Thursday, December 6, 2012

The variance spectrum

The variance spectrum of y is: where F is the variance of the white noise forcing and w is the frequency, Sony VAIO VPCF127HGBI Battery an implication of this equation is that at short time scales (w>>λ) the variance of the ocean temperature increase with the square of the period while at longer timescales(w<<λ, ~150 months) the damping process dominates and limits sea surface temperature anomalies so that the spectra became white. Sony VAIO VPCF137HG/BI Battery Thus an atmospheric white noise generates SST anomalies at much longer timescales but without spectral peaks. Modeling studies suggest that this process contribute to as much as 1/3 of the PDO variability at decadal timescales. Several dynamic oceanic mechanisms and SST-air feedback may contribute to the observed decadal variability in the North Pacific Ocean. Sony VAIO VGN-SR51MF/W Battery SST variability is stronger in the Kuroshio Oyashio extension (KOE) region and is associated with changes in the KOE axis and strength,[6] that generates decadal and longer time scales SST variance but without the observed magnitude of the spectral peak at ~10 years, and SST-air feedback. Sony VAIO VGN-SR51MR Battery Remote reemergence occurs in regions of strong current such as the Kuroshio extension and the anomalies created near the Japan may reemerge the next winter in the central pacific. Saravanan and McWilliamshave demonstrated that the interaction between spatially coherent atmospheric forcing patterns and an advective ocean shows periodicities at preferred Sony VAIO VGN-SR59VG Battery time scales when non-local advective effects dominates over the local sea surface temperature damping. This "advective resonance" mechanism may generate decadal SST variability in the Eastern North Pacific associated with the anomalous Ekman advection and surface heat flux. Sony VAIO VGN-SR59VG/H Battery Dynamic gyre adjustments are essential to generate decadal SST peaks in the North Pacific, the process occurs via westward propagating oceanic Rossby waves that are forced by wind anomalies in the central and eastern Pacific Ocean. The quasigeostrophic equation for long non-dispersive Rossby Waves forced by large scale wind stress can be written as: Sony VAIO VGN-SR70B/S Battery where h is the upper-layer thickness anomaly, τ is the wind stress, c is the Rossby wave speed that depends on latitude, ρ0 is the density of sea water and f0is the Coriolis parameter at a reference latitude. Sony VAIO VGN-SR72B/P Battery The response time scale is set by the Rossby waves speed, the location of the wind forcing and the basin width, at the latitude of the Kuroshio Extension c is 2.5 cm s−1 and the dynamic gyre adjustement timescale is ~(5)10 years if the Rossby wave was initiated in the (central)eastern Pacific Ocean. Sony VAIO VGN-SR72B/S Battery If the wind white forcing is zonally uniform it should generate a red spectrum in which h variance increase with the period and reaches a constant amplitude at lower frequencies without decadal and interdecadal peaks, however low frequencies atmospheric circulation tends to be dominated by fixed spatial patterns so that wind forcing is not zonally uniform, Sony VAIO VGN-SR73JB/S Battery if the wind forcing is zonally sinusoidal then decadal peaks occurs due to resonance of the forced basin-scale Rossby waves. The propagation of h anomalies in the western pacific changes the KOE axis and strength[6] and impact sst due to the anomalous geostrophic heat transport. Sony VAIO VGN-SR74FB/S Battery Recent studies[6][16] suggest that Rossby waves excited by the Aleutian low propagates the PDO signal from the North Pacific to the KOE through changes in the KOE axis while Rossby waves associated with the NPO propagates the North Pacific Gyre oscillation signal through changes in the KOE strength. Sony VAIO VGN-SR90FS Battery The PDO index has been reconstructed using tree rings and other hydrologically sensitive proxies from west North America and Asia. MacDonald and Case[19] reconstructed the PDO back to 993 using tree rings from California and Alberta. Sony VAIO VGN-SR90NS Battery The index shows a 50-70 year periodicity but this is a strong mode of variability only after 1800, a persistent negative phase occurred during medieval times (993-1300) which is consistent with la nina conditions reconstructed in the tropical Pacific[20]and multi-century droughts in the South-West United States.[21] Sony VAIO VGN-SR90S Battery Several regime shifts are apparent both in the reconstructions and instrumental data, during the 20th century regime shifts associated with concurrent changes in SST, SLP, land precipitation and ocean cloud cover occurred in 1924/1925,1945/1946 and 1976/1977:[22] Sony VAIO VGN-SR90US Battery
  • 1750: PDO displays an unusually strong oscillation.[3]
  • 1924/1925: PDO changed to a "warm" phase.[22]
1945/1946: The PDO changed to a "cool" phase, the pattern of this regime shift is similar to the 1970s episode with maximum amplitude in the subarctic and subtropical front but with a greater signature near the Japan while the 1970s shift was stronger near the American west coast.Sony VAIO VGN-SR91NS Battery
  • 1976/1977: PDO changed to a "warm" phase.[24]
1988/1989:A weakening of the Aleutian low with associated SST changes was observed,[25] in contrast to others regime shifts this change appears to be related to concurrent extratropical oscillation in the North Pacific and North Atlantic rather than tropical processes.Sony VAIO VGN-SR91PS Battery 1997/1998: Several changes in Sea surface temperature and marine ecosystem occurred in the North Pacific after 1997/1998, in contrast to prevailing anomalies observed after the 1970s shift SST declined along the United States west coast and substantial changes in the populations of salmon, Sony VAIO VGN-SR91S Battery anchovy and sardine were observed,[27] however the spatial pattern of the SST change was different with a meridional SST seesaw in the central and western Pacific that resemble a strong shift in the North Pacific Gyre Oscillation rather than the PDO structure, this pattern dominated much of the North Pacific SST variability after 1989. Sony VAIO VGN-SR91US Battery NOAA's forecast [1] use a linear inverse modeling (LIM)[29] method to predict the PDO, LIM assumes that the PDO can be separated into a linear deterministic component and a non-linear component represented by random fluctuations. Much of the LIM PDO predictability arises from ENSO and the global trend rather than extra-tropical processes and is thus limited to ~4 season, Sony VAIO VGN-SR92NS Battery the prediction is consistent with the seasonal footprinting mechanism[30] in which an optimal SST structure evolve into the ENSO mature phase 6–10 months later that subsequently impact the North Pacific Ocean SST via the atmospheric bridge. Skills in predicting decadal PDO variability could arise from taking into account the impact of the externally forced[31] and internally generated[32] Pacific variability. Sony VAIO VGN-SR92PS Battery An anticyclone (that is, opposite to a cyclone) is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere".[1] Sony VAIO VGN-SR92S Battery Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-basedhaze under their base. Sony VAIO VGN-SR92US Battery Anticyclones aloft can form within warm core lows, such as tropical cyclones, due to descending cool air from the backside of upper troughs, such as polar highs, or from large scale sinking, such as the subtropical ridge. Sir Francis Galton first discovered anticyclones in the 1860s while studying meteorology. Sony VAIO VGN-SR93DS Battery Preferred areas within a synopticflow pattern in higher levels of the troposphere are beneath the western side of troughs, or dips in the Rossby wavepattern. High-pressure systems are alternatively referred to as anticyclones. Their circulation is sometimes referred to as cum sole.Sony VAIO VGN-SR93JS Battery The subtropical ridge forms due to the Hadley cell circulation between the equator and the subtropics of the Northern Hemisphere and Southern Hemisphere. Upper-level high pressure areas lie over tropical cyclones due to their warm core nature. Surface anticyclones form due to downward motion through the troposphere, the atmospheric layer where weather occurs. Sony VAIO VGN-SR93PS Battery Preferred areas within a synoptic flow pattern in higher levels of the troposphere are beneath the western side of troughs. On weather maps, these areas show converging winds (isotachs), also known as confluence, or converging height lines near or above the level of non-divergence, Sony VAIO VGN-SR93YS Battery which is near the 500 hPa pressure surface about midway up through the troposphere.Because they weaken in intensity with height, these high pressure systems are cold.Heating of the earth near the equator leads to large amounts of upward motion and convection along the monsoon trough orIntertropical convergence zone. Sony VAIO VGN-SR94FS Battery The divergence over the near-equatorial trough leads to air rising and moving away from the equator aloft. As it moves towards the Mid-Latitudes, the air cools and sinks, which leads to subsidence near the 30th parallel of both hemispheres. This circulation is known as the Hadley cell and leads to the formation of the subtropical ridge. Sony VAIO VGN-SR94GS Battery Many of the world's deserts are caused by these climatological high-pressure areas.[5] Because these anticyclones strengthen with height, they are known as warm core ridges. The development of anticyclones aloft occurs in warm core cyclones, such as tropical cyclones, when latent heat caused by the formation of clouds is released aloft, Sony VAIO VGN-SR94HS Battery which increases air temperatures and the resultant atmospheric thickness of the layer, which increases high pressure aloft which acts to evacuate their outflow.In the absence of rotation, the wind tends to blow from areas of high pressure to areas of low pressure.he stronger the pressure difference, or pressure gradient, between a high-pressure system and a low pressure system, the stronger the wind. Sony VAIO VGN-SR94VS Battery The coriolis force caused by the Earth's rotation is what gives winds within high-pressure systems their clockwise circulation in the northern hemisphere (as the wind moves outward and is deflected right from the center of high pressure) and anticlockwise circulation in the southern hemisphere (as the wind moves outward and is deflected left from the center of high pressure). Sony VAIO VPC CW2MFX/PU Battery Friction with land slows down the wind flowing out of high-pressure systems and causes wind to flow more outward, or flowing more ageostrophically, from their centers. High pressure systems are frequently associated with light winds at the surface and subsidence through the lower portion of the troposphere. Sony VAIO VPC S11V9E/B Battery Subsidence will generally dry out an air mass by adiabatic, or compressional, heating.[8] Thus, high pressure typically brings clear skies.[9] During the day, since no clouds are present to reflect sunlight, there is more incoming shortwave solar radiation and temperatures rise. Sony VAIO VPCB119GJ/B Battery At night, the absence of clouds means that outgoing longwave radiation (i.e. heat energy from the surface) is not absorbed, giving cooler diurnal low temperatures in all seasons. When surface winds become light, the subsidence produced directly under a high-pressure system can lead to a build up of particulates in urban areas under the ridge, Sony VAIO VPCB11AGJ Battery leading to widespread haze.[10] If the low level relative humidity rises towards 100 percent overnight, fog can form.[11] Strong but vertically shallow high-pressure systems moving from higher latitudes to lower latitudes in the northern hemisphere are associated with continental arctic air masses.[12] Sony VAIO VPCB11AVJ Battery The low, sharp inversion can lead to areas of persistent stratocumulus or stratus cloud, colloquially known as anticyclonic gloom. The type of weather brought about by an anticyclone depends on its origin. For example, extensions of the Azores high pressure may bring about anticyclonic gloom during the winter, Sony VAIO VPCB11V9E Battery as they are warmed at the base and will trap moisture as they move over the warmer oceans. High pressures that build to the north and extend southwards will often bring clear weather. This is due to being cooled at the base (as opposed to warmed) which helps prevent clouds from forming. Sony VAIO VPCB11X9E Battery Once arctic air moves over an unfrozen ocean, the air mass modifies greatly over the warmer water and takes on the character of a maritime air mass, which reduces the strength of the high-pressure system.[13] When extremely cold air moves over relatively warm oceans, polar lows can develop.[14] Sony VAIO VPCCW18FJ/P Battery However, warm and moist (or maritime tropical) air masses which move poleward from tropical sources are slower to modify than arctic air masses. The circulation around mid-level ridges, and the subsidence at their center, act to steer tropical cyclones around their periphery. Sony VAIO VPCCW18FJ/R Battery Due to the subsidence within this type of system, a cap can be set up which inhibits the development of free convection. This limits thunderstorm activity near their center, and traps low-level pollutants such as ozone as hazeunder their base, which is a significant problem in large urban centers during summer months such as Los Angeles, California and Mexico City, Mexico. Sony VAIO VPCCW18FJ/W Battery The existence of an upper level ridge allows upper level divergence which leads to surface convergence. If a capping mid-level ridge does not exist, this leads to free convection and the development of showers and thunderstorms if the lower atmosphere is humid. Since tropical cyclones strengthen these ridges, Sony VAIO VPCCW19FJ/W Battery a positive feedback loop develops between the convective tropical cyclone and the upper level high, where the strength of both systems intensifies. This loop stops once ocean temperatures under the system cool sufficiently, under 26.5 °C (79.7 °F),[16] which forces the thunderstorm activity to wane, which then weakens the upper level ridge. Sony VAIO VPCCW1AFJ Battery When the subtropical butt ridge in the northwest Pacific is stronger than normal, it leads to a wet monsoon season for Asia.[17] The subtropical ridge position is linked to how far northward monsoon moisture and thunderstorms extend into the United States. Typically, the subtropical ridge across Sony VAIO VPCCW1AHJ Battery North America migrates far enough northward to begin monsoon conditions across the Desert Southwest from July to September.[18] When the subtropical ridge is farther north than normal towards the Four Corners, monsoon thunderstorms can spread northward into Arizona. Sony VAIO VPCCW1S1E Battery When suppressed to the south, the atmosphere dries out across the Desert Southwest, causing a break in the monsoon regime.[19] in the southern hemisphere in winter, the intensification of the mascaleni high brings moist air over the continent resulting into formation medium clouds thus lowering the day temperatures. Sony VAIO VPCCW1S1E/B Battery On weather maps, high-pressure centers are associated with the letter H in English,[20] or A in Spanish[21] (because alta is the Spanish word for high), within the isobar with the highest pressure value. On constant pressure upper level charts, anticyclones are located within the highest height line contour. Sony VAIO VPCCW1S1E/L Battery On Jupiter, there are two examples of an extraterrestrial anticyclonic storm; the Great Red Spot and the recently formedOval BA. Unlike any typical anticyclonic storm that happens on Earth when there is water, there's no water powering them. Instead, it is powered by smaller storms merging. Sony VAIO VGN-SR49VN/H Battery Another theory is that warmer gases rise in a column of cold air, creating a vortex. It is the case of other storms that include Anne's Spot on Saturn, and the Great Dark Spot on Neptune. In addition, anticyclones have been detected near the poles of Venus. Sony VAIO VGN-SR51B/P Battery,Sony VAIO VGN-SR51B/S Battery,Sony VAIO VGN-SR51MF Battery

No comments:

Post a Comment