Dynamic spectra processed from data recorded on magnetic tape at the mid-latitude Ralston station (Alberta) in 1967 have been studied in detail. The Pc3,4 pulsations appear to behave in a much more complicated manner than reported by other observers at low-latitude stations. The variation of the Pc3,4 frequency at Ralston assumes different forms from one day to another, the pattern depending largely upon the general level of magnetic disturbance represented by the K(p)-index. It appears, however, that most of the Pc3,4 spectra analysed may be classified into one of, or a combination of, four well-defined diurnal patterns under steady magnetospheric conditions. An interpretation is offered to explain the existence as well as the fine structure of these four diurnal patterns. The crux of the present interpretation is that Ralston, under moderate magnetospheric agitation, may pick up micropulsation activities originating from the plasmasphere and/or the plasmatrough depending upon its position relative to the plasmapause. Eigen oscillations of modified Alfven mode (poloidal oscillation) in these two magnetospheric regions are considered to be the prime sources of the ground observed Pc3,4 magnetic pulsations. Such suggestion is reinforced by observations made simultaneously at other mid- and high-latitude stations. Other morphological properties of Pc3 and Pc4 are discussed in the light of the new interpretation. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Approved for public release; distribution unlimited / In conjunction with the Huntington Beach Phase III Investigation, the diurnal variability in the wind and ocean currents from July 1 - October 12, 2001 over the San Pedro Shelf is investigated. Results suggest that the diurnal currents are driven by the diurnal winds but that the strength of the ocean response is modulated by the low frequency flow regime. The spectral peak of the near-surface currents is at the diurnal frequency, which is below the inertial frequency (1.107 cpd). The diurnal currents are surface-intensified, decaying with depth to a minimum at 10-13 m and increasing slightly in strength below that. The near-surface diurnal currents are in phase across the shelf, and are close to in phase with the winds over the shelf. The amplitude modulation of the diurnal energy of the ocean currents is correlated with the direction of the low frequency flow along the shelf;the energy is enhanced when the flow is equatorward, and weak when the flow is poleward. The amplitudes of the diurnal near-surface currents are also correlated with the diurnal winds. However, the low frequency currents and winds are not well correlated. / Lieutenant, United States Navy

Four portable magnetometer stations were set up at intervals of 80 - 100 kilometers along an east-west profile running from Tofino on the west coast of Vancouver Island to Abbotsford on the mainland in order to study the spatial dependence of the coastal anomaly. These were supplemented by records from the permanent Victoria Magnetic Observatory. The Tofino-Abbotsford chain extends and partly overlaps an earlier chain of stations set up to search for geomagnetic anomalies, along an east-west profile from Lethbridge, Alberta to Vancouver, British Columbia, The coastal anomaly recorded at Tofino is observed exclusively in the vertical component, diminishing rapidly inland and reaching its maximum value when the inducing field changes in approximately an east-west direction with a frequency between one and two cycles per hour. The horizontal and vertical variations are in a ratio of two to one at the coast which is in agreement with induction ratios calculated at coastlines in Australia and California. The directional dependence and limited spatial extent of the anomaly indicate a rather shallow conductivity discontinuity, at most 100 kilometers deep, running approximately parallel to the continental shelfline. Since at the maximum response frequency the upper mantle beneath the ocean is largely shielded by the overlying wedge of sea water, the anomaly is thought to be mostly due to the conductivity contrast between the deep ocean and the continent. The diurnal geomagnetic variations which pass through the surface layers virtually unattenuated show at least a twenty five percent enhancement in the vertical component from Abbotsford to Tofino. This anomaly perhaps reflects a change in upper mantle conductivity more accurately than does the higher frequency Tofino anomaly. At a still higher frequency of three cycles per hour where the Tofino anomaly is already reduced, there is a small anomaly in the vertical component at Westham Island on the east side of Georgia Strait which is completely absent at lower frequencies. The influence of a shallow body of sea water such as Georgia Strait is expected to be small. Hence this anomaly is probably due to a conductivity structure beneath the Strait in the crust or upper mantle. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Molecular nitrogen is a highly abundant element in the atmosphere; it is stable and not very reactive. Anthropogenic activities have caused greater concentrations of nitrogen-containing compounds that are highly reactive and ultimately toxic. Reactive nitrogen concentrations have become a growing concern on the South African Highveld, with satellite images indicating very high nitrogen dioxide concentrations in the region. This study investigates the nitrogen budget on the Highveld through the analysis of the nitrogen species emitted into the atmosphere on a temporal scale as well as the atmospheric conversion, transport and removal of these species. Data was collected at Elandsfontein monitoring site, which is centrally located on the industrialised Highveld. The formation and interaction of nitric oxide (NO), nitrogen dioxide (NO2), and nitrate (NO3) are a major focus in the study. NOx concentrations are higher in winter (6.5 to 8.5 μg.m-3) as a result of stable atmospheric conditions. NO3 concentrations also peak during winter (3.5 to 5.5 μg.m-3), with a distinct biomass burning peak during July and August. Diurnally, NOx concentrations indicate a tall-stack industrial source, with concentrations peaking at midday. NO3 concentrations are higher at night and lower during the day, as during the day the NO3 radical is rapidly photolysed and nitrates cannot be produced. Case studies indicate that the conversion rate of NO to NO2 is highly variable as a result of varying atmospheric factors. These rates range from 11% to 59% per hour. Rates of dry deposition of NO, NO2 and NO3 are generally higher during winter as a result of higher concentrations and increased atmospheric stability, which prevents transport out of the region. Nitrogen is predominantly deposited as NO2 throughout the year, except during spring when NO3 deposition dominates. The total amount of nitrogen deposited to the Mpumalanga Highveld region is in the range of 6.7 to 13.1 kg ha-1 yr-1, which is well below the stipulated critical load value. Such deposition therefore does not pose significant threats to the natural environment on the Highveld. Between 4% and 14% of the total emitted nitrogen on the Highveld is deposited to the surface via wet and dry deposition. The remainder stays in the atmosphere and is advected out of the region.

The Mars Pathfinder (MPF) arrived on the Martian surface on 4 July 1997 to become only the third successful landed mission to Mars, recording surface meteorological data intermittently over a period of 83 Martian days ("sols"). The in situ observations made by the MPF meteorology (MET) experiment were recorded at much greater precision than those of the previous missions, Viking Landers 1 and 2. These observations have been analyzed, focusing primarily upon the four so-called "Presidential" sessions, which each covered a complete diurnal cycle. The signature of very strong convective activity was seen in the temperature data, beginning soon after sunrise with temperatures changing as much as 14.39 K over the four-second interval between observations, and ceasing in late afternoon at the collapse of the boundary layer. Less extreme variability occurred at most other times of day and night. Examination of the first ten tidal pressure harmonic amplitudes for each Presidential session revealed strong diurnal and semidiurnal amplitudes and smaller, yet significant, amplitudes at the higher tidal frequencies. The normalized diurnal amplitude was slightly more than 1.7% for one session and averaged ~2.5% for the other three sessions. The semidiurnal amplitude averaged ~1.3%. A pattern in the tidal pressure harmonic amplitudes exists, in which odd-numbered harmonics (excluding the diurnal frequency) have smaller amplitudes than those of the next lower and next higher, even-numbered harmonics. Wind direction data for one Presidential session show very high variability throughout most of the diurnal cycle, the most intense activity occurring during the daytime convective period. A generally clockwise rotation of the mean wind direction was observed throughout the session. Temperature and wind data were examined closely for evidence of contamination of the temperature data by thermal effects of the lander itself. No evidence was found for such "lander interference" in the morning, but lander interference may have occurred in the afternoon of the session examined. A study of a numerical simulation by the NASA Ames Mars General Circulation Model (MGCM) showed prominent minima and maxima, resembling those observed by MPF, in the diurnal pressure cycles of simulated sols corresponding to the Presidential sessions. Also well simulated in each sol is the very rapid increase in surface pressure immediately after the daily minimum. Maps of diurnal and semidiurnal tidal amplitudes for the simulated Presidential sols show that tidal harmonic amplitudes are very spatially dependent, and that large changes in the harmonic amplitudes at any given location are likely to result if the global amplitude pattern for one or more frequencies undergoes small shifts in areographic location. Simulated temperature has a classic "red" power spectrum, while simulated pressure power is concentrated in the tidal frequency range. These spectral shapes are roughly consistent with those computed from the MPF Presidential sessions. The ratios of simulated to observed temperature power spectral estimates for frequencies from 1 to 50 cycles/sol show that the MGCM's simulated temperature variability is too low at all frequencies and especially so at higher frequencies. / Graduation date: 2003

Atmospheric inversion has recently become an important tool in estimating CO2 sinks and sources albeit that the existing inversion results are often uncertain and differ considerably in terms of the spatiotemporal variations of the inverted carbon flux. More measurements combined with terrestrial ecosystem information are expected to improve the estimates of global surface carbon fluxes which are used to understand the relationships between variabilities of the terrestrial carbon cycle and anomalies of climatic factors. Inversions using more observations have often been hampered by the intense diurnal variations of CO2 concentrations at continental sites. Diurnal variations of the surface flux are included with atmospheric boundary dynamics in order to improve the atmospheric inversion accuracy. Modeling experiments conducted in this study show that inverse estimates of the carbon flux are more sensitive to the variation of the atmospheric boundary layer dynamics than to the diurnal variation in the surface flux. It is however generally better to consider both diurnal variations in the inversion than to consider only either of them. Forest carbon dynamics is closely related to stand age. This useful terrestrial ecosystem information has been used as an additional constraint to the atmospheric inversion. The inverse estimates with this constraint over North America exhibit an improved correlation with carbon sink estimates derived from eddy-covariance measurements and remotely-sensed data, indicating that the use of age information can improve the accuracy of atmospheric inversions. Terrestrial carbon uptake is found mainly in northern land, and a strong flux density is revealed in southeastern North America in an improved multi-year inversion from 2002 to 2007. The global interannual variability of the flux is dominated by terrestrial ecosystems. The interannual variabilities of regional terrestrial carbon cycles could be mostly explained by monthly anomalies of climatic conditions or short-time extreme meteorological events. Monthly anomalies of the inverted fluxes have been further analyzed against the monthly anomalies of temperature and precipitation to quantitatively assess the responses of the global terrestrial carbon cycle to climatic variabilities and to determine the dominant mechanisms controlling the variations of terrestrial carbon exchange.

Atmospheric inversion has recently become an important tool in estimating CO2 sinks and sources albeit that the existing inversion results are often uncertain and differ considerably in terms of the spatiotemporal variations of the inverted carbon flux. More measurements combined with terrestrial ecosystem information are expected to improve the estimates of global surface carbon fluxes which are used to understand the relationships between variabilities of the terrestrial carbon cycle and anomalies of climatic factors. Inversions using more observations have often been hampered by the intense diurnal variations of CO2 concentrations at continental sites. Diurnal variations of the surface flux are included with atmospheric boundary dynamics in order to improve the atmospheric inversion accuracy. Modeling experiments conducted in this study show that inverse estimates of the carbon flux are more sensitive to the variation of the atmospheric boundary layer dynamics than to the diurnal variation in the surface flux. It is however generally better to consider both diurnal variations in the inversion than to consider only either of them. Forest carbon dynamics is closely related to stand age. This useful terrestrial ecosystem information has been used as an additional constraint to the atmospheric inversion. The inverse estimates with this constraint over North America exhibit an improved correlation with carbon sink estimates derived from eddy-covariance measurements and remotely-sensed data, indicating that the use of age information can improve the accuracy of atmospheric inversions. Terrestrial carbon uptake is found mainly in northern land, and a strong flux density is revealed in southeastern North America in an improved multi-year inversion from 2002 to 2007. The global interannual variability of the flux is dominated by terrestrial ecosystems. The interannual variabilities of regional terrestrial carbon cycles could be mostly explained by monthly anomalies of climatic conditions or short-time extreme meteorological events. Monthly anomalies of the inverted fluxes have been further analyzed against the monthly anomalies of temperature and precipitation to quantitatively assess the responses of the global terrestrial carbon cycle to climatic variabilities and to determine the dominant mechanisms controlling the variations of terrestrial carbon exchange.

In the current study, we have presented a systematic analysis of the diurnal cycle of rainfall over the Indian region using satellite observations, and evaluated the ability of the Weather Research and Forecasting Model (WRF) to simulate some of the salient features of the observed diurnal characteristics of rainfall. Using high resolution simulations, we also investigate the underlying mechanisms of some of the observed diurnal signatures of rainfall. Using the Tropical Rain-fall Measuring Mission (TRMM) 3-hourly, 0.25 ×0.25 degree 3B42 rainfall product for nine years (1999-2007), we extract the finer spatial structure of the diurnal scale signature of Indian summer monsoon rainfall. Using harmonic analysis, we construct a signal corresponding to diurnal and sub-diurnal variability. Subsequently, the 3-hourly time-period or the octet of rain-fall peak for this filtered signal, referred to as the “peak octet,” is estimated with care taken to eliminate spurious peaks arising out of Gibbs oscillations. Our analysis suggests that over the Bay of Bengal, there are three distinct modes of the peak octet of diurnal rainfall corresponding to 1130, 1430 and 1730 IST, from north central to south Bay. This finding could be seen to be consistent with southward propagation of the diurnal rainfall pattern reported by earlier studies. Over the Arabian sea, there is a spatially coherent pattern in the mode of the peak octet (1430 IST), in a region where it rains for more than 30% of the time. In the equatorial Indian Ocean, while most of the western part shows a late night/early morning peak, the eastern part does not show a spatially coherent pattern in the mode of the peak octet, owing to the occurrence of a dual maxima (early morning and early/late afternoon). The Himalayan foothills were found to have a mode of peak octet corresponding to 0230 IST, whereas over the Burmese mountains and the Western Ghats (west coast of India) the rainfall peaks during late afternoon/early evening (1430-1730 IST). This implies that the phase of the diurnal cycle over inland orography (e.g., Himalayas) is significantly different from coastal orography (e.g., Western Ghats). We also find that over the Gangetic plains, the peak octet is around 1430 IST, a few hours earlier compared to the typical early evening maxima over land. The second part of our study involves evaluating the ability of the Weather Research and Fore-casting Model (WRF) to simulate the observed diurnal rainfall characteristics. It also includes conducting high resolution simulations to explore the underlying physical mechanisms of the observed diurnal signatures of rainfall. The model (at 54km resolution) is integrated for the month of July 2006 since this period was particularly favourable for the study of diurnal cycle. We first evaluate the sensitivity of the model to the prescribed sea surface temperature (SST) by using two different SST datasets, namely Final Analyses (FNL) and Real-time Global (RTG). The overall performance of RTG SST was found to be better than FNL, and hence it was used for further model simulations. Next, we investigated the impact of different parameterisations (convective, microphysical, boundary layer, radiation and land surface) on the simulation of diurnal cycle of rainfall. Following this sensitivity study, we identified the suite of physical parameterisations in the model that “best” reproduces the observed diurnal characteristics of Indian monsoon rainfall. The “best” model configuration was used to conduct two nested simulations with one-way, three-level nesting (54-18-6km) over central India and Bay of Bengal. While the 54km and 18km simulations were conducted for July 2006, the 6km simulation was carried out for the period 18-24 July 2006. This period was chosen for our study since it is composed of an active period (19-21 July 2006), followed by a break period (22-24 July 2006). At 6km grid-spacing the model is able to realistically simulate the active and break phases in rainfall. During the chosen active phase, we find that the observed rainfall over central India tends to reach a maximum in the late night/early morning hours. This is in contrast to the observed climatological diurnal maxima of late evening hours. Interestingly, the 6km simulation for the active phase is able to reproduce this late night/early morning maxima. Upon further analysis, we find that this is because of the strong moisture convergence at the mid-troposphere during 2030-2330 IST, leading to the rainfall peak seen during 2330-0230 IST. Based on our analysis, we conclude that during both active and break phases of summer monsoon, mid-level moisture convergence seems to be one of the primary factors governing the phase of the diurnal cycle of rainfall. Over the Bay of Bengal, the 6km model simulation is in very good agreement with observations, particularly during the active phase. The southward propagation observed during 19-20 July 2006, which was not captured by the coarse resolution simulation (54km), is exceedingly well captured by the 6km simulation. The positive anomalies in specific humidity attain a maxima during 2030-0230 IST in the north and during 0830-1430 IST in the south. This confirms the role of moisture convergence in the southward propagation of rainfall. Equally importantly we find that while low level moisture convergence is dominant in the north Bay, it is the mid-level moisture convergence that is predominant in the south Bay.

Thesis (Ph.D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (p. 217-222). / Estimation of the upper ocean heat budget from one year of observations at a moored array in the north central Arabian Sea shows a rough balance between the horizontal advection and time change in heat when the one-dimensional balance between the surface heat flux and oceanic heat content breaks down. The two major episodes of horizontal advection, during the early northeast (NE) and late southwest (SW) monsoon seasons, are both associated with the propagation of mesoscale eddies. During the NE monsoon, the heat fluxes within the mixed layer are not significantly different from zero, and the large heat flux comes from advected changes in the thermocline depth. During the SW monsoon a coastal filament exports recently upwelled water from the Omani coast to the site of the array, 600 km offshore. Altimetry shows mildly elevated levels of surface eddy kinetic energy along the Arabian coast during the SW monsoon, suggesting that such offshore transport may be an important component of the Arabian Sea heat budget. The sea surface temperature (SST) and mixed layer depth are observed to respond to high frequency (HF, diurnal to atmospheric synoptic time scales) variability in the surface heat flux and wind stress. The rectified effect of this HF forcing is investigated in a three-dimensional reduced gravity thermodynamic model of the Arabian Sea and Indian Ocean. Both the HF heat and wind forcing act locally to increase vertical mixing in the model, reducing the SST. Interactions between the local response to the surface forcing, Ekman divergences, and remotely propagated signals in the model can reverse this, generating greater SSTs under HF forcing, particularly at low latitudes. The annual mean SST, however, is lowered under HF forcing, changing the balance between the net surface heat flux (which is dependent on the SST) and the meridional heat flux in the model. A suite of experiments with one-dimensional upper ocean models with different representations of vertical mixing processes suggests that the rectified effect of the diurnal heating cycle is dependent on the model, and overstated in the formulation used in the three-dimensional model. / by Albert Sok Fischer. / Ph.D.