) technique, isoprene and its oxidation products were measured in a productive woodland savanna (Calabozo site, during the wet and dry seasons) and a less productive grassland savanna (La Gran Sabana, Parupa site). The measured protonated masses in the PTR-MS, postulated compounds, and daytime average volume mixing ratios at the Calabozo site during the wet season are: 69 isoprene (1.62 nmol/mol), 71 methyl vinyl ketone + methacrolein (0.98 nmol/mol), 83 3-methyl furan + unsaturated C5-hydroxycarbonyls (0.12 nmol/mol), and 101 isoprene hydroperoxides (0.16 nmol/mol). Significant diurnal cycles of the hydrocarbon concentrations were observed, with distinct characteristics between sites and seasons. Two times lower levels of isoprene were observed during the dry season. At the Parupa site measured concentrations of all masses were about three times lower than at the Calabozo site during the wet season, and significant transport of isoprene from upwind forests was observed. Comparison with a photochemical box model revealed that surface deposition is likely a significant sink for isoprene and its oxidation products. An isoprene source of 2.1–3.2 × 106 molec/cm3/s and an HO concentration of 4.1–6.0 × 105 molec/cm3 averaged over 24 hours were needed to match the observed mixing ratios. Assuming a mixed boundary layer of 1500 m and an isoprene source half the strength during the 5 months dry season, a global emission of isoprene to the atmosphere from tropical savannas between 53 and 79 Tg C/yr can be calculated from our results if the Calabozo site is representative.

Pumpkins and onions and balloon design

The reach for a capability to make long flights (months) with heavy payloads (tonnes) has long been pursued. The closest we have come is with polar flights devoid of a significant diurnal cycle. Superpressure technology, with its ability to survive diurnal cycles, is an obvious choice, but materials limitations have been an obstacle to realizing these ambitious goals. Now comes an assortment of new synthetic materials, coupled with a special variety of superpressure balloon which, in combination, is poised to yield a solution for our enhanced duration/payload quest. In this paper we are looking not at materials, but only at a balloon concept. This concept is a “natural shape” oblate spheroid balloon whose shape is chosen to exploit properties of component materials, particularly newly available ones. The current variation of this concept is called a “pumpkin” balloon. The most visible work on this shape is that done by France's CNES, Japan's ISAS, and in the USA by NASA's Wallops Flight Facility. But the basic design idea is not new; it extends back at least a half century. This paper traces the origins of the shape, its evolution through various iterations, and it speculates on some of the recent thinking regarding construction details.

Effect of Pineal Extirpation on Daily and Long-Term Variations in Thermal Tolerance in a Tropical Catfish, Clarias batrachus

Thermal tolerance in laboratory acclimated Clarias batrachus was assessed by determining the critical thermal maximum (CTM) every 4 hours for 2 days in intact and pinealectomized (Px) animals during January and in sham-pinealectomized (sham-Px) and Px animals during April. In the intact and sham-Px group a statistically significant (P <0.005) diurnal cycle of thermal tolerance was validated which was asynchronous with that of the daily fluctuations in ambient temperature (Ta). A nocturnal elevation of thermal tolerance was observed in all the groups. Pineal removal resulted in a highly significant (P <0.001) increase of CTM. Additionally, pinealectomy abolished the normal diurnal cycle in CTM or dampened its amplitude considerably. In another experiment the long-term effect of pinealectomy on thermal tolerance was determined in sham-Px and Px fishes. CTM was significantly (P <0.05) elevated during the first three weeks following pinealectomy, pointing to a short-term control from the pineal on thermal tolerance. This study provides the first demonstration of a direct pineal influence on thermal tolerance and its temporal organization.

The Low-Level Structure and Evolution of a Dry Arctic Front over the Central United States. Part I: Mesoscale Observations

Abstract Observations taken over the period 8–10 March 1992 during the Storm-scale Operational and Research Meteorology Fronts Experiment Systems Test in the central United States are used to document the detailed low-level structure and evolution of a shallow, dry arctic front. The front was characterized by cloudy skies to its north side and clear skies to its south side. It was essentially two-dimensional in the zone of intense observations. There was a significant diurnal cycle in the magnitude of the potential temperature gradient across both the subsynoptic and mesoscale frontal zones, but imposed upon an underlying, more gradual, increase over the three days. On the warm (cloudless) side., the temperature increased and decreased in response to the diurnal heating cycle, while on the cold (cloudy) side the shape of the temperature decrease from its warm-side value (first dropping rapidly and then slowly in an exponential-like manner) remained fairly steady. The authors attribute the strong diurnal v...

Diurnal variation in oxygen consumption by molting and nonmolting sparrows

Abstract To evaluate the effects of time of measurement on estimates of daily energetic costs of avian molt, oxygen (O 2 ) consumption was measured for molting and wintering sparrows ( Zonotrichia leucophrys gambelii ) at 6-hr intervals through the 24-hr cycle and continuously overnight for wintering sparrows exposed to long nights (9L:15D, 23°C). A significant diurnal cycle in O 2 consumption was evident in all birds. In molting birds (16L:8D, 23°C), O 2 consumption during midday was significantly higher than at all other times, and O 2 consumption towards the end of the night was higher than at its beginning. O 2 consumption by wintering birds was significantly higher towards the end of the night than during midnight and was typically higher towards the end of the night than during midday, though not always significantly so. Overnight, O 2 consumption by wintering birds (9L:15D) initially decreased, then remained stable, and finally increased towards the end of the night. Daily O 2 consumption was higher for molting birds than for wintering birds, but the increase in metabolism of molting birds compared with that of wintering birds varied through the diurnal cycle. Based on daily measures of O 2 consumption, peak energetic costs of molt in sparrows were estimated as 10.0 to 19.1 kJ/d.

Principal Modes of Variation of Rain-Rate Probability Distributions

Abstract Radar or satellite observations of an area generate sequences of rain-rate maps. From a gridded map a histogram of rain rates can be obtained representing the relative areas occupied by rain rates of various strengths. The histograms vary with time as precipitating systems in the area evolve and decay and amounts of convective and stratiform rain in the area change. A method of decomposing the histograms into linear combinations of a few empirical distributions with time-dependent coefficients is developed, using principal component analysis as a starting point. When applied to a tropical Atlantic dataset (GATE), two distributions emerge naturally from the analysis, resembling stratiform and convective rain-rate distributions in that they peak at low and high rain rates, respectively. The two “modes” have different timescales and only the high-rain-rate mode has a statistically significant diurnal cycle. The ability of just two modes to describe rain variability over an area can explain why metho...

Measurements of light atmospheric hydrocarbons over the Atlantic in regions of low biological activity

More than 200 in situ measurements of several selected nonmethane hydrocarbons (NMHCs) were made in the remote marine atmosphere over the Atlantic between 40°S and 50°N. Ethane, the by far longest lived of the NMHCs, showed southern hemispheric mixing ratios around 280 ppt, comparable in magnitude to most other previous measurements. The mixing ratios of ethene, propene, propane, and i‐ and n‐butane in the southern hemisphere were in the range of 10–30 ppt. For i‐pentane and n‐pentane the atmospheric mixing ratios in the southern hemisphere were below the detection limit of 15–20 ppt. These values are rather low compared to other published measurements in the marine atmosphere. This is due to the remoteness of the measuring locations and the very low biological activity in the surrounding ocean areas. For all alkanes the latitudinal profiles exhibit a considerable decrease from north to south. The relative hydrocarbon patterns show that the alkanes in the northern hemisphere are primarily due to long‐range transport from continental or coastal areas. In general the transport times exceed several days. Consequently, the observed northern hemispheric ethene and propene mixing ratios must be, with few exceptions, primarily the result of oceanic emissions. The average difference of these compounds by a factor of 2 between the southern and the northern hemisphere can be explained by change of the phytoplankton concentration in ocean water. There is little or no indication for the existence of significant diurnal cycles for these two alkenes.

Ozone in the marine boundary layer over the Pacific and Indian Oceans: Latitudinal gradients and diurnal cycles

Ozone concentrations in the atmospheric boundary layer of the Pacific and Indian Oceans were measured on four separate oceanographic research cruises (July 1986, May to August 1987, April to May 1988). These measurements show a distinct zone of near zero (≤3 ppb) ozone concentration in the central equatorial Pacific in April–May, with ozone increasing in this region over the next 4 months. The seasonal observed change in the latitudinal gradient of ozone is consistent with previous ozone measurements at Hilo and Samoa by Oltmans and Komhyr [1986] and predictions from an atmospheric general circulation model study [Levy et al., 1985]. A significant diurnal cycle of ozone was found in almost all locations with a maximum near sunrise, a minimum in the late afternoon, and a peak‐to‐peak amplitude of 1 to 2 ppb (10–20%), similar to that predicted by a photochemical model in the low NOx limit [Thompson and Lenschow, 1984].

Barrow surface aerosol: 1976–1986

Measurements at Barrow during the first Arctic Gas and Aerosol Sampling Program (AGASP-I), conducted in March–April 1983, showed a series of aerosol events detected at the ground that coincided with rapid long-range transport paths from Eurasia to the vicinity of Barrow. These events were strongly correlated with aerosol loading in the vertical column (optical depth). Aerosol and meteorological measurements at Barrow during the second AGASP (AGASP-II), conducted in April 1986, indicate no rapid long-range transport from lower-latitude source regions to the vicinity of Barrow, and only limited vertical transport from above the boundary layer to the surface. Aerosol size distribution measurements in the 0.005–0.1 μm diameter size range using a Nuclepore-filter diffusion battery apparatus showed a median diameter of about 0.01 μm during times of high condensation nucleus (CN) concentrations and 0.05 μm during low concentrations. Aerosol black carbon concentrations exceeding 200 ng m −3 were detected at the surface and were more strongly correlated with CN concentrations than with aerosol scattering extinction ( σ sp ), suggesting that aerosol carbon was generally associated with small particles rather than large particles. A continuous record of CN and σ sp measurements is available from 1976 to the present. The σ sp data show a strong annual cycle, having a maximum exceeding 10 −5 m −1 in the winter and spring (the Arctic haze), and a minimum of about 10 −6m −1 in the summer and fall. The CN data show a semiannual cycle, having a maximum of several hundred per cubic centimeter coinciding with the maximum in σ sp in early spring, and a secondary maximum in August. Minima in CN concentration of about 100 cm −3 occur in summer and late fall. No significant diurnal cycle appears in either the CN or σ sp long-term records.

Variability of net longwave radiation over the eastern North Pacific Ocean

The net longwave radiation at the sea surface (LW↑↓) was measured over the eastern North Pacific Ocean for 22 days during the fall of 1982. These measurements were made from the R/P FLIP as part of the Optical Dynamics Experiment. The mean LW↑↓ emitted from the sea surface was 52.0 W/m2 with a variance of 802.6 W2/m4. The largest fraction of the variance was observed to be in the diurnal frequency band. LW↑↓ and the total cloud amount exhibited significant diurnal cycles (amplitudes of 13.5 W/m2 and 7%, respectively) which were negatively correlated. LW↑↓ measurements were compared with values obtained from seven different bulk formulas for LW↑↓ in order to evaluate their predictive capabilities. These formulas predict less than 45% of LW↑↓ variance, indicating that these methods are inadequate for the description of LW↑↓ variability. Statistical predictions were made using linear hindcastors to examine the relationships between LW↑↓ and other surface meteorological and oceanographic parameters. The signs and magnitudes of the arbitrary coefficients in the linear hindcastors are consistent with hypotheses used for a conceptual model of radiant heat transfer between two parallel gray plates through an interacting medium. The highest predictive skill levels (54.3–55.3% of the variance explained) occur for the case of a two component linear hindcastor where both the cloud layer and the water vapor concentration above the sea surface are taken into account. The success of the statistical predictions indicates that the fundamental physics relevant to LW↑↓ variability are incorporated in the conceptual parallel plate model.

Diurnal, shade, and hybrid effects on nitrate content of young corn stalks

Abstract Significant correlations have been found between the nitrate concentration in young corn (Zea mays L.) stalks and available soi 1 N and relative grain yield when N availability is a yield limiting factor. To successfully use nitrate tissue testing as an indicator of the N status of plants, the effects of factors other than soil or fertilizer N on the nitrate concentration in the tested tissue must be understood. Diurnal effects on stalk nitrate content were studied in a greenhouse experiment, in which stalk samples were collected every two hours for 24 hours, and in a field study, where plants in an N‐fertilizer response experiment were sampled at sunrise and at mid‐day. A significant diurnal cycle was observed for stalk nitrate content in the greenhouse, with a peak at 0800 h and a low at 1400 h, but no diurnal effect was found in the field study, possibly due to plant stress from other environmental factors. In a second greenhouse study, stalk samples from seedlings in direct and 66% shaded nat...

Aerosol measurements at four background sites

Atmospheric monitoring stations are operated at Barrow, Alaska; Mauna Loa, Hawaii; American Samoa; and South Pole by the Geophysical Monitoring for Climatic Change program to measure the characteristics of gaseous and aerosol species under background conditions. A nearly continuous record of light‐scattering coefficient and condensation nuclei concentration measurements is available for Barrow since 1971, Mauna Loa since 1974, Samoa since 1977, and South Pole since 1974. The Barrow light‐scattering data exhibit a strong annual cycle with a maximum in winter and spring (the Arctic haze) and a minimum in summer. The Barrow condensation nuclei data exhibit a strong semiannual cycle with a maximum coinciding with that of light scattering and an additional maximum about August. The Mauna Loa light‐scattering data show a strong annual cycle with a maximum in April or May caused by long‐range transport of Asian desert dust. The Mauna Loa condensation nuclei data show no significant annual cycle. The Samoa light‐scattering and condensation nuclei data are representative of a clean marine atmosphere and exhibit no significant annual or diurnal cycle. The South Pole light‐scattering data show a complicated annual cycle with a maximum in the austral summer and a minimum about April. The austral winter is dominated by events most likely caused by the transport of sea salt in the troposphere from the coastal regions to the interior of the Antarctic continent. The South Pole condensation nuclei data show a repeatable annual cycle with a maximum in the austral summer and a minimum in the austral winter. Linear least squares trend analyses show no significant trend compared to the standard error about the regression line at any station.

Short-range forecasting of pollutant ground level concentration

Future legislation in developed countries may require short-range forecasting of pollutant ground level concentration. All available models describe concentration as a function of meteorological inputs. Extensive data from Naples of such inputs have been analysed and found to show highly significant diurnal cycles. The dominance of diurnal variations enables reliable short-range predictions of these terms to be made over 24 h, starting from a known state. A test on the pollutant ground level concentration forecast by introducing into diffusive models meteorological data predicted on one hand by diurnal cycle and on the other by routine methods has shown the advantage of our method.

DIURNAL EXCRETION OF Cr2O3 BY RUMINANTS WHEN ADMINISTERED IN SUSTAINED-RELEASE PELLETS

Two types of sustained-release pellets (S.R.P.) were developed for administering chromium oxide (Cr2O3) to cattle and sheep: an extruded pellet (E.S.R.P.) for cattle, dissolution time 4 to 5 days, containing about 10 g Cr2O3, and a pressed pellet (P.S.R.P.), dissolution time 16 to 20 days, containing about 32 g Cr2O3 for cattle and 20 g for sheep and calves. Both types of pellets were retained by animals kept indoors and fed either long or chopped forage. Animals on pasture regurgitated 50% or more of E.S.R.P. and about 10% of P.S.R.P. Specific gravity of E.S.R.P. was 1.7 and of P.S.R.P., 2.8.Administration of Cr2O3 in S.R.P. eliminated the statistically significant diurnal excretion cycles normally observed with conventional once or twice daily dosing of animals in stalls. Small but statistically significant (P &lt; 0.05) differences between grab samples of feces occurred with cattle on pasture grazed by free, strip, or mechanical (zero) systems.Sustained-release pellets are useful in experiments with animals kept in confinement but more general use is restricted because they cannot be made by commercial tabletting equipment and may be regurgitated by animals on pasture.

Variation of hourly winds at 35 to 65 kilometers during one day at Eglin Air Force Base, Florida

Harmonic analysis of 23 hourly Robin rocket soundings taken at Eglin AFB, Florida, on May 9–10, 1961, revealed statistically significant diurnal and semidiurnal cycles in winds between 35 and 65 km. These cycles doubled in amplitude through the layer. They can be related to the results of other investigations in a manner compatible with some but not all parts of current tidal theory. These cycles create a maximum in wind variability at a lag of 8 to 12 hours and significantly lower variability at 24 hours. The variability at a lag of 12 hours may be as large as that at 48 hours.