This paper examines the synoptic conditions that yield extreme precipitation in two regions with different orographic features, the Olympic Mountains and Puget Sound. To capture orographic extreme precipitation, a dynamical downscaling is performed, driven by the NCEP–NCAR reanalysis and evaluated for cool-season months from 1970 to 2010. Clustering techniques are applied to the regional climate simulation, which reveals the Olympic Mountains and Puget Sound as regions with distinct temporal variability in precipitation. Results show that approximately one-third of the extreme precipitation events in each region occur without a similarly extreme event in the other, in spite of the fact that the two areas are very closely located and one is downstream of the other. Composites of synoptic conditions for extreme precipitation events show differences in integrated vapor transport (IVT) due to its dynamical component (winds at 850 hPa) and its thermodynamical component [integrated water vapor (IWV)]. For Puget Sound events, IVT is lower compared to Olympic Mountain events because of lower wind speeds. Olympic Mountain events have lower IVT compared to events with extreme precipitation in both regions, but in this case, the difference is due to lower IWV and more southerly winds. These differences in the large-scale conditions promote differences in the mesoscale mechanisms that enhance precipitation in each location. For Puget Sound events, static stability is higher, and there is a weak rain shadow. For Olympic Mountain events, static stability is lower, and a strong rain shadow is present. During extreme events in both regions, orographic modulation is minimized and large-scale effects dominate.

Using 12years of high-resolution global lightning stroke data from the World Wide Lightning Location Network (WWLLN), we show that lightning density is enhanced by up to a factor of 2 directly over shipping lanes in the northeastern Indian Ocean and the South China Sea as compared to adjacent areas with similar climatological characteristics. The lightning enhancement is most prominent during the convectively active season, November-April for the Indian Ocean and April-December in the South China Sea, and has been detectable from at least 2005 to the present. We hypothesize that emissions of aerosol particles and precursors by maritime vessel traffic lead to a microphysical enhancement of convection and storm electrification in the region of the shipping lanes. These persistent localized anthropogenic perturbations to otherwise clean regions are a unique opportunity to more thoroughly understand the sensitivity of maritime deep convection and lightning to aerosol particles.Plain Language Summary Lightning results from strong storms lifting cloud drops up to high altitudes where freezing occurs and collisions between drops, graupel, and ice crystals lead to electrification. Thus, lightning is an indicator of storm intensity and sensitive to the microphysics of cloud drop formation, interactions, and freezing. We find that lightning is nearly twice as frequent directly over two of the world's busiest shipping lanes in the Indian Ocean and the South China Sea. The lightning enhancement maximizes along the same angular paths ships take along these routes and cannot be explained by meteorological factors, such as winds or the temperature structure of the atmosphere. We conclude that the lightning enhancement stems from aerosol particles emitted in the engine exhaust of ships traveling along these routes. These particles act as the nuclei on which cloud drops form and can change the vertical development of storms, allowing more cloud water to be transported to high altitudes, where electrification of the storm occurs to produce lightning. These shipping lanes are thus an ongoing experiment on how human activities that lead to airborne particulate matter pollution can perturb storm intensity and lightning.

Abstract Our coasts are a critical intersection of ecological, social, and economic interests. They are the breeding ground for aquatic plants and animals, the playground for residents and tourists, and the launching ground for shipping, fishing, and resource development projects. In arctic regions, these areas are generally poorly characterized (often due to their sheer size, sparse population and inaccessibility), yet are perhaps the most fragile environment. As such, the arctic coast is particularly vulnerable to the impacts of human activity - particularly accidental chemical spills. Reducing the risk of and/or responding to emergency situations requires a thorough understanding of both the coastal environment, adjacent submerged lands and often the jurisdictional boundaries of stakeholders. In most cases, this effort begins with a mapping program that identifies the land/seabed boundaries and usage, and provides adequate charting for over-water emergency response activities. These observations must be regularly repeated to track ongoing coastal and ecological processes as well as the impacts from episodic events. Whereas small, local site investigations are typically best performed from vessel-mounted sensors, aerial remote sensing techniques are often well suited for regional-scale mapping programs.

Seafloor Surface Investigation Many geohazards are visible on the seafloor surface due to their geomorphic expression. These surface expressions can be viewed using sonar imaging and/or multibeam Coastal zones are among the most challenging locations to juggle the delicate balance of infrastructure development, consideration for the environment, and economic requirements related to the collection and analysis of data necessary for hazard assessments and mitigation during design. This consideration is not limited to sustainability of the environment (such as the local ecosystems) but also resiliency. Geological conditions are often a critical factor in resilient infrastructure development along the coast, yet they are frequently difficult to study. The geological conditions that present hazards to infrastructure are known as geohazards, which in the coastal zone may include examples such as nearshore earthquakes, unstable ground and inundation. With the number of existing as well as new projects planned within coastal zones, the need for properly identifying geohazards associated with a given project site becomes critical for cost-effective construction and sustained operation throughout their designed life. The cohesive integration of these techniques—bathymetry, imagery, geophysics and geotechnics—play an integral role in the evaluation of marine geohazards affecting the design, construction and longterm reliability of coastal infrastructure. Here, we describe a modern approach to geohazard investigations in the coastal environment that incorporates technology developed recently, which has revolutionized some aspects of data collection and provide solutions that are now within the economic reach of coastal infrastructure projects. We will focus on investigations that are below Investigations of Marine Geohazards For Coastal Infrastructure Projects

Application of the method of partial least squares (PLS) regression to geophysical data is illustrated with two cases: (1) finding sea level pressure patterns over the North Pacific associated with dynamically‐induced winter‐to‐winter variations in snowpack in the Cascade mountains of western Washington state and (2) finding patterns of sea surface temperature over the tropical oceans that modulate Atlantic hurricane activity on a year‐to‐year basis. In both examples two robust patterns in the “predictor field” are identified that, in combination, account for over half the variance in the target time series.

The timing of the onset of coastal upwelling in spring and its intensity over the upwelling season are critical factors in the productivity and structure of the California Current ecosystem (CCE). We use an index of coastal upwelling to characterize physical forcing over the latitudinal extent of the CCE, and compare the evolution of the upwelling season in 2005 with previous years. The onset of coastal upwelling in 2005 in the northern California Current was delayed by 2–3 months. Upwelling was stronger than normal in the latter part of the upwelling season, allowing the cumulative upwelling to reach the climatological mean by fall. Although physical conditions were unusual in 2005, they were not unprecedented in the historical record. However, the timing and strength of coastal upwelling is a critical ecological factor, particularly for species whose life histories are closely tuned to the annual cycle. The unusual physical and biological conditions observed in spring 2005 illustrate the sensitivity of the CCE to possible future climate extremes.

Since the mid-1970s, large-scale episodic events such as disease epidemics, mass mortalities, harmful algal blooms and other population explosions have been occurring in marine environments at an historically unprecedented rate. The variety of organisms involved (host, pathogens and other opportunists) and the absolute number of episodes have also increased during this period. Are these changes coincidental? Between 1972 and 1976, a global climate regime shift took place, and it is manifest most clearly by a change in strength of the North Pacific and North Atlantic pressure systems. Consequences of this regime shift are: (1) prolonged drought conditions in the Sahel region of Africa; (2) increased dust supply to the global atmosphere, by a factor of approximately four; (3) increased easterly trade winds across the Atlantic; (4) increased eolian transport of dust to the Atlantic and Caribbean basins; and (5) increased deposition of iron-rich eolian dust to typically iron-poor marine regions. On the basis of well-documented climate and dust observations and the widely accepted increase in marine outbreak rates, this paper proposes that the increased iron supply has altered the micronutrient factors limiting growth of opportunistic organisms and virulence of pathogenic microbes, particularly in macronutrient-rich coastal systems.

Improved observations in the tropical Pacific during the Tropical Ocean‐Global Atmosphere (TOGA) program have served to corroborate preexisting notions concerning the seasonally dependent relationships between sea surface temperature, sea level pressure, wind stress, rainfall, upper tropospheric circulation, and ocean thermal structure anomalies in the El Niño‐Southern Oscillation (ENSO) phenomenon. However, the paradigm of a quasiperiodic “ENSO cycle,” phase locked with the annual march, does not capture the complexity of the evolution of the anomalies. The inadequacy of this model was particularly apparent during the second half of TOGA when the variability was highly aperiodic. Also, a single modal structure or empirical orthogonal function does not appear to be capable of representing the range of spatial patterns of ocean‐atmosphere interaction in the tropical Pacific. These results suggest the need for a more inclusive phenomenological description of ENSO. Data collected during TOGA serve to confirm the influence of tropical Atlantic sea surface temperature anomalies upon rainfall in northeast Brazil.

Rotated principal component (RPC) analysis, subject to the varimax criterion and including area weighting, is applied to a 58-yr record (1931-88) of monthly-and seasonal-mean Climatic Division precipitation anomalies for the contiguous United States to document wintertime precipitation variability in the region of California. Rotated principal components (time series) derived from this analysis are related to anomalies of seasonal-mean global sea surface temperature, and monthly mean Northern Hemisphere 500-hPa geopotential height and sea level pressure (SLP).Wintertime seasonal-mean precipitation in California is captured by two RPCs. The first RPC documents coherent precipitation anomalies centered in northern California, Oregon, southern Idaho, and eastern Washington, and explains the largest portion of area-averaged variance of any of the patterns in the decomposition. A second RPC captures coherent precipitation variability in the south coast and southeast desert regions of California, southern Nevada, southern Utah, and northern Arizona. Fluctuations in the first RPC correlate poorly with Pacific Ocean SST anomalies. However, wet winters in the region of the second RPC correlate modestly with simultaneous cool western subtropical Pacific Ocean SST anomalies and weakly with warm SST anomalies over a broad region of the central and eastern tropical Pacific. The spatial scale of the tropical SST correlations and the prominent multidecadal timescale signal of the RPC are consistent with ENSO fluctuations on this timescale influencing southern California precipitation.Consistent with the results of earlier studies, significant correlations are found between California wintertime monthly mean precipitation variability and regional 500-hPa geopotential height and SLP anomalies. Linear regression analysis is used to construct estimates of the total 500-hPa geopotential height and SLP fields (climatology plus anomaly) that are representative of the extreme wet and dry California winter months; these are then compared with the observed conditions in the individual extreme months. Several different Bow patterns appear capable of producing anomalously large monthly precipitation totals in California.

ENSO-related seasonal-to-interannual variability in the Pacific basin is documented, based on marine surface observations of monthly mean sea surface temperature, sea level pressure, and wind, together with satellite-based estimates of rainfall and mean tropospheric temperature. Anomalies in these fields are linearly regressed onto simultaneous values of an index of equatorial Pacific SST anomalies. The analysis is performed separately on the data for earlier (1950-78) and later (1979-92) epochs of the record. The analyses are further stratified in terms of the climatological-mean warm and cold seasons in the equatorial Pacific, which correspond to January-May and July-November, respectively. Composite SST, wind, and rainfall fields for the warm and cold seasons that fall within typical warm and cold ENSO episodes are also presented.Despite the dramatic differences in the sequencing of ENSO warm episodes with respect to the annual march in the two epochs, the anomaly patterns are found to be remarkably similar and generally consistent with the Rasmusson and Carpenter composite. SST and zonal wind anomalies were quite comparable in strength in the warm and cold seasons, although the distributions were somewhat different. Rainfall anomalies and the associated anomalies in surface wind convergence and mean tropospheric temperature were much stronger during the warm season (and particularly during January-February) than during the cold season. Some aspects of the observed rainfall anomaly seasonality can be explained on the basis of simple thermodynamical considerations.

The coupled atmosphere-ocean system in the equatorial eastern Pacific and Atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes. The contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt. The March equinox corresponds to the warm season when the equatorial cold tongues in the eastern Pacific and Atlantic are absent. With the onset of summer monsoon convection over Colombia, Central America, and West Africa in May-June, northward surface winds strengthen over the eastern Pacific and Atlantic, the equatorial cold tongues reappear, and the marine convection shifts from the equatorial belt to the intertropical convergence zones (ITCZs) along 8-degrees-N. As the northern summer progresses, the ITCZs remain strong and shift northward to near 10-degrees-N, while sea surface temperature (SST) continues to drop over the cold tongues and the southern tropics, perhaps in response to the expanding stratocumulus cloud decks in the latter region. The cold tongue-ITCZ complex persists through the September equinox, which is characterized by suppressed convection, not only over the cold tongues, but also over much of equatorial South America.On the basis of observational evidence concerning the timing and year-to-year regularity of the surface wind changes during the development of the cold tongues, it is argued that 1) the increase in the northward surface winds in response to the onset of the northern summer monsoon may be instrumental in reestablishing the cold tongues, and 2) positive feedbacks involving both the zonal and meridional wind components contribute to the remarkable robustness of the cold tongue-ITCZ complexes in both oceans.

Temporal correlations between near-equatorial surface wind and sea-surface temperatures (SST) at 11°W in the eastern Pacific Ocean are investigated using data from an array of moored sensors between 5°N and 5°S. The signature of tropical instability waves with periods of 20–30 days is apparent in time series of SST and both the meridional and zonal wind components. Results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional SST gradient (equatorial front) normally located just north of the equator. Perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds. Evidence of the air-sea coupling is stronger in time series of the meridional gradients of wind and SST than between time series of the variables themselves. The meridional differencing serves as a high-pass filter in the space domain, which removes planetary-scale wind fluctuations that are unrelated to the local SST perturbations. The wind fluctuations observed in association with tropical instability waves are on the order of 1–2 m s−1. These results indicate that SST variability on weekly to monthly time scales forces perturbations in the surface wind field. It is suggested that the principal coupling mechanism in this region is the modification of the atmospheric boundary layer stratification. Over the equatorial cold SST tongue the vertical wind shear within the lowest 100 m of the atmosphere is strong and the surface winds are conspicuously weak. As the air flows northward across the equatorial front the boundary layer becomes destabilized, momentum is mixed downward, and the surface winds increase.

Relationships among the atmospheric phenomena associated with the Southern Oscillation and El Nino are investigated, using the Comprehensive Ocean-Atmosphere Data Set (COADS) of marine surface observations from ships of opportunity and the World Monthly Surface [Land] Station Climatology (WMSSC) for the period 1950-79. Annual mean (April March) sea level pressure at Darwin, Australia is used as an index of the Southern Oscillation. Results are based on simple linear correlation techniques, stratified by season as in the Rasmusson and Carpenter (1982) composite.Correlations on the order of +0.9 are observed between Darwin pressure, sea surface temperature (SST) and rainfall in the equatorial central Pacific, and zonal wind in the equatorial western Pacific. Relations among these variables are strongest from July through November, when the month to month autocorrelation is also at its strongest. Sea surface temperature along the Peruvian coast and pressure in the eastern Pacific are also most strongly coupled to the Southern Oscillation during these months, which correspond to the cool season in that region.The amplitude of the tropical pressure and central Pacific SST anomalies associated with the Southern Oscillation appear to be just as large and the relationships between them just as coherent during positive excursions of the Southern Oscillation (cold episodes) as during negative excursions (warm episodes).Lead/lag relationships among climatic variables associated with the Southern Oscillation and El Nino events along the South American coast are also examined in the context of the same seasonal stratification. Our results are generally consistent with the traditional view that the Southern Oscillation is, to first order, a standing oscillation with geographically fixed nodes and antinodes.