An objectively defined three-dimensional cyclone phase space is proposed and explored. Cyclone phase is described using the parameters of storm-motion-relative thickness asymmetry (symmetric/nonfrontal versus asymmetric/frontal) and vertical derivative of horizontal height gradient (cold-versus warm-core structure via the thermal wind relationship). A cyclone's life cycle can be analyzed within this phase space, providing substantial insight into the cyclone structural evolution. An objective classification of cyclone phase is possible, unifying the basic structural description of tropical, extratropical, and hybrid cyclones into a continuum. Stereotypical symmetric warm-core (tropical cyclone) and asymmetric cold-core (extratropical cyclone) life cycles are illustrated using 1Њ Navy Operational Global Atmospheric Prediction System (NOGAPS) operational analyses and 2.5Њ NCEP-NCAR reanalyses. The transitions between cyclone phases are clearly illustrated within the phase space, including extratropical transition, subtropical and tropical transition, and the development of warm seclusions within extratropical cyclones. The planet's northwestern hemisphere inhabitance of the proposed phase space between 1980 and 1999 is examined using NCEP-NCAR 2.5Њ reanalyses. Despite the inability to adequately resolve tropical cyclones at the coarse 2.5Њ resolution, warm-core cyclones (primarily warm-seclusion extratropical cyclones) have a mean intensity that is 10 hPa lower than that of cold-core cyclones. Warm-core cyclones also have a much larger variability for intensity distribution, with an increased occurrence of lower MSLP. Further, at 2.5Њ resolution the lowest analyzed MSLP for a warm-core cyclone was 14 hPa lower than that for a cyclone that remains cold core. These results suggest that cyclones that maintain solely a cold-core structure (no warm-seclusion or tropical development) may be associated with a significantly weaker minimum observed intensity at 2.5Њ resolution, although further examination using higher-resolution data is required to refine this. Phase diagrams are being produced in real time to improve the forecasting of cyclone phase evolution and phase transitions, and to provide measures of phase predictability through ensembling of multiple models. The likelihood of warm-core development in cyclones can be anticipated by applying the diagnostics to various model forecasts, illuminating the potential for large intensity changes when the explicit model intensity forecasts may be insufficient.

A significant number of tropical cyclones move into the midlatitudes and transform into extratropical cyclones. This process is generally referred to as extratropical transition (ET). During ET a cyclone frequently produces intense rainfall and strong winds and has increased forward motion, so that such systems pose a serious threat to land and maritime activities. Changes in the structure of a system as it evolves from a tropical to an extratropical cyclone during ET necessitate changes in forecast strategies. In this paper a brief climatology of ET is given and the challenges associated with forecasting extratropical transition are described in terms of the forecast variables (track, intensity, surface winds, precipitation) and their impacts (flooding, bush fires, ocean response). The problems associated with the numerical prediction of ET are discussed. A comprehensive review of the current understanding of the processes involved in ET is presented. Classifications of extratropical transition are described and potential vorticity thinking is presented as an aid to understanding ET. Further sections discuss the interaction between a tropical cyclone and the midlatitude environment, the role of latent heat release, convection and the underlying surface in ET, the structural changes due to frontogenesis, the mechanisms responsible for precipitation, and the energy budget during ET. Finally, a summary of the future directions for research into ET is given.

A comprehensive climatology of extratropically transitioning tropical cyclones in the Atlantic basin is presented. Storm tracks and intensities over a period from 1899 to 1996 are examined. More detailed statistics are presented only for the most reliable period of record, beginning in 1950. Since 1950, 46% of Atlantic tropical cyclones transitioned to the extratropical phase. The coastal Atlantic areas most likely to be impacted by a transitioning tropical cyclone are the northeast United States and the Canadian Maritimes (1-2 storms per year), and western Europe (once every 1-2 yr). Extratropically transitioning tropical cyclones represent 50% of landfalling tropical cyclones on the east coasts of the United States and Canada, and the west coast of Europe, combined. The likelihood that a tropical cyclone will transition increases toward the second half of the tropical season, with October having the highest probability (50%) of transition. Atlantic transition occurs from 24Њ to 55ЊN, with a much higher frequency between the latitudes of 35Њ and 45ЊN. Transition occurs at lower latitudes at the beginning and end of the season, and at higher latitudes during the season peak (August-September). This seasonal cycle of transition location is the result of competing factors. The delayed warming of the Atlantic Ocean forces the location of transition northward late in the season, since the critical threshold for tropical development is pushed northward. Conversely, the climatologically favored region for baroclinic development expands southward late in the season, pinching off the oceanic surface area over which tropical development can occur. The relative positions of these two areas define the typical life cycle of a transitioning tropical cyclone: tropical intensification, tropical decay, extratropical transition and intensification, occlusion. Using a synthesis of National Hurricane Center Best-Track data and European Centre for Medium-Range Weather Forecasts reanalyses data, the intensity changes during and after transition are evaluated. It is extremely rare for a transitioning tropical cyclone to regain (in the extratropical phase) its peak (tropical phase) intensity. However, of the 61 transitioning tropical storms during the period 1979-93, 51% underwent post-transition intensification. Over 60% of cyclones that underwent post-transition intensification originated south of 20ЊN. In contrast, 90% of tropical cyclones that underwent post-transition decay originated north of 20ЊN. This suggests that strong baroclinic characteristics during formation are not necessary for strong post-transition development; in fact, they appear to hinder post-transition intensification and, therefore, the post-transition life span of the cyclone itself.

Fenestration of today is continuously being developed into the fenestration of tomorrow, hence offering a steadily increase of daylight and solar energy utilization and control, and at the same time providing a necessary climate screen with a satisfactory thermal comfort. Within this work a state-of-the-art market review of the best performing fenestration products has been carried out, along with an overview of possible future research opportunities for the fenestration industry. The focus of the market review was low thermal transmittance (Uvalue). The lowest centre-of-glass U g -values found was 0.28 W/(m 2 K) and 0.30 W/(m 2 K), which was from a suspended coating glazing product and an aerogel glazing product, respectively. However, the majority of high performance products found were triple glazed. The lowest frame U-value was 0.61 W/(m 2 K). Vacuum glazing, smart windows, solar cell glazing, window frames, self-cleaning glazing, low-emissivity coatings and spacers were also reviewed, thus also representing possibilities for controlling and harvesting the solar radiation energy. Currently, vacuum glazing, new spacer materials and solutions, electrochromic windows and aerogel glazing seem to have the largest potential for improving the thermal performance and daylight and solar properties in fenestration products. Aerogel glazing has the lowest potential U-values, ~ 0.1 W/(m 2 K), but requires further work to improve the visible transmittance. Electrochromic vaccum glazing and evacuated aerogel glazing are two vacuum related solutions which have a large potential. There may also be opportunities for completely new material innovations which could revolutionize the fenestration industry.

Forty-six percent of Atlantic tropical storms undergo a process of extratropical transition (ET) in which the storm evolves from a tropical cyclone to a baroclinic system. In this paper, the structural evolution of a base set of 61 Atlantic tropical cyclones that underwent extratropical transition between 1979 and 1993 is examined. Objective indicators for the onset and completion of transition are empirically determined using National Hurricane Center (NHC) best-track data, ECMWF 1.125Њ ϫ 1.125Њ reanalyses, and operational NCEP Aviation Model (AVN) and U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS) numerical analyses. An independent set of storms from 1998 to 2001 are used to provide a preliminary evaluation of the proposed onset and completion diagnostics. Extratropical transition onset is declared when the storm becomes consistently asymmetric, as measured by the 900-600-hPa thickness asymmetry centered on the storm track. Completion of the ET process is identified using a measure of the thermal wind over the same layer. These diagnostics are consistent with the definitions of tropical and baroclinic cyclones and are readily calculable using operational analyses. Comparisons of these objective measures of ET timing with more detailed three-dimensional analyses and NHC classifications show good agreement.

A 34-member ensemble-mean trajectory through the cyclone phase space (CPS) is calculated using Navy Operational Global Atmospheric Prediction System (NOGAPS) analyses for North Atlantic tropical cyclones (TCs) undergoing extratropical transition (ET). Synoptic composites at four ET milestones are examined: 24 h prior to the beginning of ET (TB − 24), the beginning of ET (TB), the end of ET (TE), and 24 h after the end of ET (TE + 24). While the extratropically transitioning TC structure is tightly constrained in its tropical phase, it has a variety of evolutions after TE. Partitioning the ensemble based upon post-ET intensity change or structure discriminates among statistically significant ET precursor conditions. Compositing the various post-ET intensity regimes provides insight into the important environmental factors governing post-ET development. A TC that intensifies (weakens) after TE begins transition (t = TB) with a negatively (positively) tilted trough 1000 km (1500 km) upstream. The negative tilt permits a contraction and intensification of the eddy potential vorticity (PV) flux, while the positive trough tilt prevents contraction and intensification of the forcing. In 6 of the 34 cases, the posttropical cold-core cyclone develops a warm-seclusion structure, rather than remaining cold core. Anticipation of this warm-seclusion evolution is critical since it represents a dramatically increased risk of middle- to high-latitude wind and wave damage. The warm-seclusion evolution is most favored when the scale of the interacting trough closely matches the scale of the transitioned TC, focusing the eddy PV flux in the outflow layer of the transitioning TC. The sensitivity of structural evolution prior to and after TE illustrated here gives insight into the degradation of global model midlatitude forecast accuracy during a pending ET event. Eliassen–Palm flux cross sections suggest that ET is primarily driven by the eddy angular momentum flux of the trough, rather than the eddy heat flux associated with the trough. The response of the transitioning TC to the eddy angular momentum forcing is to produce adiabatic ascent and cooling radially inward and beneath the region of the forcing to restore thermal wind balance. In the case of ET, the forcing is maximized lower in the atmosphere, and spread over much greater depth, than in the case of trough-induced TC intensification. Only after TE is the eddy heat flux forcing as significant as the eddy angular momentum forcing, further supporting a physical foundation for the CPS description of cyclone evolution.

Extratropical transition (ET) is the process by which a tropical cyclone, upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes, transforms into an extratropical cyclone. This process is influenced by, and influences, phenomena from the tropics to the midlatitudes and from the meso- to the planetary scales to extents that vary between individual events. Motivated in part by recent high-impact and/or extensively observed events such as North Atlantic Hurricane Sandy in 2012 and western North Pacific Typhoon Sinlaku in 2008, this review details advances in understanding and predicting ET since the publication of an earlier review in 2003. Methods for diagnosing ET in reanalysis, observational, and model-forecast datasets are discussed. New climatologies for the eastern North Pacific and southwest Indian Oceans are presented alongside updates to western North Pacific and North Atlantic Ocean climatologies. Advances in understanding and, in some cases, modeling the direct impacts of ET-related wind, waves, and precipitation are noted. Improved understanding of structural evolution throughout the transformation stage of ET fostered in large part by novel aircraft observations collected in several recent ET events is highlighted. Predictive skill for operational and numerical model ET-related forecasts is discussed along with environmental factors influencing posttransition cyclone structure and evolution. Operational ET forecast and analysis practices and challenges are detailed. In particular, some challenges of effective hazard communication for the evolving threats posed by a tropical cyclone during and after transition are introduced. This review concludes with recommendations for future work to further improve understanding, forecasts, and hazard communication.

The following study examines the position and intensity differences of tropical cyclones (TCs) among the Best-Track and five atmospheric reanalysis datasets to evaluate the degree to which reanalyses are appropriate for studying TCs. While significant differences are found in both reanalysis TC intensity and position, the representation of TC intensity within reanalyses is found to be most problematic owing to its underestimation beyond what can be attributed solely to the coarse grid resolution. Moreover, the mean life cycle of normalized TC intensity within reanalyses reveals an underestimation of both prepeak intensification rates as well as a delay in peak intensity relative to the Best-Track. These discrepancies between Best-Track and reanalysis TC intensity and position can further be described through correlations with such parameters as Best-Track TC age, Best-Track TC intensity, Best-Track TC location, and the extended Best-Track TC size. Specifically, TC position differences within the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), ECMWF Interim Re-Analysis (ERA-I), and Modern Era Retrospective-Analysis for Research and Applications (MERRA) exhibit statistically significant correlations (0.27 # R # 0.38) with the proximity of TCs to observation dense areas in the North Atlantic (NATL) and western North Pacific (WPAC). Reanalysis TC intensity is found to be most strongly correlated with Best-Track TC size (0.53 # R # 0.70 for maximum 10-m wind speed; 20.71 # R # 20.53 for minimum mean sea level pressure) while exhibiting smaller, yet significant, correlations with Best-Track TC age, Best-Track TC intensity, and Best-Track TC latitude. Of the three basins examined, the eastern North Pacific (EPAC) has the largest reanalysis TC position differences and weakest intensities possibly due to a relative dearth of observations, the strong nearby terrain gradient, and the movement of TCs away from the most observation dense portion of the basin over time. The smaller mean Best-Track size and shorter mean lifespan of Best-Track EPAC TCs may also yield weaker reanalysis TC intensities. Of the five reanalyses, the smaller position differences and stronger intensities found in the Climate Forecast System Reanalysis (CFSR) and Japanese 25-year Reanalysis (JRA-25) are attributed to the use of vortex relocation and TC wind profile retrievals, respectively. The discrepancies in TC position between the Best-Track and reanalyses combined with the muted magnitude of TC intensity and its partially nonphysical life cycle within reanalyses suggests that caution should be exercised when utilizing these datasets for studies that rely either on TC intensity (raw or normalized) or track. Finally, several cases of nonphysical TC structure also argue that further work is needed to improve TC representation while implying that studies focusing solely on TC intensity and track do not necessarily extend to other aspects of TC representation.