Search Results

You are looking at 1 - 10 of 28 items for

  • Author or Editor: John S. Daniel x
  • Refine by Access: All Content x
Clear All Modify Search
Susan Solomon and John S. Daniel

The technical achievements of Lewis and Clark have been celebrated in fields ranging from cartography to zoology. As America commemorates the bicentennial of their historic journey across the continent, this paper shows that their meteorological data and personal weather-related observations also are worthy of celebration. While the primary goal of the mission, as described by then-President Jefferson to the Congress, was economic and strategic, both Jefferson and cocaptains Lewis and Clark showed an interest in and capacity for scientific understanding of the meteorology of the then-unknown West. The seasonal evolution and variability of temperatures recorded for the first time by Lewis and Clark on the High Plains can now be shown to be quite close to average, thanks to many decades of collection of modern data by the U.S. Cooperative Observer Network stations along their route. While the diets, lives, and experiences of these early explorers and their men were profoundly different from those of modern Americans, the climate that they documented for the first time with care and accuracy remains familiar to us today.

Full access
Matthew S. Wandishin, John W. Nielsen-Gammon, and Daniel Keyser

Abstract

The process of tropopause folding is studied in the context of the life cycle of baroclinic waves. Previous studies of upper-level frontogenesis have emphasized the role of the vertical circulation in driving stratospheric air down into the midtroposphere. Here, a potential vorticity–based approach is adopted that focuses on the generation of a folded tropopause. To facilitate comparison of the two approaches, the diagnosis is applied to the upper-level front previously simulated and studied by Rotunno et al. The potential vorticity approach clarifies the primary role played by the horizontal nondivergent wind in producing a fold and explains why folding should be a common aspect of baroclinic development.

Between the trough and upstream ridge, prolonged subsidence within a region of weak system-relative flow generates a tropopause depression oriented at an angle to the large-scale flow. The large-scale vertical shear then locally increases the slope of the tropopause, eventually leading to a tropopause fold. In contrast, tropopause folding in the base of the trough is caused by the nondivergent cyclonic circulation associated with the surface thermal wave. The winds associated with the thermal wave amplify the potential vorticity wave aloft, and these winds, which decrease with height, rapidly generate a tropopause fold within the trough.

Full access
Daniel J. Vimont, John M. Wallace, and David S. Battisti

Abstract

Midlatitude atmospheric variability is identified as a particularly effective component of the stochastic forcing of ENSO. This forcing is realized via a seasonal footprinting mechanism (SFM), in which the tropical atmosphere is forced during the spring and summer by SST anomalies generated by midlatitude atmospheric variability during the previous winter. The strong relationship between the SFM and ENSO may serve to enhance ENSO predictability and supports the view that ENSO is linearly stable in nature.

Full access
Daniel P. Tyndall, John D. Horel, and Manuel S. F. V. de Pondeca

Abstract

A two-dimensional variational method is used to analyze 2-m air temperatures over a limited domain (4° latitude × 4° longitude) in order to evaluate approaches to examining the sensitivity of the temperature analysis to the specification of observation and background errors. This local surface analysis (LSA) utilizes the 1-h forecast from the Rapid Update Cycle (RUC) downscaled to a 5-km resolution terrain level for its background fields and observations obtained from the Meteorological Assimilation Data Ingest System.

The observation error variance as a function of broad network categories and the error variance and covariance of the downscaled 1-h RUC background fields are estimated using a sample of over 7 million 2-m air temperature observations in the continental United States collected during the period 8 May–7 June 2008. The ratio of observation to background error variance is found to be between 2 and 3. This ratio is likely even higher in mountainous regions where representativeness errors attributed to the observations are large.

The technique used to evaluate the sensitivity of the 2-m air temperature to the ratio of the observation and background error variance and background error length scales is illustrated over the Shenandoah Valley of Virginia for a particularly challenging case (0900 UTC 22 October 2007) when large horizontal temperature gradients were present in the mountainous regions as well as over two entire days (20 and 27 May 2009). Sets of data denial experiments in which observations are randomly and uniquely removed from each analysis are generated and evaluated. This method demonstrates the effects of overfitting the analysis to the observations.

Full access
Daniel P. Brown, John L. Beven, James L. Franklin, and Eric S. Blake

Abstract

The 2008 Atlantic hurricane season is summarized and the year’s tropical cyclones are described. Sixteen named storms formed in 2008. Of these, eight became hurricanes with five of them strengthening into major hurricanes (category 3 or higher on the Saffir–Simpson hurricane scale). There was also one tropical depression that did not attain tropical storm strength. These totals are above the long-term means of 11 named storms, 6 hurricanes, and 2 major hurricanes. The 2008 Atlantic basin tropical cyclones produced significant impacts from the Greater Antilles to the Turks and Caicos Islands as well as along portions of the U.S. Gulf Coast. Hurricanes Gustav, Ike, and Paloma hit Cuba, as did Tropical Storm Fay. Haiti was hit by Gustav and adversely affected by heavy rains from Fay, Ike, and Hanna. Paloma struck the Cayman Islands as a major hurricane, while Omar was a major hurricane when it passed near the northern Leeward Islands. Six consecutive cyclones hit the United States, including Hurricanes Dolly, Gustav, and Ike. The death toll from the Atlantic tropical cyclones is approximately 750.

A verification of National Hurricane Center official forecasts during 2008 is also presented. Official track forecasts set records for accuracy at all lead times from 12 to 120 h, and forecast skill was also at record levels for all lead times. Official intensity forecast errors in 2008 were below the previous 5-yr mean errors and set records at 72–120 h.

Full access
Hung-Neng S. Chin, Daniel J. Rodriguez, Richard T. Cederwall, Catherine C. Chuang, Allen S. Grossman, John J. Yio, Qiang Fu, and Mark A. Miller

Abstract

Using measurements from the Department of Energy’s Atmospheric Radiation Measurement Program, a modified ground-based remote sensing technique is developed and evaluated to study the impacts of the subadiabatic character of continental low-level stratiform clouds on microphysical properties and radiation budgets. Airborne measurements and millimeter-wavelength cloud radar data are used to validate retrieved microphysical properties of three stratus cloud systems occurring in the April 1994 and 1997 intensive observation periods at the Southern Great Plains site.

The addition of the observed cloud-top height into the Han and Westwater retrieval scheme eliminates the need to invoke the adiabatic assumption. Thus, the retrieved liquid water content (LWC) profile is represented as the product of an adiabatic LWC profile and a weighting function. Based on in situ measurements, two types of weighting functions are considered in this study: one is associated with a subadiabatic condition involving cloud-top entrainment mixing alone (type I) and the other accounts for both cloud-top entrainment mixing and drizzle effects (type II). The adiabatic cloud depth ratio (ACDR), defined as the ratio of the actual cloud depth to the one derived from the adiabatic assumption, is found to be a useful parameter for classifying the subadiabatic character of low-level stratiform clouds. The type I weighting function only exists in the lower ACDR regime, while the type II profile can appear for any adiabatic cloud depth ratio.

Results indicate that the subadiabatic character of low-level stratiform clouds has substantial impacts on radiative energy budgets, especially those in the shortwave, via the retrieved LWC distribution and its related effective radius profile of liquid water. Results also show that this subadiabatic character can act to stabilize the cloud deck by reducing the in-cloud radiative heating/cooling contrast. As a whole, these impacts strengthen as the subadiabatic character of low-level stratiform clouds increases.

Full access

A Focus On Mixed-Phase Clouds

The Status of Ground-Based Observational Methods

Matthew D. Shupe, John S. Daniel, Gijs de Boer, Edwin W. Eloranta, Pavlos Kollias, Charles N. Long, Edward P. Luke, David D. Turner, and Johannes Verlinde

The phase composition and microphysical structure of clouds define the manner in which they modulate atmospheric radiation and contribute to the hydrologic cycle. Issues regarding cloud phase partitioning and transformation come to bear directly in mixed-phase clouds, and have been difficult to address within current modeling frameworks. Ground-based, remote-sensing observations of mixed-phase clouds can contribute a significant body of knowledge with which to better understand, and thereby more accurately model, clouds and their phase-defining processes. Utilizing example observations from the Mixed-Phase Arctic Cloud Experiment (M-PACE), which occurred at the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program's Climate Research Facility in Barrow, Alaska, during autumn 2004, we review the current status of ground-based observation and retrieval methods used in characterizing the macrophysical, microphysical, radiative, and dynamical properties of stratiform mixed-phase clouds. In general, cloud phase, boundaries, ice properties, liquid water path, optical depth, and vertical velocity are available from a combination of active and passive sensors. Significant deficiencies exist in our ability to vertically characterize the liquid phase, to distinguish ice crystal habits, and to understand aerosol-cloud interactions. Further validation studies are needed to evaluate, improve, and expand our retrieval abilities in mixed-phase clouds.

Full access
Kenneth S. Gage, John R. McAfee, William G. Collins, Daniel Söderman, Horst Böttger, Alan Radford, and Ben Balsley

Wind profilers can provide useful wind data from remote regions of the globe, and incorporation of upper-level wind profiler data into analysis products can significantly improve the quality of analyses in data sparse regions.

A wind-profiling Doppler radar was installed by the Aeronomy Laboratory on Christmas Island during late 1985 as part of the Tropical Ocean Global Atmosphere (TOGA) Program. The Christmas Island profiler is self-contained and operates essentially unattended. Since April 1986, data from the Christmas Island profiler have been tele-metered via GOES Satellite to provide hourly-averaged soundings of the wind four times daily keyed to the standard synoptic observing times and incorporated routinely onto the Global Telecommunication System (GTS) for world-wide distribution.

In 1987 both NMC and ECMWF began using Christmas Island wind profiler observations in preparing their global analysis and forecast products. Detailed comparisons of NMC and ECMWF analyses with Christmas Island winds before and after profiler winds were introduced into the global analyses are presented. Results of statistical comparisons reveal a marked improvement in the analyses following the introduction of Christmas Island winds into the standard analysis products: before the Christmas Island winds were introduced into the analyses, monthly mean standard deviations between analyzed and observed winds were typically in the range 3–5 m · s−1 and monthly mean biases were typically in the range 1–3 m · s−1; after the Christmas Island winds were introduced, the standard deviation was reduced to about 1–2 m · s−1 at most heights, while the bias values were reduced to less than 0.5 m · s−1 at most heights.

Full access
John L. Beven II, Lixion A. Avila, Eric S. Blake, Daniel P. Brown, James L. Franklin, Richard D. Knabb, Richard J. Pasch, Jamie R. Rhome, and Stacy R. Stewart

Abstract

The 2005 Atlantic hurricane season was the most active of record. Twenty-eight storms occurred, including 27 tropical storms and one subtropical storm. Fifteen of the storms became hurricanes, and seven of these became major hurricanes. Additionally, there were two tropical depressions and one subtropical depression. Numerous records for single-season activity were set, including most storms, most hurricanes, and highest accumulated cyclone energy index. Five hurricanes and two tropical storms made landfall in the United States, including four major hurricanes. Eight other cyclones made landfall elsewhere in the basin, and five systems that did not make landfall nonetheless impacted land areas. The 2005 storms directly caused nearly 1700 deaths. This includes approximately 1500 in the United States from Hurricane Katrina—the deadliest U.S. hurricane since 1928. The storms also caused well over $100 billion in damages in the United States alone, making 2005 the costliest hurricane season of record.

Full access
Dan Bikos, Daniel T. Lindsey, Jason Otkin, Justin Sieglaff, Louie Grasso, Chris Siewert, James Correia Jr., Michael Coniglio, Robert Rabin, John S. Kain, and Scott Dembek

Abstract

Output from a real-time high-resolution numerical model is used to generate synthetic infrared satellite imagery. It is shown that this imagery helps to characterize model-simulated large-scale precursors to the formation of deep-convective storms as well as the subsequent development of storm systems. A strategy for using this imagery in the forecasting of severe convective weather is presented. This strategy involves comparing model-simulated precursors to their observed counterparts to help anticipate model errors in the timing and location of storm formation, while using the simulated storm evolution as guidance.

Full access