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TAMDAR Project: Report on the potential value of TAMDAR observations

 

TAMDAR Project (Tropospheric Airborne Meteorological Data Reports)

-Purpose of this report:

This report fulfills the renegotiated Task 8 of FSL's TAMDAR project work for FY2001.

Task 8, "to assess the potential of [TAMDAR] to reveal relevant atmospheric features not now routinely observed" can be started even in the absence of TAMDAR data. We now anticipate a literature search for cases in which research aircraft have collected humidity (and turbulence) data in connection with field projects to study mesoscale weather features. From field project research, we hope to extrapolate some of the gains to be expected from TAMDAR data. As described in our project plan, we believe we can "look particularly at the potential for low-altitude, high temporal resolution humidity information from [TAMDAR] to improve our understanding of, and ability to forecast, convective weather."

This page has been assembled by Ed Szoke of the NOAA Forecast Systems Laboratory. You can view my homepage here.

-Literature Review

    Overview

Research aircraft have been a crucial part of many field programs to help further the understanding of many areas of meteorology, from convective storms and boundary layer fair weather structure to powerful oceanic winter storms. This report highlites some aircraft findings for a broad sampling of such studies over the past 25 years, with emphasis, as stated in Task 8, on the moisture structure identified by the aircraft data. Turbulence structure is also noted, either by direct measurements of turbulence, or more often by measurements of vertical velocity by the aircraft.

    Structure within synoptic-scale storm systems: Oceanic storms.

There have been a number of field experiments where research aircraft have made a major contribution to diagnosing the structure of organized storm systems, ranging from winter cyclones in the central U.S. to oceanic cyclones in the Pacific and Atlantic. A workhorse aircraft for these purposes has been the NOAA P-3 aircraft, and typically the dropsondes deployed from these aircraft have been emphasized by many of these studies as they have enabled a more complete picture of the systems being studied to be diagnosed. For the purposes of this report we will highlight some examples of flight level aircraft data from the various studies, organized by the research programs below. A good overview of much of this material can be found in "Fronts, Jet Streams and the Tropopause" by Shapiro and Keyser, which is Chapter 10 of "Extratropical Cyclones" (AMS, 1990).

    OCEAN STORMS field experiment (Eastern Pacific, 1987)

One of the systems studied during this program was a cold front approaching the Pacific Northwest on two consecutive days, 9 and 10 Dec 1987. Extensive use of the P-3 was made to study this relatively typical cold front which trailed south from an oceanic storm in the Gulf of Alaska. In fact, the study focused on a stalled part of the front that was positioned WSW to ENE offshore and did not have much if any precipitation associated with it. In terms of moisture, the aircraft flight on 10 Dec revealed that high levels of relative humidity were confined to a narrow band along the sloping frontal surface (see Fig. 14) from the paper by Bond and Shapiro (1991)), even though the satellite image indicated a nondescript broad band of cloudiness. (Note that the cross-section in Fig. 14 was constructed from aircraft flight level data only, and goes across the front as shown in their this figure.)

A very interesting aspect of this study came from several aircraft passes across the front at three altitudes below 2000 m AGL. Their Fig. 18 shows how narrow (under 2 km in width) the main updraft (and therefore likely the main turbulence at this level) was within this synoptic scale front. This shows the potential for aircraft data to diagnose mesoscale structure within what appears to be a fairly broad synoptic-scale cold front.

    ERICA field experiment: Atlantic Ocean, winter of 1988/89

A major field experiment, the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) was conducted during the winter of 1988 to 89 and resulted in a number of papers that used research aircraft to document mesoscale structures and features within Atlantic cyclones.

    Raga et al. (1994) examined the precipitation bands within a relatively typical winter cyclone (as shown in their Fig. 1). A key figure from their paper that shows the fine scale structure as the aircraft crossed the cold front at an altitude of 300 m AGL is their Fig. 3. This figure (along the cross-section shown in their Figure 1) shows very concentrated up and downdrafts (and by inference turbulence) and significant moisture changes over a 6 to 12 km scale across the cold front.

    A study of another storm during ERICA on 4 January 1989 by Neiman et al. (1993) extensively used the NOAA P-3 aircraft to document a very complex structure to this system, as shown in their analyses at the 350 m AGL level. A times series of more of the actual aircraft data through the eastern cold front (at the southernmost pass shown in the above figure) is displayed in their Fig. 10. A strong gradient in moisture (through the variable equivalent potential temperature) is present in a short distance across the frontal zone at the 350 m AGL level. They note the highly turbulent nature (through the vertical velocity plot) in both the pre- and post-cold frontal marine boundary layer (p. 2184 of their article).

    Another look at the same 4 January 1989 storm was presented by Liu et al. (1997). Their Fig. 3 shows a closeup of the frontal structure just north of the aircraft track shown in the study by Nieman et al. overlaid with radar reflectivity from the radar aboard the aircraft. A larger view that shows the flight level (~300 m AGL) data in a circumference around the storm is shown by their Fig. 14. Such a figure illustrates how even aircraft tracks across a storm at just a few different angles could likely supply useful data for enhancing an analysis of the mesoscale structure of a storm system.

    Another ERICA storm on 19 January 1989 is summarized in an article by Blier et al. (1995). An overview of the system is shown at a flight level of about 300 m AGL in Fig. 13 of Blier et al. (1995), showing the complex mesoscale frontal structure of this cyclone. Their Fig. 10 presents a set of aircraft traces for different variable for three separate legs, again at about 300 m AGL. Crossings of the cold fronts as well as the "bent-back" warm front are shown on these traces, with sharp demarcations in the variables, as well as some fairly turbulent looking structure (for example behind the cold front), even though vertical velocity is not shown in these particular traces.

    COAST experiment - Eastern Pacific, 1993 and 1995

The Coastal Observation and Simulation with Topography (COAST) experiment studied Eastern Pacific Ocean cyclones with the NOAA P-3 aircraft during two separate early winter seasons of 1993 and 1995.

    The cold front approaching the Washington coast on 3 December 1993 was the focus of a study by Chien et al. (2001). The cold front was extenively studied by a number of passes of the P-3 at several different altitudes, as shown by their Fig. 13. Aircraft data from a pass across the cold front at a higher altitude then some of the Atlantic studies, 1500 m AGL, is shown in their Fig. 9. This figure shows that the aircraft data was able to document a very interesting frontal structure at this higher level, with a frontal zone about 36 km wide that consisted of two distinct transitions. Note the 5 m/s updraft they encountered ahead of the first transition, showing the very turbulent structure, at smaller scales, ahead of the frontal zone. About 30 min after this data was taken the P-3 made another flight across the frontal zone at 1500 m, this time heading NW, as shown in their Fig. 10. On this leg even stronger updrafts and downdrafts were found. They commented in their article that at lower elevations the front was sharper, as found in the ERICA passes at 300 m AGL.

    A storm during the second phase of COAST on 9-10 December 1995 was the focus of a study by Doyle and Bond (2001), this time concentrating on the warm frontal structure. The approaching system and its associated warm front is shown in their Fig. 4. A cross-section through the warm front showing the aircraft passes and analysis is presented in their Fig. 7, with a pass through a different portion of the warm front and a similar analysis shown in their Fig. 10. An interesting aspect of their study was, as they noted, that it offered a rare opportunity to document the turbulence that occurred in various sectors of the front and the nearshore flow. The actual aircraft time series of vertical velocity for passes through three distinct areas of the storm at the lower altitudes is shown in their Fig. 16. They calculated the TKE from this data and noted the different turbulence characteristics and intensities in each zone.

    Structure within synoptic-scale storm systems: Continental storms.

A couple of field programs are discussed below where aircraft data were used to study continental storm systems.

    Frontal systems over the continental U.S.: STORMFEST, 1992.

The Stormscale Operational and Research Meteorology-Fronts Experiment Systems Test (STORM-FEST) field program was a major undertaking to study storms and frontal systems over the central United States, carried out during February and March of 1992. A couple of studies from this field program that highlighted aircraft measured data are discussed below.

    One of the stronger storm systems that occurred during STORMFEST emerged from Colorado on 8 March and then traversed across the central U.S. over the next two days. The two studies below discuss different aspects of this system.

      Neiman et al. (1998) studied this system and present a number of analyses for different stages of the storm and its attendant frontal system. Many of these analyses involve mainly special sounding data rather than aircraft flight data (like would be obtainable from TAMDAR), so are not shown here. They do present on analysis during the later stages of the storm (along the line D' to D'' shown in their Fig. 6e) that combines sounding data with aircraft flight level data in their Fig. 14. Note that the horizontal scale of this figure is quite large, going from eastern Colorado east to Georgia. The main point to be made is the structure shown within the two fronts, and within the jet, are made possible with the aircraft measurements.

      The study by Miller et al. (1996) concentrated on the structure of the arctic front as it passed through a dense array of surface stations and other observing systems near Kansas City. During the time they studied the front it was typical of a strong arctic cold front moving across the mid-section of the country. There was actually no precipitation with the front, but extensive low cloudiness behind it as shown in this visible satellite image from their paper. A number of aircraft legs across the front below 1.6 km AGL using the NCAR King Air airplane where made, and two cross-sections for different times are presented in their Fig. 22 and Fig. 23. Both the moisture structure and the wind flow derived from the aircraft (and other) data are depicted, showing both the main updraft along the leading edge of the front but then interesting up and down motions well behind the front at the top fo the shallow cold air.

    Frontal systems over the continental U.S. during the summer: VORTEX studies.

Although VORTEX (Verification of the Origins of Rotation in Tornadoes Experiment) was designed to investigate the cause of rotation in supercell storms and tornadoes, a couple of studies used the facilities available (including the NOAA P-3 aircraft) to study frontal systems that occurred during the spring 1995 program centered over the Oklahoma area (but extending to nearby regions as needed).

    Neiman and Wakimoto (1999) studied a Pacific cold front as it emerged onto the Southern Plains and interacted with a shallow cold airmass that was in place at lower elevations. There was nothing unusually dramatic about this event, instead it was typical of this kind of interaction that occurs as frontal systems emerge from the Rockies in the springtime, so represents what might be expected from aircraft data with a typical weather system. An overview of the frontal systems is shown in their Fig. 3. An aircraft pass with the NOAA P-3 across the frontal zone and into the cooler "arctic" air at a flight level of ~200 m AGL is shown in their Fig. 17. This flight documents the very sharp gradient in temperature and humidity as the aircraft penetrated into the cooler airmass, but also shows a very interesting sharp jump in up and down motion as "the aircraft observed a density-current-like wake region within the Arctic air". A similar aircraft leg, this time heading west at ~275 m AGL (their Fig. 20), shows very complex and turbulent structures as the aircraft passed through the various mesoscale airmasses. A third pass is presented in their Fig. 23 which shows an eastward heading pass at an altitude of ~750 m AGL across the Pacific front, dryline and then into the cooler air. Note the considerable amount of vertical motion found between the front and the dryline at this level. This study provides a nice example of the details and structure that can be revealed by aircraft data for a fairly typical weather event.

    A typical dryline setup on 6 May 1995 was studied by Atkins et al. (1998), using aircraft data from both the NOAA P-3 and the NCAR Electra. An image of the radar fineline associated with the dryline as well as the convective rolls east of it, overlaid with aircraft data, is shown in their Fig. 3. A NOAA P-3 aircraft pass at 900 m AGL across the convective rolls reveals substantial changes in moisture and vertical motion on 10 km scales. Considerable variation in moisture and other variables along the dryline was detected by the NCAR Electra in its pass at ~330 m as shown by their Fig. 9. Finally, two additional passes across the dryline by the NOAA P-3 at a lower elevation of 150 m AGL are shown in their Fig. 18, depicting an extremely sharp and large gradient of moisture across the dryline.

    Convective season weather and convective storm systems.

Convective weather, from the storm scale to organized convective systems, has been the focus of a number of research studies that utilized aircraft data. A sampling of these studies is given below.

    CCOPE, High Plains, June-August 1981.

The Cooperative Convective Precipitation Experiment (CCOPE) was a comprehensive field experiment held in eastern Montana during the summer of 1981 that used a wide variety of observing systems to investigate convection on many scales. A variety of research aircraft was used, including a storm-penetrating T-28, the high altitude NCAR Sabreliner, and Queen and King Air Aircraft.

    A variety of organized convective systems were observed during CCOPE, but the study by Fanhauser et al. (1992) examined a relatively typical and somewhat weak line on 20 June 1981. Their paper presents low-level aircraft data from crossings of the squall line, as well as flights along the inflow near the updraft for a portion of the line. An example of the later flight is shown in Fig. 8 from their paper, showing the aircraft wind, temperature and moisture data overlaid with radar imagery for a flight above the squall line's outflow layer at about 700 m AGL.

    CINDE, Eastern Colorado, June-August 1987.

The Convective Initiation and Downburst Excperiment (CINDE) was conducted along the Front Range of the Rocky Mountains near the Denver, Colorado area from 22 June to 7 August 1987. It was designed to study a variety of boundary layer and convective features, but especially to further try to understand the causes of convective initiation by boundaries and other factors. One important boundary know to occur in the area is locally called the Denver Cyclone, and was the focus of the study below.

    17 July 1987 was a Denver Cyclone day and well-studied with the CINDE observational array and aircraft. An analysis of the Denver Cyclone near the time of the aircraft flights (1500 MDT) is shown in Fig. 5b from the paper by Wilson et al. (1992). Aircraft flights across the convergence zone associated with the Denver Cyclone feature were made by the University of North Dakota's Citation at ~0.4 km AGL and the NCAR King Air at ~0.9 km AGL as shown in their Fig. 13. Some of the actual aircraft flight level data is shown in their Fig. 14, which depicts plots of both moisture and vertical velocity, both of which show sharp changes near the quasi-stationary convergence zone. The importance of such a near-stationary low-level convergence boundary on potential convective development is nicely shown by Fig. 16, which illustrates how moisture is not only greater along the boundary but also extends upwards to higher levels, forced upwards over time by the sustained low-level convergence and upward motion, creating an environment more conducive to convection. In particular Fig. 16c shows the two aircraft passes overlaid, and this illustrates how such aircraft measurements could add considerable detail to determining the moisture structure of such a mesoscale boundary layer feature.

    CaPE, Florida, July-August 1991.

A somewhat similar type of program called the Convection and Precipitation/Electrification (CaPE) experiment was held in eastern Florida centered near Cape Canaveral during the summer of 1991. As with CINDE, an extensive observational network was in place for this study. Two papers showing the importance of aircraft data for CaPE studies are given below.

    The sea breeze front, like the Denver Cyclone in eastern Colorado, is a low-level boundary that has a major influence on subsequent convective development in Florida. The study by Atkins et al. (1995) examined two August sea breeze events during CaPE. Aircraft data from a pass by the Wyoming King Air at about 0.5 km AGL across the sea breeze front on 6 Aug 1991 is shown in their Fig. 18. For this case the aircraft data showed an interesting zone between the true surface wind shift line and the rise in moisture and drop in temperature, which they called the "thermodynamic frontal zone", apparently caused by a vertical circulation along the sea breeze front. They also documented radar fine lines ahead of the sea breeze front called horizontal convective rolls, which the next study details.

    The importance of horizontal convective rolls in the boundary layer and how they can act much like other low-level convergence boundaries in setting up a local or mesoscale environment more conducive to convection is the subject of a CaPE study by Weckworth et al. (1996). The horizontal convective rolls appear in visible satellite imagery as cloud streets of cumulus with spacing in the Florida summer environment of about 2 to 4 km. Aircraft data from the King Air research aircraft of NCAR and Wyoming are shown in their Fig. 6 for two different days, with passes at a couple of levels in or near the boundary layer (which topped out around 1 km AGL). The aircraft data nicely shows considerable turbulence structure (through the vertical velocity variations) across the rolls, as well as organized higher levels of moisture where each roll was located.

    Wintertime boundary layer features.

We conclude with some research aircraft measurements of boundary layer features such as boundary layer rolls and the Denver Cyclone, but in a winter environment. Three different studies are shown in the examples below.

    Labrador Sea Deep Convection Experiment, Winter, 1987.

This smaller experiment employed two C-130 aircraft of the U.S. Air Force Reserve 53d Squadron-the "Hurricane Hunters" to investigate the air-sea interaction during an extreme cold-air outbreak.

    The cold-air outbreak of 8 February 1987 was discussed in the paper by Renfrew and Moore (1999). A visible satellite image nicely shows the streets at about 4 to 6 km spacing, with the aircraft crossing positions indicated on the image. The aircraft data at 170 m showed little variation in temperature across the rolls, but like the CaPE study it showed large variations in moisture.

    Lake Effect Snow Studies (LESS) program, Winter 1984, Lake Michigan.

LESS was a earlier study concentrating on snowbands during cold-air outbreaks over Lake Michigan.

    The 10 January 1984 cold-air outbreak was the focus of the paper by Agee and Gilbert (1989) which used data from the NCAR King Air and Queen Air aircraft. The five flight levels used are shown in their Fig. 8 , with the data summarized in their Fig. 11 to show the wide variations in the moisture distribution. The very turbulent nature of the flow at the highest flight level (around 1400 m MSL) is shown from their Fig. 13.

    Winter Icing and Storms Project, Winter 1990, Eastern Colorado.

The Winter Icing and Storms Project (WISP) was held in eastern Colorado during February and March of 1990 to further the understanding of the processes leading to the formation and depletion of supercooled liquid water in winter storms, with the goal to improve forecasts of aircraft icing. WISP featured many research observations from a variety of sensors and research aircraft. The study below was a fairly complete study of a rather complex event.

    Rasmussen et al. (1995) studied the Valentine's Day storm, which began as an arctic outbreak with a shallow upslope cloud layer forming that contained supercooled liquid water, then evolved into a complex storm system with a heavy mesoscale snowband resulting from low-level forcing associated with a Denver Cyclone. A collection of cross-sections derived primarily from the aircraft data show the complexity of this storm system, including the large fluctuations in moisture over small layers and distances. Their Fig. 18 presents more aircraft data that further show the large variations of supercooled liquid water in the vertical in the low overcast situation. Aircraft data taken later across the period of the snowband is depicted in their Fig. 25. This data reveal the small-scale horizontal scale of this snowband that produced over a 8 inches of snow in a narrow swath.

-Summary

The above studies are a sampling of some of the research projects that have used research aircraft to help diagnose mesoscale and smaller structures in a variety of weather systems, from the fair-weather boundary layer to strong synoptic storms. While it is true that during such programs the aircraft are directed in such a way to make strategic crossings across features that in many cases commercial aircraft would tend to avoid, in many of the studies the weather systems are relatively typical and so would likely be penetrated at various levels and locations by commercial aircraft. Although the aircraft data is its own right would be useful for weather analysis by a forecaster, much as aircraft ascent and descent soundings are used today, a key to getting the most out of such data, which would be rather randomly spaced and not as targeted or organized as in a research program, would be to have it as input to an analysis package that can blend this key data with all other types of weather information, such as the Local Analysis and Prediction System (McGinley, 1991). Using such a system as LAPS on a small enough scale, and then potentially as input to a similarly-scaled numerical model, would likely provide the most input for this unique data source.

 

    References

Agee, E.M. and S.R. Gilbert, 1989: An Aircraft Investigation of Mesoscale Convection over Lake Michigan during the 10 January 1984 Cold Air Outbreak. J. Atmos. Sci., 46, 1877-1897.

Atkins, N.T., R.M. Wakimoto, and T.M. Weckwerth, 1995: Observations of the Sea-Breeze Front during CaPE. Part II: Dual-Doppler and Aircraft Analysis. Mon. Wea. Rev., 123, 944-969.

Atkins, N.T., R.M. Wakimoto, and C.L. Ziegler, 1998: Observations of the Finescale Structure of a Dryline during VORTEX 95. Mon. Wea. Rev., 126, 525-550. Blier, W. and R.M. Wakimoto, 1995: Observations of the early evolution of an explosive oceanic cyclone during ERICA IOP 5. Part I: Synoptic overview and mesoscale frontal structure. Mon. Wea. Rev., 123, 1288-1310.

Bond, N.A, and M.A. Shapiro, 1991: Research Aircraft Observations of the Mesoscale and Microscale Structure of a Cold Front over the Eastern Pacific Ocean. Mon. Wea. Rev., 119, 3080-3094.

Chien, F.C., C.F. Mass, and P.J. Neiman, 2001: An Observational and Numerical Study of an Intense Landfalling Cold Front along the Northwest Coast of the United States during COAST IOP 2. Mon. Wea. Rev., 129, 934-955.

Doyle, J.D., and N.A. Bond, 2001: Research Aircraft Observations and Numerical Simulations of a Warm Front Approaching Vancouver Island. Mon. Wea. Rev., 129, 978-998.

Fankhauser, J.C., G.M. Barnes, M.A. LeMone, 1992: Structure of a Midlatitude Squall Line Formed in Strong Unidirectional Shear. Monthly Weather Review: Mon. Wea. Rev., 120, 237-260.

Liu, C.H., R.M. Wakimoto, and F. Roux, 1997: Observations of mesoscale circulations within extratropical cyclones over the North Atlantic Ocean during ERICA. Mon. Wea. Rev., 125, 341-364.

McGinley, J.A., S.C. Albers, and P.A. Stamus, 1991: Validation of a composite convective index as defined by a real-time local analysis system. Weather and Forecasting, 6, 337-356.

Miller, L.J., M.A. LeMone, W. Blumen, R.L. Grossman, N. Gamage, and R.J. Zamora, 1996: The Low-Level Structure and Evolution of a Dry Arctic Front over the Central United States. Part I: Mesoscale Observations. Mon. Wea. Rev., 124, 1648-1675.

Neiman, Paul J., M.A. Shapiro, L.S. Fedor, 1993: The Life Cycle of an Extratropical Marine Cyclone. Part II: Mesoscale Structure and Diagnostics. Mon. Wea. Rev., 121, 2177-2199.

Neiman, P.J., F.M. Ralph, M.A. Shapiro, B.F. Smull, and D. Johnson, 1998: An Observational Study of Fronts and Frontal Mergers over the Continental United States. Mon. Wea. Rev., 126, 2521-2554.

Neiman, P.J. and R.M. Wakimoto, 1999: The Interaction of a Pacific Cold Front with Shallow Air Masses East of the Rocky Mountains. Mon. Wea. Rev., 127, 2102-2127.

Raga, G.B., R.E. Stewart, J.W. Strapp, 1994: Mesoscale Structure of Precipitation Bands in a North Atlantic Winter Storm. Mon. Wea. Rev., 122, 2039-2051.

Rasmussen, R.M., B.C. Bernstein, M. Murakami, G. Stossmeister, J. Reisner, and B. Stankov, 1995: The 1990 Valentine's Day Arctic Outbreak. Part I: Mesoscale and Microscale Structure and Evolution of a Colorado Front Range Shallow Upslope Cloud. J. App. Meteo., 34, 1481-1511.

Renfrew, I.A. and G.W.K. Moore, 1999: An Extreme Cold-Air Outbreak over the Labrador Sea: Roll Vortices and Air-Sea Interaction. Mon. Wea. Rev., 127, 2379-2394.

Shapiro, M.A., 1978: Further evidence of the mesoscale and turbulent sturcture of upper level jet stream-frontal zone systems. Mon. Wea. Rev., 106, 1100-1111.

Shapiro, M.A., and D. Keyser, 1990: Fronts, Jet Streams and the Tropopause; Chapter 10 from Extratropical Cyclones, AMS, 1990.

Wilson, J.W., G.B. Foote, N.A. Cook, J.C. Fankhauser, C.G. Wade, J.D. Tuttle, C.K. Mueller, and S.K. Krueger, 1992: The Role of Boundary-Layer Convergence Zones and Horizontal Rolls in the Initiation of Thunderstorms: A Case Study. Mon. Wea. Rev., 120, 1785-1815.

Weckwerth, T.M., J.W. Wilson, and R.M. Wakimoto, 1996: Thermodynamic Variability within the Convective Boundary Layer Due to Horizontal Convective Rolls. Mon. Wea. Rev., 124, 769-784.


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Prepared by Ed Szoke
Last modified: Fri August 31, 2001