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A. Constantin and R. S. Johnson

Abstract

The problem of flow moving purely in the azimuthal direction on a sphere is considered. An exact solution for an incompressible (constant density), inviscid fluid, which admits a velocity profile below the surface and along the surface, is constructed; this can be regarded as a model for the Antarctic Circumpolar Current (ACC). The new approach adopted here is to model the processes that produce the observed structure of the ACC by the introduction of a nonconservative body force. It is shown that if the body force is conservative, then the governing equations necessarily lead to profiles that are quite unrealistic. However, with a suitable choice of body force, which reverts to conservative outside the ACC, any velocity profile of any width can be constructed as an exact solution of the system. A fairly simple choice is made in this note in order to present some specific results: a profile on the surface that is zero outside the arc of the ACC, with a maximum at its center and decaying with depth. It is shown that the methods developed here can be used to produce ever more complicated profiles to correspond to different data. Indeed, the basic example that this study introduces can be regarded as one of the jets that compose the ACC, and the results allow for any number of such jets. Although only one velocity profile is described, it is emphasized that many different choices, motivated by direct velocity observations in specific regions, are possible within the model. In conclusion, a few comments are made outlining the way in which this exact solution can be embedded within more general and complete discussions of the ACC and its properties.

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A. Constantin and R. S. Johnson

Abstract

A systematic development, based on the construction of an asymptotic solution of the Euler equation, written in rotating, spherical coordinates (φ,θ,r), is used to investigate the flows of the type seen in the neighborhood of the Pacific equator. First, it is shown that the observed poleward surface-flow structure away from the line of the equator is possible only if the flow evolves (changes) in the azimuthal direction. Then, allowing for variations in the azimuthal direction, the shallow-water, small-Rossby-number version of the problem, approximated close to the equator, leads to an asymptotic formulation that admits any prescribed azimuthal velocity profile u(θ,r) at some fixed longitude φ. The maximum extent of the flow region inside which we can describe in detail the velocity field is restricted by the size of the Rossby number. The analysis demonstrates that the meridional υ and vertical w velocity components are nonlinearly connected to u, and that all three velocity components appear at the same order in the leading (scaled) equations, even though the physical size of w is very much smaller than that of the other two components. An appropriate choice is made for u, at a given φ, and the corresponding complete three-dimensional flow field, which emerges from the interlinkage of the velocity components, is described; the thermocline is also added to the flow configuration. We compare these results with the available field data, demonstrating that this formulation captures all the main structures of the flow field, but also allows for many choices to be made that can be used to adjust the details of the flow and to model other, similar flows.

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A. Constantin and R. S. Johnson

Abstract

The general problem of an ocean on a rotating sphere is considered. The governing equations for an inviscid, incompressible fluid, written in spherical coordinates that are fixed at a point on the rotating Earth, together with the free surface and rigid bottom boundary conditions, are introduced. An exact solution of this system is presented; this describes a steady flow that is moving only in the azimuthal direction, with no variation in this direction. However, this azimuthal velocity component has an arbitrary variation with depth (i.e., radius), and so, for example, an Equatorial Undercurrent (EUC) can be accommodated. The pressure boundary condition at the free surface relates this pressure to the shape of the surface via a Bernoulli relation; this provides the constraint on the existence of a solution, although the restrictions are somewhat involved in spherical coordinates. To examine this constraint in more detail, the corresponding problems in model cylindrical coordinates (with the equator “straightened” to become a generator of the cylinder), and then in the tangent-plane version (with the β-plane approximation incorporated), are also written down. Both these possess similar exact solutions, with a Bernoulli condition that is more readily interpreted in terms of the choices available. Some simple examples of the surface pressure, and associated surface distortion, are presented. The relevance of these exact solutions to more complicated, and physically realistic, flow structures is briefly mentioned.

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S. Businger, R. Johnson, and R. Talbot

This paper provides an overview of the trials and successes in the development of an autonomous balloon instrument platform (smart balloon) and reviews scientific insights gained through its employment as a marker in a Lagrangian strategy during recent field experiments. The smart balloons are designed and constructed at the National Oceanic and Atmospheric Administration Air Resources Laboratory Field Research Division in collaboration with the University of Hawaii. In a 2004 field deployment a smart balloon carrying a miniature ozone sensor successfully crossed the Atlantic Ocean from Long Island, New York, to the African coast of Morocco. Significant progress has been made through field experiments such as this in our understanding of the relationships between the evolution of marine boundary layers and the chemistry of aerosol and gaseous constituents in clean and polluted air masses. Innovation in design and advances in instrument and communication technology have opened a dramatic new range of applications for the smart balloon in atmospheric research, including, for example, the interesting prospect of making observations very near the ocean surface in hurricanes and typhoons, which are not possible with research aircraft.

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J. D. McQuigg, S. R. Johnson, and J. R. Tudor

Abstract

A method is developed which can be used to produce estimates of electric power load diversity from samples of ambient daily mean temperature observations from a large interconnected power system. This method has several advantages, the most important of which is the comparative case with which homogenous samples of temperature data can be located. The method is believed to have important applications in long-term planning of large interconnected electric power systems.

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D. S. Arndt, M. O. Baringer, and M. R. Johnson

Editors note: For easy download the posted pdf of the State of the Climate for 2009 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

Abstract

The year was characterized by a transition from a waning La Niña to a strengthening El Niño, which first developed in June. By December, SSTs were more than 2.0°C above average over large parts of the central and eastern equatorial Pacific. Eastward surface current anomalies, associated with the El Niño, were strong across the equatorial Pacific, reaching values similar to the 2002 El Niño during November and December 2009. The transition from La Niña to El Niño strongly influenced anomalies in many climate conditions, ranging from reduced Atlantic basin hurricane activity to large scale surface and tropospheric warmth.

Global average surface and lower-troposphere temperatures during the last three decades have been progressively warmer than all earlier decades, and the 2000s (2000–09) was the warmest decade in the instrumental record. This warming has been particularly apparent in the mid- and high-latitude regions of the Northern Hemisphere and includes decadal records in New Zealand, Australia, Canada, Europe, and the Arctic. The stratosphere continued a long cooling trend, except in the Arctic.

Atmospheric greenhouse gas concentrations continued to rise, with CO2 increasing at a rate above the 1978 to 2008 average. The global ocean CO2 uptake flux for 2008, the most recent year for which analyzed data are available, is estimated to have been 1.23 Pg C yr−1, which is 0.25 Pg C yr−1 smaller than the long-term average and the lowest estimated ocean uptake in the last 27 years. At the same time, the total global ocean inventory of anthropogenic carbon stored in the ocean interior as of 2008 suggests an uptake and storage of anthropogenic CO2 at rates of 2.0 and 2.3 ±0.6 Pg C yr−1 for the decades of the 1990s and 2000s, respectively. Total-column ozone concentrations are still well below pre-1980 levels but have seen a recent reduction in the rate of decline while upper-stratospheric ozone showed continued signs of ongoing slow recovery in 2009. Ozone-depleting gas concentrations continued to decline although some halogens such as hydrochlorofluorocarbons are increasing globally. The 2009 Antarctic ozone hole was comparable in size to recent previous ozone holes, while still much larger than those observed before 1990. Due to large interannual variability, it is unclear yet whether the ozone hole has begun a slow recovery process.

Global integrals of upper-ocean heat content for the last several years have reached values consistently higher than for all prior times in the record, demonstrating the dominant role of the oceans in the planet's energy budget. Aside from the El Niño development in the tropical Pacific and warming in the tropical Indian Ocean, the Pacific Decadal Oscillation (PDO) transitioned to a positive phase during the fall/winter 2009. Ocean heat fluxes contributed to SST anomalies in some regions (e.g., in the North Atlantic and tropical Indian Oceans) while dampening existing SST anomalies in other regions (e.g., the tropical and extratropical Pacific). The downward trend in global chlorophyll observed since 1999 continued through 2009, with current chlorophyll stocks in the central stratified oceans now approaching record lows since 1997.

Extreme warmth was experienced across large areas of South America, southern Asia, Australia, and New Zealand. Australia had its second warmest year on record. India experienced its warmest year on record; Alaska had its second warmest July on record, behind 2004; and New Zealand had its warmest August since records began 155 years ago. Severe cold snaps were reported in the UK, China, and the Russian federation. Drought affected large parts of southern North America, the Caribbean, South America, and Asia. China suffered its worst drought in five decades. India had a record dry June associated with the reduced monsoon. Heavy rainfall and floods impacted Canada, the United States, the Amazonia and southern South America, many countries along the east and west coasts of Africa, and the UK. The U.S. experienced its wettest October in 115 years and Turkey received its heaviest rainfall over a 48-hr period in 80 years.

Sea level variations during 2009 were strongly affected by the transition from La Niña to El Niño conditions, especially in the tropical Indo-Pacific. Globally, variations about the long-term trend also appear to have been influenced by ENSO, with a slight reduction in global mean sea level during the 2007/08 La Niña event and a return to the long-term trend, and perhaps slightly higher values, during the latter part of 2009 and the current El Niño event. Unusually low florida Current transports were observed in May and June and were linked to high sea level and coastal flooding along the east coast of the United States in the summer. Sea level significantly decreased along the Siberian coast through a combination of wind, ocean circulation, and steric effects. Cloud and moisture increased in the tropical Pacific. The surface of the western equatorial Pacific freshened considerably from 2008 to 2009, at least partially owing to anomalous eastward advection of fresh surface water along the equator during this latest El Niño. Outside the more variable tropics, the surface salinity anomalies associated with evaporation and precipitation areas persisted, consistent with an enhanced hydrological cycle.

Global tropical cyclone (TC) activity was the lowest since 2005, with six of the seven main hurricane basins (the exception is the Eastern North Pacific) experiencing near-normal or somewhat below-normal TC activity. Despite the relatively mild year for overall hurricane activity, several storms were particularly noteworthy: Typhoon Morakot was the deadliest typhoon on record to hit Taiwan; Cyclone Hamish was the most intense cyclone off Queensland since 1918; and the state of Hawaii experienced its first TC since 1992.

The summer minimum ice extent in the Arctic was the third-lowest recorded since 1979. The 2008/09 boreal snow cover season marked a continuation of relatively shorter snow seasons, due primarily to an early disappearance of snow cover in spring. Preliminary data indicate a high probability that 2009 will be the 19th consecutive year that glaciers have lost mass. Below normal precipitation led the 34 widest marine terminating glaciers in Greenland to lose 101 km2 ice area in 2009, within an annual loss rate of 106 km2 over the past decade. Observations show a general increase in permafrost temperatures during the last several decades in Alaska, northwest Canada, Siberia, and Northern Europe. Changes in the timing of tundra green-up and senescence are also occurring, with earlier green-up in the High Arctic and a shift to a longer green season in fall in the Low Arctic.

The Antarctic Peninsula continues to warm at a rate five times larger than the global mean warming. Associated with the regional warming, there was significant ice loss along the Antarctic Peninsula in the last decade. Antarctic sea ice extent was near normal to modestly above normal for the majority of 2009, with marked regional contrasts within the record. The 2008/09 Antarctic-wide austral summer snowmelt was the lowest in the 30-year history.

This 20th annual State of the Climate report highlights the climate conditions that characterized 2009, including notable extreme events. In total, 37 Essential Climate Variables are reported to more completely characterize the State of the Climate in 2009.

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S. R. Johnson, James D. McQuigg, and Thomas P. Rothrock

Abstract

The electric power industry has long been known to be sensitive to weather events. In particular, daily temperatures in distribution areas are known to affect electric power consumption. In this paper the relationship between power consumption and daily temperatures is estimated using simple regression techniques. The resulting relationships permit an investigation of the consequences of temperature modification for 14 midwestern electric power production companies. Comparisons between power production costs for observed and modified historical and experimentally generated temperature series suggest that changes of 3–5F in average daily temperature can reduce costs substantially. Exact differentials in production cost which can be attributed to temperature modification are presented so as to be useful in firm, industry and public policy decisions.

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EMIL D. ATTANASI, S. R. JOHNSON, SHARON LeDUC, and JAMES D. McQUIGG

Abstract

Certain activities of highway construction are particularly sensitive to such weather conditions as soil moisture, precipitation, and daily temperature. Regression analysis is used to obtain three alternative probability models designed to translate observed weather conditions into probabilities for carrying out construction activities. The models were developed using generalized least squares, normit analysis, and logit analysis. The generalized least squares method was the most convenient computationally, but it had severe interpretative disadvantages. The results obtained by logit analysis gave the desired probabilistic interpretation most readily and had the best predictive ability. Comparison of sample observation and predicted work probabilities for common excavation during wet and dry months indicated that the logit analysis model could accurately translate weather conditions into probabilities that work would take place. Models for paving and asphalt work and for bridge and drainage structure are also estimated using logit analysis. These estimates indicate a strong sensitivity of the latter category of work to precipitation conditions. Such models may aid contract letting agencies is planning payment schedules, penalty clauses, and completion dates for new roads; construction firms may find such models valuable in planning effective use of men and equipment.

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W-K. Tao, C-L. Shie, J. Simpson, S. Braun, R. H. Johnson, and P. E. Ciesielski

Abstract

The two-dimensional version of the Goddard Cumulus Ensemble (GCE) model is used to simulate two South China Sea Monsoon Experiment (SCSMEX) convective periods [18–26 May (prior to and during the monsoon onset) and 2–11 June (after the onset of the monsoon) 1998]. Observed large-scale advective tendencies for potential temperature, water vapor mixing ratio, and horizontal momentum are used as the main forcing in governing the GCE model in a semiprognostic manner. The June SCSMEX case has stronger forcing in both temperature and water vapor, stronger low-level vertical shear of the horizontal wind, and larger convective available potential energy (CAPE).

The temporal variation of the model-simulated rainfall, time- and domain-averaged heating, and moisture budgets compares well to those diagnostically determined from soundings. However, the model results have a higher temporal variability. The model underestimates the rainfall by 17% to 20% compared to that based on soundings. The GCE model-simulated rainfall for June is in very good agreement with the Tropical Rainfall Measuring Mission (TRMM), precipitation radar (PR), and the Global Precipitation Climatology Project (GPCP). Overall, the model agrees better with observations for the June case rather than the May case.

The model-simulated energy budgets indicate that the two largest terms for both cases are net condensation (heating/drying) and imposed large-scale forcing (cooling/moistening). These two terms are opposite in sign, however. The model results also show that there are more latent heat fluxes for the May case. However, more rainfall is simulated for the June case. Net radiation (solar heating and longwave cooling) are about 34% and 25%, respectively, of the net condensation (condensation minus evaporation) for the May and June cases. Sensible heat fluxes do not contribute to rainfall in either of the SCSMEX cases. Two types of organized convective systems, unicell (May case) and multicell (June case), are simulated by the model. They are determined by the observed mean U wind shear (unidirectional versus reverse shear profiles above midlevels).

Several sensitivity tests are performed to examine the impact of the radiation, microphysics, and large-scale mean horizontal wind on the organization and intensity of the SCSMEX convective systems.

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S. L. Durden, M. A. Fischman, R. A. Johnson, A. J. Chu, M. N. Jourdan, and S. Tanelli

Abstract

Measurement of precipitation Doppler velocity by spaceborne radar is complicated by the large velocity of the satellite platform. Even if successive pulses are well correlated, the velocity measurement may be biased if the precipitation target does not uniformly fill the radar footprint. It has been previously shown that the bias in such situations can be reduced if full spectral processing is used. The authors present a processor based on field-programmable gate array (FPGA) technology that can be used for spectral processing of data acquired by future spaceborne precipitation radars. The requirements for and design of the Doppler processor are addressed. Simulation and laboratory test results show that the processor can meet real-time constraints while easily fitting in a single FPGA.

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