Surface Layer Stability Transition Research Minimum 

Neutral Event-to-Sunrise Time Interval: 2001 September 

Case Study 

by Gail-Tirrell Vaucher and Manny Bustillos 

ARL-TR-2827 May 2003 

Approved for public release; distribution unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official 

Department of the Army position, unless so designated by other 

authorized documents. 

Citation of manufacturers’ or trade names does not constitute an 

official endorsement or approval of the use thereof. 
Army Research Laboratory 

White Sands Missile Range, NM 88002 

ARL-TR-2827 May 2003 

Surface Layer Stability Transition Research Minimum 

Neutral Event-to Sunrise Time Interval: 2001 September 

Case Study 

Gail-Tirrell Vaucher and Manny Bustillos 

Computation & Information Sciences Directorate, ARL 

Approved for public release; distribution unlimited. 

iii 

Contents 

Preface vi 

Acknowledgements vii 

Executive Summary 1 

1. Introduction 2 

 1.1 U.S. Army Interest In Atmospheric Stability Transition Research ....................................2 

 1.2 Civilian Interest In Atmospheric Stability Transition Research ........................................3 

 1.3 Purposes and Overview .......................................................................................................3 

 1.4 Background of the Stability Transition Study ....................................................................3 

 1.5 Character of the Stability Transition ..................................................................................6

 1.6 Ideal and Non-Ideal Stability Transition Forecast ..............................................................8 

2. Statistical Minimum In Seasonal Algorithm 9 

 2.1 2001 September Equinox-Atmospheric Surface Layer Test Overview ..............................9 

 2.2 Test Execution ................................................................................................................11 

 2.3 Test Results .......................................................................................................................12 

 2.3.1 General Weather Overview .....................................................................................12 

 2.3.2 Characterization of Nighttime, Transition, and Daytime Atmospheric Conditions 12 

 2.3.3 Observed Unique Features of the Three Stability Transitions ..............................13 

3. Discussion Of Results 13 

4. Summary and Conclusions 15 

Acronyms 16 

References 18 

Appendix A: Thompson Tower Data 21 

Appendix B: RAWINSONDE Data 43 
iv 

Report Documentation Page 59 

Figures 

Figure 1. Local Sunrise, SRNE Rule of Thumb, and NE Times, 1994 February-1995 June 

 (Raw Data) ......................................................................................................................5 

Figure 2. SRNE Rule of Thumb, Raw and Monthly Averaged NEs, 1994 February-1995 June ..5 

Figure 3. Monthly Averaged Sunrise Neutral Event Time Differences, 1994 April-1995 June ...6 

Figure 4. Coincident Cn2, Temperatures, and Insolation Time Series along a 1–km path for 24 

 March 2001 at HELSTF, NM .........................................................................................7 

Figure 5. Field Test Structures and Sensors Layout ....................................................................11 

Figure A1. Thompson Tower-2001 September 18: Temperature..................................................23 

Figure A2. Thompson Tower-2001 September 18: Relative Humidity ........................................23 

Figure A3. Thompson Tower-2001 September 18: Wind Speed ..................................................24 

Figure A4. Thompson Tower-2001 September 18: Wind Direction .............................................24 

Figure A5. Thompson Tower-2001 September 18: Pressure.........................................................25 

Figure A6. Thompson Tower-2001 September 18: Solar Radiation .............................................25 

Figure A7. Thompson Tower-2001 September 18: Delta-T..........................................................26 

Figure A8. Thompson Tower-2001 September 19: Temperature..................................................28 

Figure A9. Thompson Tower-2001 September 19: Relative Humidity ........................................28 

Figure A10. Thompson Tower-2001 September 19: Wind Speed ................................................29 

Figure A11. Thompson Tower-2001 September 19: Wind Direction ...........................................29 

Figure A12. Thompson Tower-2001 September 19: Pressure.......................................................30 

Figure A13. Thompson Tower-2001 September 19: Solar Radiation ...........................................30 

Figure A14. Thompson Tower-2001 September 19: Delta-T........................................................31 

Figure A15. Thompson Tower-2001 September 20: Temperature................................................33 

Figure A16. Thompson Tower-2001 September 20: Relative Humidity ......................................33 

Figure A17. Thompson Tower-2001 September 20: Wind Speed ................................................34 

Figure A18. Thompson Tower-2001 September 20: Wind Direction ...........................................34 

Figure A19. Thompson Tower-2001 September 20: Pressure.......................................................35 

Figure A20. Thompson Tower-2001 September 20: Solar Radiation ...........................................35 

Figure A21. Thompson Tower-2001 September 20: Delta-T........................................................36 
v 

Figure A22. Thompson Tower-2001 September 21: Temperature................................................38 

Figure A23. Thompson Tower-2001 September 21: Relative Humidity ......................................38 

Figure A24. Thompson Tower-2001 September 21: Wind Speed ................................................39 

Figure A25. Thompson Tower-2001 September 21: Wind Direction ...........................................39 

Figure A26. Thompson Tower-2001 September 21: Pressure.......................................................40 

Figure A27. Thompson Tower-2001 September 21: Solar Radiation ...........................................40 

Figure A28. Thompson Tower-2001 September 21: Delta-T........................................................41 

Figure B1. Thompson Tower RAOB Launch-2001 September 18: Temperature.........................45 

Figure B2. Thompson Tower RAOB Launch -2001 September 18: Relative Humidity...............45 

Figure B3. Thompson Tower RAOB Launch-2001 September 18: Pressure................................46 

Figure B4. Thompson Tower RAOB Launch-2001 September 18: ELR......................................46 

Figure B5. Thompson Tower RAOB Launch-2001 September 19: Temperature.........................48 

Figure B6. Thompson Tower RAOB Launch-2001 September 19: Relative Humidity................48 

Figure B7. Thompson Tower RAOB Launch-2001 September 19: Wind Speed..........................49 

Figure B8. Thompson Tower RAOB Launch-2001 September 19: Wind Direction ....................49 

Figure B9. Thompson Tower RAOB Launch-2001 September 19: Pressure................................50 

Figure B10. Thompson Tower RAOB Launch-2001 September 19: ELR....................................50 

Figure B11. Thompson Tower RAOB Launch-2001 September 20: Temperature.......................52 

Figure B12. Thompson Tower RAOB Launch-2001 September 20: Relative Humidity..............52 

Figure B13. Thompson Tower RAOB Launch-2001 September 20: Wind Speed........................53 

Figure B14. Thompson Tower RAOB Launch-2001 September 20: Wind Direction ..................53 

Figure B15. Thompson Tower RAOB Launch-2001 September 20: Pressure..............................54 

Figure B16. Thompson Tower RAOB Launch-2001 September 20: ELR....................................54 

Figure B17. Thompson Tower RAOB Launch-2001 September 21: Temperature.......................56 

Figure B18. Thompson Tower RAOB Launch-2001 September 21: Relative Humidity..............56 

Figure B19. Thompson Tower RAOB Launch-2001 September 21: Wind Speed........................57 

Figure B20. Thompson Tower RAOB Launch-2001 September 21: Wind Direction ..................57 

Figure B21. Thompson Tower RAOB Launch-2001 September 21: Pressure..............................58 

Figure B22. Thompson Tower RAOB Launch-2001 September 21: ELR....................................58 
vi 

Preface 

In 2001, the U.S. Army Research Laboratory, Meteorological-sensors Integration Team, 

conducted a series of three field tests in the southwestern desert of the United States. The 

purpose was to identify, characterize, and exploit repeatable atmospheric patterns found in the 

lowest layer of the Boundary Layer, the Surface Layer. The repeatable pattern selected was the 

Surface Layer Stability Transition. Each field test was timed with the purpose of validating a 

seasonal extreme in the annual morning Stability Transition (ST) timing cycle. The first 

seasonal minimum (Equinox month-March 2001) and the seasonal maximum (Solstice monthJune) were documented in separate Technical Reports. This Technical Report focuses on the 

second seasonal minimum occurring in the Equinox month of September. 

Each field test served as a building block in the overall goal of modeling the ST. The 

information gained from these field tests has three fundamental links to the U. S. Army and to 

the military in general: 

1. This research expands on U.S. Army Chief of Staff Shinseki’s vision. 

2. The knowledge of exploitable atmospheric characteristics, such as an ST, enhances electrooptical weapon effectiveness and efficiency. 

3. The accurate ST forecasts provide crucial initializing information for atmospheric models 

that forecast chemical and biological weapon effects, as well as transport and diffusion 

effects. 
vii 

Acknowledgements 

Appreciation is extended to the Meteorological-sensors Integration Team (MIT) members for 

their successful execution of the 2001 June Atmospheric Surface Layer Field Test. The MIT 

Team members included: Robert Brown, Edward Creegan, Doyle “Scott” Elliott, Alfred 

Gutierrez, David Quintis, Gail Vaucher (Team Leader) and Jimmy Yarbrough. Also, 

appreciation goes to Ms. Nancy Fudge, for her efforts in linking the remote site field test 

activities with the demands of the standard work hour routines.
1 

Executive Summary 

U.S. Army Chief of Staff Shinseki stated that his U.S. Army vision was to see first, act first, and 

kill first. In GovExec.com’s Daily Briefing, Freedberg Jr. wrote that the most powerful, accurate 

and quickest weapon on the planet is the laser. Both military concerns have one major hurdle, 

“seeing” through the atmosphere. The Surface Layer Stability Transition (SLST) Research has 

been investigating naturally occurring atmospheric patterns that enhance or detract from the 

successful “seeing” mission. These same Stability Transition (ST) patterns also provide 

knowledge of when the effects of chemical and biological weapons will shift from foe (toxic 

concentrations in a limited area) to friendly (non-toxic concentrations in a broad area), and vice 

versa. Likewise, initializing the convective Boundary Layer growth phase (ST) impacts civilian 

and military Atmospheric Dispersion/Diffusion Model accuracy. For the military, knowing when 

a smoke screen will “clear”, for example, could prove to be a significant strategic advantage on a 

battlefield. 

In 2001, the Meteorological-sensors Integration Team conducted three field tests with the 

primary purpose of characterizing, modeling, and exploiting repeatable patterns in the lower 

portion of the Atmospheric Boundary Layer. The repeatable patterns investigated were the 

morning ST, or Neutral Events (NE). The 2001 September 19–21 dates were selected based on a 

forecasted minimum time interval between the local Sunrise and an Ideal Case stability 

transition. Two other correlated field tests addressed the seasonal sunrise-to-NE time interval 

maximum and alternate minima (2001 June and March, respectively). These latter Tests were 

documented separately. 

The SLST research pursued two measurement and analysis methods: Eulerian (Tower data) and 

quasi-Lagrangian (Rawinsonde data). The September 2001 results yielded both Ideal and Nonideal ST condition cases. All observed NE served to validate the ST Forecast Model. Also 

gleaned from the data was a constructive characterization of the atmospheric conditions 

prompting the more difficult to understand Non-ideal Multiple and Extended NEs. In short, 

while reduced-insolation was empirically linked with the Multiple-NEs, the Extended-NEs were 

associated with increased ground and low-level moisture. The Test results documented here 

serve as a useful building block in support of their primary purpose. 
2 

1. Introduction 

This publication is the last of three technical reports documenting the 2001 Surface Layer ST 

Field Tests. Sections 1.1 and 1.2 are reproduced from the Surface Layer Stability Transition 

Research, Minimum Time Delay from Sunrise: 2001 March Case Study (Vaucher et al., 2003). 

1.1 U.S. Army Interest in Atmospheric Stability Transition Research 

Atmospheric Stability Transition (ST) Research links to military interests in at least three arenas. 

In the July 2002 Army Materiel Command Newsletter, U.S. Army Chief of Staff Shinseki stated 

that his vision for the U.S. Army was “to see first, act first, kill first...To see first, we must have 

persistent and pervasive intelligence-gathering capabilities” (Burlas, 2002). The atmosphere is 

one of the major hurdles retarding the efficiency of “seeing first.” The Boundary Layer 

Exploitation Task-Surface Layer Stability Transition (SLST) Research has been investigating 

naturally occurring atmospheric patterns that enhance or detract from the successful “seeing 

first” capability. Under favorable atmospheric conditions, target identification is potentially 

done quicker, making the last two actions of the Shinseki’s U.S. Army vision more efficient and 

effective. 

Sydney Freedberg Jr. wrote in his GovExec.com Daily Briefing, that the most powerful, most 

accurate and quickest weapon on the planet, the laser, has one major obstacle, the weather 

(Freedberg, 2001). To quantify the atmospheric impact on this, or any other electro-optical (EO) 

weapon, one needs to understand a parameter called “seeing”. To an astronomer, “seeing” is the 

arc second or angle occupied by the star image at the full-width and half-maximum of its 

intensity profile, as viewed from a specific point in the atmosphere (Businger et al., 2002). 

“Seeing” improves or degrades with changes in the atmospheric optical turbulence strength and 

location as quantified by profiles of the refractive index structure function Cn

2

. The SLST 

Research grew out of EO propagation research, and now serves as a building block for 

understanding and forecasting the naturally occurring atmospheric cycles that are both favorable 

and non-favorable for the laser and any subset of this weapon type. 

Finally, a significant urban warfare hazard is the release of chemical and biological weapons. 

The atmosphere, specifically the Boundary Layer convection, can enhance or detract from the 

weapon’s effectiveness. From a military perspective, knowledge of a ST means knowledge of 

when the chemical and biological weapon’s effect will shift from foe (toxic concentrations in a 

limited area) to friendly (non-toxic concentrations in a broad area), and vice versa (Angevine et 

al., 2001). 

Likewise, initializing the convective Boundary Layer growth phase (the ST) is a primary interest 

to civilian and military Convective Boundary Layer and Atmospheric Dispersion/Diffusion 
3 

Modelers. Model results often reflect the initial input accuracy. For the military, knowing when 

a smoke screen will “clear”, for example, could prove to be a significant strategic advantage on a 

battlefield. Thus, the ST pattern ties to both military and civilian applications (Angevine et al., 

2001). Additional civilian interests will be described in the next section. 

1.2 Civilian Interest in Atmospheric Stability Transition Research 

The Atmospheric Boundary Layer behavior during the period between the fully developed 

convection of mid-day and the stable conditions of the nocturnal Boundary Layer is poorly 

understood, but is of interest in several fields, including chemical and pollutant modeling 

(Grimsdell and Angevine, 2002). Grimsdell and Angevine focused their work on the afternoon 

ST in agricultural environments. However, their assessment regarding the poor understanding is 

also true for the morning Surface Layer ST in a desert environment. 

Finally, in the June 2002 Bulletin of the American Meteorological Society, Businger et al., 

describe the unique weather forecasting requirements for the highly technical stellar viewing at 

Hawaii’s Mauna Kea Observatories. Clear air turbulence in both the free atmosphere and in the 

Boundary Layer were flagged as causes for image distortion and blurring for their ground-based 

telescopes. Forecasting the observing quality for seeing parameters accurately is a key factor in 

the successful scheduling of these very expensive civilian optical and infrared instruments. 

Knowing when the atmospheric impact would be minimal, such as during a ST, would be a 

significant improvement and enhancement for the astronomical community (Businger et al., 

2002). 

1.3 Purpose and Overview 

This technical report is part of the U.S. Army Research Laboratory’s (ARL) Fiscal-Year (FY) 

2002 Boundary Layer Exploitation Task. The Task’s governing purpose was to characterize, 

model and exploit the lower portion of the Atmospheric Boundary Layer, the Surface Layer. 

The specific topic targeted for exploitation was the Surface Layer ST. The ARL Meteorologicalsensors Integration Team (MIT) conducted three ST field tests in FY 2001 (March, June and 

Sept 2001). Key results and new understandings gained from the last Test, the 2001 September 

Equinox-Atmospheric Surface Layer Field Test, are reported within this document. The Test 

was executed at White Sands Missile Range (WSMR), NM. One of the primary objectives for 

the field test was to validate the proposed Seasonal Algorithm used in the morning ST Forecast 

Model (Vaucher and Endlich, 1995). 

1.4 Background of the Stability Transition Study 

The following historical review of the ST study is reproduced from the Surface Layer Stability 

Transition Research, Minimum Time Delay from Sunrise: 2001 March Case Study (Vaucher et 

al., 2003). 
4 

The initial ST study was funded by the Atmospheric Science Laboratory and conducted at the 

U.S. Army-owned High Energy Laser Systems Test Facility (HELSTF), NM in the mid-1990s 

(USASL Contract). This study was prompted by an operational need to minimize the impact of 

atmospheric optical turbulence (AOT) on the High Energy Laser (HEL) when propagating along 

a 1 km path. Based on observations, the HELSTF meteorologists noted that twice a day the 

AOT would drop to a minimum. These AOT minima correlated closely with the morning and 

evening STs. 

Over time, ARL meteorological operational researchers developed a “rule of thumb” approach 

for forecasting the morning and evening STs. This “rule of thumb” suggested that a minimum 

amount of AOT occurred when the atmosphere was neither stable, nor unstable, and that such a 

“Neutral Event (NE)” occurred 60 min after sunrise, and 40 min before sunset. While the “rule 

of thumb” was able to yield a ballpark accuracy, the high cost of HEL testing quickly demanded 

a more precise forecast. Thus, a more rigorous investigation began. 

In 1994, Vaucher and Endlich published results from the first of two significant studies. 

According to their 2-month study, the average occurrence of the morning NE was about 70 min 

after sunrise. The time difference between sunrise and the associated NE ranged between 40 and 

133 min after sunrise. The evening NE occurred an average of about 60 min before sunset, with 

a Sunset-NE time difference ranging between 98 and 12 min before sunset (Vaucher and 

Endlich, 1994). They also noted that there was an implied trend in their statistical findings. 

Consequently, a follow-on study was pursued. 

In 1995, Vaucher and Endlich published the results from a 16-month AOT NE study conducted 

at HELSTF, NM. Recognizing the local heat flux as the primary contributor to AOT, the authors 

isolated three variables (Sunrise/Sunset time, Delta-T and Insolation) related to the heat flux, and 

observed their relationship to the NE over a 1 km desert path. The 16 m minus 2 m Temperature 

(T) difference (Delta-T) was examined at the start and end of the sampling path. Results 

reported near-surface, slightly dry adiabatic conditions present during a NE. The NE-insolation 

values showed that the ranges of insolation magnitudes at the Sunrise-NE were about twice those 

sampled at the Sunset-NE. This observation was explained as a function of the sun’s elevation. 

The most significant discovery of the 1995 study, with respect to ST forecasting, came while 

overlaying local sunrise and NE times. The minimum average time difference between local 

sunrise and NE was reported in the Equinox months. The maximum monthly time difference 

average occurred in the Solstice months. Vaucher and Endlich theorized that the skewed diurnal 

heating-cooling cycle of the solstice periods generated strong near-surface temperature 

inversions that delayed the transition into the near-dry adiabatic atmosphere required for a NE. 

During the Equinox, the 24-h heating-cooling cycle was nearly equal. Therefore, minimal time 

was needed for the day or nighttime atmosphere to transition into the near-dry adiabatic 

environment (Vaucher and Endlich, 1995). 
5 

Figure 1 displays the seasonal effect discovered by Vaucher and Endlich. In this figure, the 

Sunrise NE (SRNE) Rule of Thumb Forecast is contrasted with the actually observed NE time. 

Figure 1. Local Sunrise, SRNE Rule of Thumb, and NE Times, 1994 February-1995 

June (Raw Data). 

To display the oscillation more plainly, figure 2 shows the “rule of thumb”, the monthly 

averaged NE time, and the actual NEs. 

Figure 2. SRNE Rule of Thumb, Raw and Monthly Averaged NEs, 1994 February-1995 June. 
6 

Removing the actual data, figure 3 shows the annual cycle of average NE by month. Note he 

Equinox NE minima (September, March) and the Solstice NE maxima (June, December). The 

first minimum is ignored due to the lack of data for the initial month. 

Figure 3. Monthly Averaged Sunrise Neutral Event Time Differences, 1994 April-1995 June. 

Based on the 16-month study, Vaucher and Endlich updated the Rule of Thumb NE Forecast 

approach by introducing a seasonal correction curve. The coefficients produced by the Fourier 

Waveform Analysis can be found in their 1995 Battlefield Atmospheric Conference paper 

(Vaucher and Endlich, 1995). 

The 16-month study left some unanswered questions: 

1. Are the updated Rule of Thumb NE Forecast algorithms site specific? What about a nondesert environment? What about other latitudes? 

2. Is the seasonal oscillation real or a coincidence? 

3. The current model works under Ideal atmospheric conditions. What about under Non-ideal 

conditions (see section 1.6)? 

ARL addressed some of these questions during the FY01 field tests. First, however, this report 

examines the ST character and the Ideal versus Non-ideal atmospheric conditions.

1.5 Character of the Stability Transition 

The ST character is best understood by examining a full 24-h stability cycle. Figure 4 presents a 

“typical” diurnal (a March Equinox AOT time series over a high elevation desert site in the 

southwestern United States) and can be used as a visualization tool for the following stability 

cycle description. Additional information on typical stability cycles can be found in 

Meteorology for Scientists and Engineers (Stull, 2000) and An Introduction to Boundary Layer 

Meteorology (Stull, 2001). 
7 

1E- 19

1E- 18

1E- 17

1E- 16

1E- 15

1E- 14

1E- 13

1E- 12

1E- 11

1E- 10

0 3 6 9 12 15 18 2 1 2 4

Local Time (Dec Hr - MST)

Cn

2 (m-2/3)

Cn2 : 1km, 8 m AGL

S unrise ( 6 .0 7 MS T)

S unse t ( 18 .3 3 MS T)

 

0

5

10

15

20

25

0 3 6 9 12 15 18 21 24

Local Time (Dec Hr - MST)

Temperature (C)

Tem perat ure (2 m)

Tem perat ure (1 6m )

Sunrise (6.07 MST)

Sunset (1 8.33 MST)

0

200

400

600

800

1000

1200

0 3 6 9 12 15 18 21 24

Local Time (Dec Hr - MST)

Insolation (W/m2

)

Insolation

Sunrise (6.07 MS T)

Sunset (18.33 MST)

Figure 4. Coincident Cn

2

, Temperatures, and Insolation Time Series 

along a 1 km path for 24 March 2001 at HELSTF, NM. 

0000-Sunrise. Under clear skies, calm winds, and low ground moisture, the desert basin at 0000 

hours Local Time is stably stratified. The coldest temperatures are at the lowest levels (Delta-T 

> 0). The heat flux is negative, and the AOT is a moderate-to-low level. Katabatic flow off 

neighboring mountains serves as a catalyst for overturning and mixing the nighttime stable 

atmospheric layers. The result is a mélange of density variations, which produces intermittent 

maxima of AOT. If winds decrease, AOT will return to the normal moderate-to-low level. 

Sunrise occurs. The rays of sunrise start warming the ground, which radiates heat into the lowest 

atmospheric layer. The heat flux steadily increases, causing the stable atmosphere to become 

isothermal and “neutral.” Cn

2

, coincidently, drops to a minimum. This is the morning, or 

Sunrise AOT NE. 
8 

Daytime. As the sun continues warming the ground throughout the morning, the neutral stability 

shifts into an unstable state. The heat flux is positive. The vertical temperature differences are 

now negative and Cn

2

 increases. Atmospheric convection attempts to rebalance the unstable 

conditions by mixing the near surface warm air into the cooler air aloft. The persistent sun 

strengthens the unstable state, deepening the mixed layer. The constant mixing intensifies the 

atmospheric density variations and the AOT further increases. AOT reaches a peak around 

midday, or soon after. 

The waning of the sun in the clear afternoon skies reduces the insolation and decreases the 

negative Delta-T magnitudes. Subsequently, AOT decreases. Just prior to sunset, the 

atmosphere briefly becomes near-dry adiabatic (neutral) and Cn

2 drops to a minimum. The heat 

flux goes to zero and the day’s second NE takes place. 

Sunset occurs. Civil, Military and Astronomical Twilights quickly evolve until there is the 

nighttime darkness. The previously warmed soil strongly emits the Solar Radiation absorbed 

during the daylight hours and cools rapidly. Delta-T becomes positive, confirming the presence 

of a stable atmosphere. Colder, heavier air, from the surrounding mountains and hills, drains 

into the valleys, serving as a mixing tool. The non-uniform radiative cooling and clear sky 

drainage flow creates an ambient mixing, which keeps the AOT at a moderate level throughout 

the night. The moderate AOT is punctuated by occasional, intermittent AOT maxima. 

Within the diurnal cycle just described, the two primary NE times are clearly linked with the 

local sunrise and sunset. As the stable nighttime conditions transition to unstable daytime 

conditions, a Sunrise NE occurs. Likewise, as the unstable daytime evolves to a stable nighttime 

atmosphere, a Sunset NE occurs. Common to both scenarios is a period in which the atmosphere 

is near-dry adiabatic, exhibiting the least variations of Cn

2 along a horizontal and vertical path. 

The target of the SLST research is to successfully forecast the initial time for these transition 

events (Vaucher et al., 2003). 

1.6 Ideal and Non-ideal Stability Transition Forecast Standards 

Two distinct scenarios, Ideal and Non-ideal atmospheric conditions, were observed during the 

mid-1990 ST studies: 

1. Ideal atmospheric conditions were defined as clear skies, low winds and low ground 

moisture. 

2. Non-ideal atmospheric conditions included all other atmospheric traits, especially any 

cloud occultation of the sun during sunrise/sunset. 

Local atmospheric conditions determined the ST duration. Under Ideal conditions, the transition 

was often less than 2 min. Ironically, the Ideal condition ST forecast (with seasonal correction 

algorithms) produced the best results for the HELSTF, WSMR, NM site. In fact, one could 

accurately forecast to the minute when a Sunrise NE would occur 9 months in advance of the 

forecast, presuming that the day of validation had Ideal atmospheric conditions. 
9 

Forecasting for the Non-ideal atmospheric scenario was another story. First, the NE duration 

was anywhere from 1 min to over 20 min In the 2001 June Solstice-Atmospheric Surface Layer 

Test, a nighttime NE existed for over 20 min. Another characteristic of Non-ideal scenarios was 

the generation of multiple NEs. Some major contributors to these Non-ideal NE conditions 

included: 

1. Solar disc occultation during sunrise/sunset. 

2. Sun ray obscuration after sunrise/before sunset. 

3. The presence of local ground moisture. 

4. The presence of non-standard local forcing (such as a frontal passage). 

2. Statistical Minimum In Seasonal Algorithm 

2.1 2001 September Equinox-Atmospheric Surface Layer Test Overview 

The 2001 September Equinox-Atmospheric Surface Layer Test was executed in three phases: 

two Pre-Tests (5–7 and 18 September), and the actual Test (19–21 September). The test site 

used was the 100 ft Thompson Tower site (Lat: 32.35, Long: –106.47), in WSMR, NM, with a 

scintillometer path extending about 1 km west-southwest to Ammo Site. The participants of the 

Test included MIT and David Tofsted of ARL’s Weather Exploitation Branch, who provided 

support for the Cn

2

 equipment. The Test Coordinator/Director was Gail Vaucher. Acting Test 

Director for 28 August to 14 September was Scott Elliott. The Test Schedule was designed 

around mission and travel requirements. The four objectives of the Test, with their point-ofcontacts (POC), were: 

1. To be the third of three FY 2001 sampling sets aimed at verifying the maximum and 

minimum magnitudes of the Neutral Event Forecasting Model seasonal effects (POC: Gail 

Vaucher). 

2. To quantitatively characterize the desert atmospheric Surface Layer by studying the 

atmospheric thermodynamics and Surface Layer advection during the night-to-day 

transition period (POC: Doyle “Scott” Elliott). 

3. To characterize atmospheric transition events aloft, via the Wind Profiling Radar (POC: 

Edward Creegan). 

4. To obtain high data rate Cn

2

 measurements over a 950 m path (POC: David Tofsted). 
10

Prior to the field test execution, the Thompson Tower site 4 m scintillometer scaffolding tower was

moved to the Ammo Site. A single, 5 m meteorological tower replaced this scaffolding at Thompson

Tower. Elevated cabling posts were used at Ammo Site and Thompson Tower to prevent future

damage to the cables caused by local wildlife (which had damaged previous cabling). The temporary

housing for the computer equipment at the remote Ammo Site was provided by a Commercial Utility

Cargo Vehicle with shelter. The power for the site was a mobile 20 kW generator. A mobile High

Speed Trailer (HST) attached to hard power provided the equivalent at the Thompson Tower site. The

versatile HST served as a Post-test data processing center and Testers’ Conference Room.

Meteorological sensors included a 4 m TacMet II Unit, and a 10 m 3-level tower of 3D Sonic Anemometers at the Ammo Site. A Campbell Data Logger linked two Thompson Tower surface sensor

units (2 m and ~ 38 m levels). Vaisala global positioning system (GPS) rawinsondes were launched

from a High Mobility Multi-Wheeled Vehicle (HMMWV) situated west of Thompson Tower. The

HMMWV also served as the housing for the 924 MHz Wind Profiling Radar. The Radar Antenna was

placed west of Thompson Tower and slightly southwest of the HMMWV. A 25 kW Quiet Generator

powered the HMMWV. The HST was placed north and slightly west of Thompson Tower, and used

hard power. Figure 5 shows the Field Test Structures and Sensors Layout.
11

 Figure 5. Field Test Structures and Sensors Layout.

A Pre-Test equipment and acquisition capability check was conducted 5–7 and 18 September 2001.

Thompson Tower meteorological sensors, Radar, and RAOB systems successfully ran simultaneously.

The Sonic and Scintillometer equipment were installed and aligned prior to the Test. These latter

systems were under development, therefore, each unit was employed as the system became functional.

Thompson Tower and the Ammo Site tower data were deemed acceptable during the Pre-Tests.

2.2 Test Execution

Test Days 1–3 (2001 Sep 19–21) began at 0400 Mountain Daylight Time (MDT), with all participants

traveling to the 100 Ft Thompson Tower in a caravan. This strategy served to minimize desert dust

around the field site. There were three data acquisition cases scheduled per day. These cases characterized the nighttime desert atmosphere (0500–0700 MDT), the onsite ST/NE (0700–0900 MDT), and

the daytime desert atmosphere (0900–1100 MDT). Due to an imposed administrative restriction on

work hours, this latter case had to be shortened. After each test day, all data were plotted, reviewed

and discussed by the six onsite participants (Vaucher, 2001).

100 Ft Thompson Tower - WSMR, NM, Desert Lapse Rate Test (Sep 18-21, 01)

E

S

W

AG

High Speed

Trailer

43’ 10”

N

P

o

l

e

HMMWV

Latitude(decimal deg):32.36 N [+32.36]

Longitude(decimal deg): 106.42 W [-106.42]

Elevation (meters MSL): 1213

Date of Survey: 09/21/01

Surveyed by: Alfred Gutierrez/Dave Quintis

Thompson Metal Tower

Longitude –106 degrees 25 min 11 sec (W) 

Latitude 32 degrees 21 min 50 sec (N)

Ammo Site Metal Tower

Longitude -1060 25.733 Min (W)

Latitude 320 21.629 Min (N)

143’ 11”

T

a

r

g

e

t

P

o

l

e 145’ 4”

56’ 2”

3116.8’ 

TACMET II

12’ ground

to sensor

Temp & RH

2m approx

18’ 9” approx

Generator

Radar

45’ 10”

Pig

108’ 2”

(mdl 5103)

o o o o

o o

13’ 7” scintillometers 13’ 7” scintillometers

Temp RH @ 38m

WS/WD @ 39m

Barometer @ 105’

Solar Sensor @ 36m

Helium Tanks

61’ 9”

34’ 5”

o

Gen44’ 10”

5’ 2”

10 meter

Sonic Tower

231’ 10”

3D Sonic Tower

Longitude -106 degrees 25.741’ (W)

Latitude 32 degrees 21.663‘ (N)

5 meter tower

Scintillometer

13’

Not to Scale
12

A morning WSMR mission coincided with Test Day 3. Working cooperatively with the WSMR Met

Team, ALL RAOB launches were released on schedule at the Thompson Tower site. The Thompson

Tower data for all cases ran uninterrupted. A Team member, working normal business hours on the

WSMR Post provided daily synoptic weather charts and administrative information. Cell phones and

radios helped maintain communications and safety between sites.

2.3 Test Results

This section begins with a General Weather Overview, followed by a brief characterization of the

Nighttime (Stable), Transition (NE), and Daytime (Unstable) Sub-cases. Finally, unique features

of the three observed NEs are described.

2.3.1 General Weather Overview

Throughout the three-day Experiment, an upper-level High was centered over Northern Mexico.

The WSMR rawinsondes reported that the site was under the High’s westerly flow. Weak disturbances drifted around the upper High, bringing some moisture with them. Local skies ranged

from mostly sunny to partly cloudy. Though there was not enough moisture for a monsoon

thunderstorm build-up, some morning ground moisture was observed (Forecast for White Sands

Missile Range, Intellicast.com, Real-Time Weather Data, 2001).

2.3.2 Characterization of Nighttime, Transition, and Daytime Atmospheric Conditions

Atmospheric conditions for Day 1 were near Ideal: clear skies, low winds, and some ground moisture.

Day 2 was characterized as Non-ideal: morning clouds obscured the sunrise causing multiple and

extended STs. Day 3 was both Ideal and Non-ideal: the immediate eastern horizon was initially clear of

clouds, but soon after the solar disc rose, clouds filtered the warming rays. Winds were light, and

ground moisture was observed (dew on the Radar Radome).

Nighttime (0500–0700 MDT). Pressure (P) increased slightly (less than +1.5 mb). Characteristically

cool temperatures were sampled near the surface, generating a Delta-T range of +2 to +7 oC. Relative

Humidity (RH) was 20–50 percent, with 2 m RH greater than the 38 m RH. Winds were less than 5 m/

s, with generally divergent magnitudes between the 5 and 39 m sampling heights. Wind directions (WD)

were also divergent, with the lowest surface winds primarily from the northern quadrants.

Transition (0700–0900 MDT). The P continued to increase with time (+1 to +1.4 mb). Delta-T began

with a Stable +4 oC (2 m < 38 m). After the transition (NE), Delta-T was approximately 2 oC (Unstable). The greatest Delta-T change generally occurred minutes before the first ST (between 0741–

0750 MDT). The RH began with an upper verses lower RH differential of 20–40% (greatest RH at 2

m). Then, like Temperature (T), the independent RH sensors reported a transition in the humidity. The

post-transition RH difference was less than 5%, with the dryer conditions generally at 2 m. Wind

speeds (WS) between the 5 and 39 m levels were less than 5.5 m/s. While the upper and lower levels

began as pseudo-independent airflow, the magnitudes appeared to converge at the time of transition.

This convergence was noted in the 2001 June Case Study. The unified condition persisted throughout
13

the end of this case. Intermittent cloud cover was quantified by independently observed “Percentage of

Sun” disc occultation, as seen through a Welder’s Glass.

Daytime (0900–1100 MDT). The smallest P increases occurred during this time period (+0.4 to +0.5

mb). The Delta-T consistently hovered between –1.2 and –1.9 oC, with the warmest T at 2 m (Unstable). The RH differences (2 and 38 m) were less than 5%. The WS was < 4.5 m/s, with both tower

levels reporting a relatively unified direction. Cloud obscuration was generally less over this time period.

2.3.3 Observed Unique Features of the Three Stability Transitions

All three STs occurred within the forecasted times. That is, the forecasted time plus or minus the

standard deviation for September.

Day 1(19 September). The clear morning skies yielded a single, 4-min, uninterrupted ST. Ground

moisture, in the form of dew, was observed on the radar’s antenna.

Day 2(20 September). The Non-ideal conditions (beginning with clouds obscuring the sunrise)

created multiple and extended STs. Despite the occulted sunrise, the first of these transitions

occurred at the forecasted time. Based on Delta-T magnitudes, the second transition extended for

about 18 min. Graphically, this event might be interpreted as two events. The final transition

occurred shortly after, and consumed the least amount of time. Dew was evident during this test

day.

Day 3(21 September). Day 3 presented both Ideal and Non-ideal conditions. Clear skies were

observed before and after the sunrise. During sunrise, there were non-occulting clouds reported

along the eastern horizon, and local ground moisture (Non-ideal) noted. A brief solar disc cloud

obscuration was observed just prior to the ST. It is interesting to note that the single observed NE

occurred prior to the forecasted time, but within the forecasted standard deviation for September.

3. Discussion Of Results

For this discussion, the analysis is narrowed to each Day’s actual NE. Placing the NE in the

center and allowing a buffer of 30 min before and after the center point, we now re-examine the

attributes of the atmosphere surrounding the morning transition(s) and contrast them with the

previous 2001 Field Experiments.

Multiple and extended STs were reported in the 2001 June Case Study Technical Report (Vaucher and

Bustillos, 2003). This September study also documents multiple and extended transitions. Unlike the

June Study, however, all NEs occurred after sunrise and were initiated within the standard deviation of

the forecasted NE. Unlike June, local forcing came in a much more subtle manner, namely no fronts or

local thunderstorms were observed in the Test area. Instead, the primary suspects for generating these

multiple and extended events included the expected solar disc obscuration by clouds, as well as the

ground moisture observed as local dew. With this in mind, we again review each Day’s NE.
14

Day 1 displayed an extended (4 min) NE. Winds at the 2 m and 39 m levels were all less than 2 m/s,

confirming a lack of local dynamic forcing. The highest 2 m RH was measured soon after local sunrise

(approximately 96%). The coincident and significantly dryer 38 m RH implied an independent air mass

aloft. As the NE approached, the 2 m RH dropped to about 70%. The 38 m RH dried less than 10

percent. Within 10 minutes after the transition, the lower and upper air masses completed their initial

homogenizing mixing, with the 2 m RH showing a slightly dryer value than the 38 m RH. Due to the lack

of cloud cover, the only explanation for the slightly extended transition would be that the ground moisture “damped” the rate of change in the surface heat flux. The fact that the surface RH remained slightly

dryer than above indicates that the ground moisture’s impact on the atmosphere was quickly overcome

by the full solar heating under clear skies.

Day 3 reported the more typical NE (2 min). On this day, the highest 2 m RH occurred just after

sunrise (around 75%). The 38 m RH paralleled Day 1, in that it showed a much dryer air mass

aloft. However, unlike Day 1, there is no same-direction drying trend between these two layers.

Instead, while the lower layer slowly dries, the upper air mass gains moisture. This upward

moisture flux continues until the two layers report their first mutual RH value (~ 65%), which

also coincides with the morning NE.

Why did the NE occur on the late side of the forecasted value for Day 1 and the early side for

Day 3? One possible answer rests in the moisture factor. Ground moisture was observed on both

days. Distinguishing the two cases is that the 38 m level acted as a sponge on Day 3. Perhaps

the liberal upward mixing of moisture allowed the local environment to transition early. Whereas

on Day 1, the moisture was not so easily upward-mixed, and thereby served as a retarding agent

in the process of transitioning.

Day 2 presents multiple (three) STs. The durations of the STs, in chronological order, were 6, 18

and 2 minutes. These times were determined from the empirical Delta-T bounds defined in the

2001 June Case Study, namely +/–0.25 oC. At sunrise, the 2 m and 38 m levels appeared to be

independent air masses: winds aloft were about 2–3 m/s faster than at the surface, 2 m RH was

around 65%, and 38 m RH was around 45%. At the first NE, which coincided with the forecasted NE, the 2 m RH had only dried to 58%. By the end of the last ST, the 2 m RH was 55%.

Little variation was reported between these points. Though one would expect mixing to bring the

upper and lower RH values together, the lower layer rose only about 5%. Even during the final

NE, the RH values are separated by about 3%, with the 2 m RH being the moister. Winds at both

levels were 3 m/s and less. The WD aloft was southeasterly and northeasterly at the surface.

Occulting cloud cover persisted throughout the 3 transitions.

Kunkel and Walters stated that refractive index fluctuations (Cn

2) were caused primarily by fluctuations

in temperature, and to a lesser extent by fluctuations in water vapor pressure (1983). After reviewing

the data from these three Field Experiments, we need to add our empirical understanding to their model

observations. That is, while multiple and extended STs are a function of reduced insolation (clouds
15

occulting the sun) and ground moisture, the multiple STs appear to correlate more strongly with reduced

insolation. Extended NEs appear to be associated with abundant local ground moisture.

4. Summary and Conclusions

The defining objective for the three FY01 field tests was to verify and validate the seasonal impact on

the near-surface STs (NEs). With limited personnel or hardware resources, we were only able to

address the maximum and minimum points on the seasonal curve discovered by Vaucher and Endlich

(1995). In the 2001 March Equinox-Atmospheric Surface Layer (ASL) Test, we were encouraged

when ideal atmospheric conditions yielded strong agreement with the forecasted event (Vaucher et al.,

2003). The 2001 June Solstice-ASL Test educated us in the effects of Non-ideal conditions. Data that

quantified (versus qualified) the multiple and extended STs was acquired and analyzed (Vaucher and

Bustillos, 2003). Finally, in the 2001 September Equinox-ASL Test, we observed both Ideal and Nonideal atmospheric conditions. The true character of these two scenarios was examined, and two repeatable Non-ideal condition attributes were added to our understanding. Does this conclusively mean that

the seasonal algorithm is verified? Yes and no. Under Ideal conditions, the model was successful.

Under Non-ideal conditions, the model was not successful in the 2001 June Case Study, but was

successful in the 2001 September Case Study. If we extend this to the other questions posed in Section

1.4, we have evidence that the seasonal algorithm is not unique to just the original desert data site. We

also have quantitative proof that (1) these STs can occur multiple times during the day AND night, (2)

transition conditions can continue for at least 26 min, (3) ground moisture is a significant factor in

generating Extended STs and (4) reduced insolation (solar disc occultation by clouds) tends to yield

Multiple STs. Finally, these three field tests have produced 9 case studies that quantitatively characterize the desert-atmospheric Surface Layer’s night, transition and daytime conditions.

What’s next? The Boundary Layer Exploitation Task objective prompting these field tests was “to

identify, characterize, model and exploit repeatable patterns within the Atmospheric Surface Layer that

are useful to the military” (Vaucher, 2001). These tests have indeed identified the repeatable atmospheric Surface Layer ST pattern. The data has quantitatively added to the characterization of the

transition pattern, as well as validated the Ideal Scenario parts of the ST Forecast Model. As we look

toward the model-improvement phase of the objective, we also need to re-examine the exploitable

attributes of this atmospheric research. U.S. Army Secretary Chief of Staff Shinseki’s 2002 vision was

“to see first”. With this research, we have expanded his vision to, “to see better.” Linking this work

with military EO propagation missions, such as reconnaissance/surveillance, IR sensors/weapons

effectiveness and HEL laser weapon systems, is just one area of exploitation. Other uses for a ST

Forecast Model would be as an information module in the larger military simulation and strategy models.

Finally, ST Forecast Models also have their niche as critical input modules (initializing point(s)) for

atmospheric chemical and biological weapon distribution/dispersion models that are based on the

atmospheric convective processes.
16

Acronyms

AOT Atmospheric Optical Turbulence

AGL Above Ground Level

ARL Army Research Laboratory

Cn

2 Index of Refraction Structure Function

Delta-T Temperature Difference [T38m – T2m]

ELR Environmental Lapse Rate

EO Electro-Optical

FY Fiscal Year

GPS Global Positioning System

HEL High Energy Laser

HELSTF High Energy Laser Systems Test Facility

HMMWV High Mobility Multi-wheeled Vehicle

HST High Speed Trailer

IR Infrared

MIT Meteorological-sensors Integration Team

MDT Mountain Daylight Time

MM5 Pennsylvania State University/National Center for Atmospheric Research

Mesoscale Model version 5

NE Neutral Event

P Pressure

POC Point of Contact

RAOB Rawinsonde Observation System

RH Relative Humidity

SLST Surface Layer Stability Transition

SR Solar Radiation
17

SRNE Sunrise Neutral Event

ST Stability Transition

T Temperature

WS Wind Speed

WSMR White Sands Missile Range

WD Wind Direction
18

References

Angevine, Wayne M.; Baltink, H.K.; Bosveld, Fred. Observations of the Morning Transition of the

Convective Boundary Layer. Boundary Layer Meteorology, 2001 (April 6).

Burlas, Joe. Army Prophet Debuts on Capitol Hill. The Command Post Newsletter; Army Materiel

Command, Army News Service: July 2002.

Businger, S.; McLaren, R.; Ogasawara, R.; Simons, D.; Wainscoat, R. Starcasting. BAMS 2002, 83

(6), 858–871.

Freedberg, Sydney J. Jr. Flash! Zap! Boom! Lasers come of age. National Journal, April 23, 2001.

Grimsdell, A.W.; Angevine, W.M. Observations of the Afternoon Transition of the Convective

Boundary Layer. Journal of Applied Meteorology, 2002 (January), 3–11.

Kunkel, K.; Walters, D. Modeling the Diurnal Dependence of the Optical Refractive Index Structure

Parameter. Journal of Geophysical Research, 1983, 88 (C15), 10999–11004.

Stull, Roland; An Introduction to Boundary Layer Meteorology; Kluwer Academic Publishers:

Norwell, MA, 1988.

Stull, Roland; Meteorology for Scientists and Engineers; 2nd Ed; Brooks/Cole Thompson Learning:

Pacific Grove, CA. 2000; Chapters 1-6.

U.S. Army Atmospheric Sciences Laboratory; Contract No: DAAD07-89-C-0035; Task No:

9015 a nd 9101.

Vaucher, Gail-Tirrell. 2001 September Equinox-Atmospheric Surface Layer Test, Test Summary,

White Sands Missile Range, NM. Internal ARL Document, 2001.

Vaucher, Gail-Tirrell; Bustillos, M. Surface Layer Stability Transition Research, Maximum Time D

Delay from Sunrise/Non-Ideal Conditions: 2001 June Case Study; Technical Report No:

ARL-TR-2823, to be submitted for publication, 2003.

Vaucher, Gail-Tirrell; Bustillos, M.; Gutierrez, A. Surface Layer Stability Transition Research,

Minimum Time Delay from Sunrise: 2001 March Case Study; Technical Report No: ARLTR-2798, to be submitted for publication, 2003.

Vaucher, Gail-Tirrell; Endlich, Robert. Forecasting Atmospheric Optical Turbulence Neutral EventsPart II. Proceedings of the 1995 Battlefield Atmospheric Conference, Army Research Lab,

White Sands Missile Range, NM, Dec 5–7, 1995.
19

Vaucher, Gail-Tirrell; Endlich, Robert. Forecasting/Modeling the Atmospheric Optical Turbulence

Neutral Events over a Desert Environment, Proceedings of the 1994 Battlefield Atmospheric

Conference, Army Research Lab, White Sands Missile Range, NM, Nov 29-Dec 1, 1994.

Forecast for White Sands Missile Range. http://weather.wsmr.army.mil/public/fcst.txt (accessed

September 2001) White Sands Meteorology Branch, WSMR Weather Support Center.

Intellicast.com. http://www.intellicast.com (accessed September 2001).

Real-Time Weather Data. http://www.rap.ucar.edu/weather (accessed September 2001) University

Corp for Atmospheric Research.
20
21

namic time-series data was acquired at the 2 m and 38 m above ground levels (AGL). Wind data were

acquired at 5 m and 39 m AGL. For convenience, we have designated data representing the lower

layer with a brown box and the upper layer with a blue open circle. Efficiency has dictated that all three

Sub-cases (Stable, Neutral, Unstable) be presented in a single time-series plot. Approximate times for

each Sub-case were:

Stable 0500–0600 MDT

Neutral 0700–0900 MDT

Unstable 0900–1100 MDT

The 2001 September 18 Pre-Test data were included for completeness. The following are the four

sections of Appendix A:

• Figures A1–A7: 2001 September 18

• Figures A8–A14: 2001 September 19

• Figures A15–A21: 2001 September 20

• Figures A22–A28: 2001 September 21

Appendix A: Thompson Tower Data

This appendix is part of ARL-TR-2827, Surface Layer Stability Transition Research Minimum Neutral

Event-to-Sunrise Time Interval: 2001 September Case Study, U.S. Army Research Laboratory, White

Sands Missile Range, NM 88002-5501.

A Eulerian (fixed point) perspective on the atmospheric conditions during the Nighttime (Stable) to

Daytime (Unstable) transition was quantitatively recorded by the Thompson Tower data. Thermody-
22

Figures A1–A7: 2001 September 18-Thompson Tower Data
23

0

10

20

30

40

50

60

70

80

90

100

15.0 15.5 16.0 16.5 17.0

Local Time (dec hrs)

Relative Humidity (%)

RH [2m]

RH [38m]

30

31

32

33

34

35

15.0 15.5 16.0 16.5 17.0

Local Time (dec hrs)

Temperature (C) 

Temp [2m]

Temp [38m]

Figure A2. Thompson Tower-2001 September 18: Relative Humidity.

Figure A1. Thompson Tower-2001 September 18: Temperature.
24

0

90

180

270

360

15.0 15.5 16.0 16.5 17.0

Local Time (dec hrs)

Wind Direction (deg) 

WD [5m]

WD [39m]

0

1

2

3

4

5

6

7

15 16 16 17 17

Local Time (dec hrs)

Wind Speed (m/s)

WS [5m]

WS [39m]

Figure A3. Thompson Tower-2001 September 18: Wind Speed.

Figure A4. Thompson Tower-2001 September 18: Wind Direction.
25

0

100

200

300

400

500

600

700

800

15.0 15.5 16.0 16.5 17.0

Local Time (dec hrs)

Solar Radiation (W/m^2)

872.6

873.6

874.6

875.6

876.6

15.0 15.5 16.0 16.5 17.0

Local Time (dec hrs)

Pressure (mb)

P [33m]

Figure A6. Thompson Tower-2001 September 18: Solar Radiation.

Figure A5. Thompson Tower-2001 September 18: Pressure.
26

-8

-6

-4

-2

0

2

4

6

8

15.0 15.5 16.0 16.5 17.0

Local Time (dec hrs)

Delta-Temperature ( C )

Delta-T [38m-2m]

Zero Line

Figure A7. Thompson Tower-2001 September 18: Delta-T.
27

Figures A8–A14: 2001 September 19-Thompson Tower Data
28

0

10

20

30

40

50

60

70

80

90

100

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Relative Humidity (%)

RH [2m]

RH [38m]

11

16

21

26

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Temperature (C) 

Temp [2m]

Temp [38m]

Figure A9. Thompson Tower-2001 September 19: Relative Humidity.

Figure A8. Thompson Tower-2001 September 19: Temperature.
29

0

90

180

270

360

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Wind Direction (deg) 

WD [5m]

WD [39m]

0

1

2

3

4

5

6

7

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Wind Speed (m/s)

WS [5m]

WS [39m]

Figure A10. Thompson Tower-2001 September 19: Wind Speed.

 Figures A11: Thompson Tower-2001 September 19-Wind Direction.
30

0

100

200

300

400

500

600

700

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Solar Radiation (W/m^2)

874

875

876

877

878

879

880

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Pressure (mb)

P [33m]

Figure A13. Thompson Tower-2001 September 19: Solar Radiation.

Figure A12. Thompson Tower-2001 September 19: Pressure.
31

-8

-6

-4

-2

0

2

4

6

8

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Delta-Temperature ( C )

Delta-T[38m-2m]

Zero Line

Figure A14. Thompson Tower-2001 September 19: Delta-T.
32

Figures A15–A21: 2001 September 20-Thompson Tower Data
33

0

10

20

30

40

50

60

70

80

90

100

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Relative Humidity (%)

RH [2m]

RH [38m]

15

20

25

30

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Temperature (C) 

Temp [2m]

Temp [38m]

Figure A16. Thompson Tower-2001 September 20: Relative Humidity.

Figure A15. Thompson Tower-2001 September 20: Temperature.
34

0

90

180

270

360

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Wind Direction (deg) 

WD [5m]

WD [39m]

0

1

2

3

4

5

6

7

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Wind Speed (m/s)

WS [5m]

WS [39m]

Figure A17. Thompson Tower-2001 September 20: Wind Speed.

Figure A18. Thompson Tower-2001 September 20: Wind Direction.
35

0

100

200

300

400

500

600

700

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Solar Radiation (W/m^2)

876

877

878

879

880

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Pressure (mb)

P [33m]

Figure A20. Thompson Tower-2001 September 20: Solar Radiation.

Figure A19. Thompson Tower-2001 September 20: Pressure.
36

-8

-6

-4

-2

0

2

4

6

8

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Delta-Temperature ( C )

Delta-T [38m-2m]

Zero Line

Figure A21. Thompson Tower-2001 September 20: Delta-T.
37

Figures A22– A28: 2001 September 21-Thompson Tower Data
38

0

10

20

30

40

50

60

70

80

90

100

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Relative Humidity (%)

RH [2m]

RH [38m]

15

20

25

30

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Temperature (C) 

Temp [2m]

Temp [38m]

Figure A23. Thompson Tower-2001 September 21: Relative Humidity.

Figure A22. Thompson Tower-2001 September 21: Temperature.
39

0

90

180

270

360

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Wind Direction (deg) 

WD [5m]

WD [39m]

0

1

2

3

4

5

6

7

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Wind Speed (m/s)

WS [5m]

WS [39m]

Figure A24. Thompson Tower-2001 September 21: Wind Speed.

Figure A25. Thompson Tower-2001 September 21: Wind Direction.
40

0

100

200

300

400

500

600

700

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Solar Radiation (W/m^2)

878

879

880

881

882

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Pressure (mb)

P [33m]

Figure A27. Thompson Tower-2001 September 21: Solar Radiation.

Figure A26. Thompson Tower-2001 September 21: Pressure.
41

-8

-6

-4

-2

0

2

4

6

8

4 5 6 7 8 9 10 11

Local Time (dec hrs)

Delta-Temperature ( C )

Delta-T [38m-2m]

Zero Line

Figure A28. Thompson Tower-2001 September 21: Delta-T.
42
43

This appendix is part of ARL-TR-2827, Surface Layer Stability Transition Research Minimum Neutral

Event-to-Sunrise Time Interval: 2001 September Case Study, U.S. Army Research Laboratory, White

Sands Missile Range, NM 88002-5501.

A Lagrangian (following the parcel) perspective on the atmospheric conditions during the Nighttime

(Stable) to Daytime (Unstable) transition was quantitatively recorded by the Thompson Site rawinsonde

(RAOB) data. A full Test Day’s worth of data is presented on a single plot. The earliest Sub-case

(Stable) is designated with a red solid box; an orange open circle shows the Neutral Sub-case; the

Unstable Sub-case is a green solid triangle and any additional Unstable data is a blue open diamond.

We have purposefully elected to follow the rainbow’s spectrum to make data viewing easier. As a

reminder, the general times designated for each Sub-case were:

Stable 0500–0700 MDT

Neutral 0700–0900 MDT

Unstable 0900–1100 MDT

The 1554 MDT, 2001 September 18 Pre-Test data were included for completeness. The following are

the four sections of Appendix B:

• Figures B1–B4: 2001 September 18 (Wind Speed and Wind Direction were not available for

September 18)

• Figures B5–B10: 2001 September 19

• Figures B11–B16: 2001 September 20

• Figures B17–B23: 2001 September 21

Appendix B: RAWINSONDE Data
44

Figures B1–B4: 2001 September 18-Rawinsonde Data
45

0

1000

2000

3000

4000

5000

6000

7000

0 10 20 30 40 50 60 70 80 90 100

Relative Humidity (%) 

Height (m-AGL)

RH - 1554 MDT 

0

1000

2000

3000

4000

5000

6000

7000

220 230 240 250 260 270 280 290 300 310

Ambient (K) and Dewpoint Temperatures (K)

Height (m-AGL)

Ambient Temp 1554 MDT

Dewpoint Temp 1554 MDT

Figure B2. Thompson Tower RAOB Launch-2001 September 18: Relative Humidity.

Figure B1. Thompson Tower RAOB Launch-2001 September 18: Temperature.
46

0

1000

2000

3000

4000

5000

6000

7000

-40 -30 -20 -10 0 10 20 30 40

Environmental Lapse Rate (K/km) 

Height (m-AGL)

E L R 1554 MDT

Zero Line

0

1000

2000

3000

4000

5000

6000

7000

100 200 300 400 500 600 700 800 900

Pressure (mb)

Height (m-AGL)

P - 1554 MDT

Figure B3. Thompson Tower RAOB Launch-2001 September 18: Pressure.

Figure B4. Thompson Tower RAOB Launch-2001 September 18: ELR.
47

Figures B5–B10: 2001 September 19-Rawinsonde Data
48

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000

15000

16000

17000

18000

0 10 20 30 40 50 60 70 80 90 100

Relative Humidity (%) 

Height (m-AGL)

RH - 0500 MDT 

RH - 0749 MDT

RH - 0915 MDT

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000

15000

16000

17000

18000

170 180 190 200 210 220 230 240 250 260 270 280 290 300

Ambient (K) and Dewpoint Temperature (K)

Height (m-AGL)

Ambient Temp - 0500 MDT

Dewpoint Temp - 0500 MDT

Ambient Temp - 0749 MDT

Dewpoint Temp - 0749 MDT

Ambient Temp - 0915 MDT

Dewpoint Temp - 0915 MDT

Figure B6. Thompson Tower RAOB Launch-2001 September 19: Relative Humidity.

Figure B5. Thompson Tower RAOB Launch-2001 September 19: Temperature.
49

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Figure B7. Thompson Tower RAOB Launch-2001 September 19: Wind Speed.

Figure B8. Thompson Tower RAOB Launch-2001 September 19: Wind Direction.
50

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Figure B10. Thompson Tower RAOB Launch-2001 September 19: ELR.

Figure B9. Thompson Tower RAOB Launch-2001 September 19: Pressure.
51

Figures B11–B16: 2001 September 20-Rawinsonde Data
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Dewpoint Temp - 0750 MDT

Ambient Temp - 0910 MDT

Dewpoint Temp - 0910 MDT

Figure B12. Thompson Tower RAOB Launch-2001 September 20: Relative Humidity.

Figure B11. Thompson Tower RAOB Launch-2001 September 20: Temperature.
53

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Figure B13. Thompson Tower RAOB Launch-2001 September 20: Wind Speed.

Figure B14. Thompson Tower RAOB Launch-2001 September 20: Wind Direction.
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Figure B16. Thompson Tower RAOB Launch-2001 September 20: ELR.

Figure B15. Thompson Tower RAOB Launch-2001 September 20: Pressure.
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Figures B17–B22: 2001 September 21-Rawinsonde Data
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Figure B18. Thompson Tower RAOB Launch-2001 September 22: Relative Humidity.

Figure B17. Thompson Tower RAOB Launch-2001 September 21: Temperature.
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Figure B19. Thompson Tower RAOB Launch-2001 September 21: Wind Speed.

Figure B20. Thompson Tower RAOB Launch-2001 September 21: Wind Direction.
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Zero Line

Figure B22. Thompson Tower RAOB Launch-2001 September 21: ELR.

Figure B21. Thompson Tower RAOB Launch-2001 September 21: Pressure.
59

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing 

data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate 

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

May 2003 

2. REPORT TYPE 

Final 

3. DATES COVERED (From - To) 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

4. TITLE AND SUBTITLE 

Surface Layer Transition Research, Minimum Neutral Event-to-Sunrise Time 

Interval: 2001 September Case Study 

5c. PROGRAM ELEMENT NUMBER 

5d. PROJECT NUMBER 

5e. TASK NUMBER 

6. AUTHOR(S) 

Gail-Tirrell Vaucher, Manny Bustillos 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Army Research Laboratory 

Information Science & Technology Directorate 

Battlefield Environment Division (ATTN: AMSRL-CI-EI) 

White Sands Missile Range, NM 88002-5501

8. PERFORMING ORGANIZATION 

 REPORT NUMBER 

ARL-TR-2827 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM (S) 

U.S. Army Research Laboratory 

2800 Powder Mill Road 

Adelphi, MD 20783-1145

11. SPONSOR/MONITOR'S REPORT 

 NUMBER(S) 

ARL-TR-2827

12. DISTRIBUTION/AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

Near surface target acquisition and EO propagation significantly improve during the Surface Layer Stability Transition (SLST). 

Thus, this research expands Army Chief of Staff Shinseki’s vision from “to see first” to, “to see better.” The SLST is also the 

starting and ending points for the atmospheric convection growth phase, an important factor in chemical warfare modeling. 

 

In 2001, the Meteorological-sensors Integration Team of the Army Research Laboratory conducted the last of three field 

experiments with the primary purpose of characterizing, modeling and exploiting repeatable patterns in the lower portion of the

atmospheric boundary layer. The repeatable patterns investigated were the morning Stability Transitions (ST) or Neutral Events

(NE). The 2001 September 19–21 test dates were selected based on a forecasted minimal time interval between the local 

Sunrise and an Ideal case NE. Two previous field tests addressed the other minimum (March 2001) and a maximum (June 

2001) Sunrise-to-NE time interval. These Tests are documented separately. 

This Surface Layer Stability Transition research pursued two measurement and analysis methods: Eulerian (Tower Data) and 

quasi-Lagrangian (Rawinsonde data). The Experiment’s results validated the Neutral Event Forecast Model, in that all three 

days showed a ST during the forecasted ST time period. Examples of extended and multiple STs were documented by the data, 

further enhancing the characterization of a desert stable-neutral-unstable morning transition over the Equinox time period. The 

information documented in this report serves as a useful building block in support of the primary goal.

15. SUBJECT TERMS

Stability Transition, Neutral Events, Non-Ideal Conditions, Boundary Layer, Extended and Multiple Neutral Events 

16. SECURITY CLASSIFICATION OF: 

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Gail-Tirrell Vaucher 

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